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1 Understanding Environmental Science and Sustainability

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Learning Outcomes

After reading this chapter, you should be able to

• Define environmental science. • Describe the importance of critical thinking, information literacy, and the scientific method. • Analyze the impact of palm oil plantations on biodiversity and the environment in Borneo. • Define the core concepts of natural capital and sustainability. • Define the core concepts of the environmental footprint and the Anthropocene. • Define the core concepts of uncertainty, scale, risk, and cost–benefit analysis.

Section 1.1 Why Study Environmental Science?

1.1 Why Study Environmental Science?

Whether we realize it or not, almost every aspect of our daily lives is dependent on and con- nected to the natural world around us. We are a part of, and not separate from, that natural world. The food we eat, the air we breathe, and the water we drink all originate from the natu- ral world. Perhaps less obvious, the items we use every day—such as the fuel for our cars, the clothes we wear, and our phones and electronic devices—all have their origins in the natural world. At the same time, our everyday actions and use of these products—be it driving, eat- ing, or throwing out the trash—all have an impact on this natural world on which we depend.

The study of environmental science encompasses all of these relationships. At its most basic, environmental science is the study of how the natural world works, how we are affected by the natural world, and how we in turn impact the natural world around us.

Our fundamental dependence on the natural world makes the study of environmental science relevant to all of us. Environmental issues—including deforestation, ozone depletion, water pollution, and climate change—affect us all. These issues are also in the news now more than ever, and they are often at the center of heated political debates. Acquiring an understanding of the basic science behind these debates is thus an important part of becoming an educated citizen and forming your own opinion of the issues. And while you may not go on to make a career in environmental science, you will likely find that this discipline intersects with your major or field of study in some way.

The goal of this book is to help you understand the basics of environmental science so that you can further explore and research environmental issues that interest and affect you directly. Because environmental issues can be so complex, developing solutions requires a solid understanding of policy and scientific concepts. In this book, we will apply natural sci- ence and social science concepts to the study of environmental issues that are in the news every day. The hope is that you—armed with the knowledge, perspectives, and up-to-date information provided in this book—will begin to form your own, informed opinions on these subjects. Ideally, you will also develop ideas about how you as an individual or society more broadly can take action to address some of the most pressing environmental challenges fac- ing the world today. Ultimately, this book aims to empower you as a student both to grasp the environmental challenges facing the world and to do something about them.

Outline of the Book Much of the rest of this chapter, and most of Chapter 2, focuses on introducing you to concepts and ways of thinking that are essential to the study of environmental science and that will appear repeatedly throughout the rest of the book. You can think of these chapters as laying a foundation for your study of specific environmental issues in subsequent chapters. Just as you would not expect to be able to cook or repair cars without the right tools and basic knowledge of those activities, it would be difficult to study environmental issues without the information provided in these first two chapters.

Section 1.1 Why Study Environmental Science?

With a strong foundation in place, we’ll move to the study of human population and material consumption in Chapter 3. Vir- tually all of the environmental challenges we face are thanks to the growing number of people on the planet and high rates of material consumption among some of those people. In this way, we could say that human population growth and material consump- tion are the fundamental drivers of environ- mental change in the world today.

Chapters 4 through 9 focus on specific envi- ronmental issues and challenges: manage- ment of agricultural and forest resources, freshwater resources, oceanic resources, energy resources, atmosphere and climate,

and waste. These chapters involve a heavy emphasis on negative news and challenges, so Chapter 10 aims to end the book on a more upbeat note. While it’s true that we face enormous and complicated worldwide environmental problems, it’s also true that governments, non- governmental organizations (NGOs), corporations, small companies, schools and universi- ties, and individual citizens are taking steps to address and reverse those challenges. We will examine their stories in hopes of inspiring positive change in our own lives.

Key Definitions in Environmental Science While we may hear or use the words environment, environmentalism, and environmental sci- ence quite often, we might not always appreciate what they mean and how they are used in the study of environmental issues. At its most basic level, the environment is everything that surrounds you. This includes all living things (such as animals, plants, and other people), as well as all nonliving things (such as water, rocks, air, and sunlight). A more scientific definition of the environment would be all physical, chemical, and biological factors and processes that affect an organism.

Based on that definition, it should be clear that we are all a part of the environment rather than apart from it. In fact, one major theme of this book is that, despite all the technological gadgets and scientific advances that attract our attention, we are all fundamentally depen- dent on the environment for our well-being and survival. The task of sustaining our agri- cultural resources, forests, water sources, oceans, atmosphere, and climate is not just about “caring” for this creature or “saving” that endangered animal. It’s also about saving ourselves and ensuring that we and generations to come can breathe clean air, drink clean water, and live under relatively stable and benign climate conditions.

Because the environment by definition is basically everything, environmental science is a complex and interdisciplinary field of study. Environmental science draws together knowl- edge and concepts from many disciplines—ecology, biology, chemistry, geology, atmospheric science, physics, economics, political science, and other fields—to understand both how we are impacting the environment and what can be done to lessen that impact.

danielvfung/iStock/Getty Images Plus The biggest driver of environmental change in today’s world is human population growth and rates of consumption, which have increased exponentially in the past 200 years.

Section 1.2 Thinking Critically About Environmental Science

Note that there is a difference between environmental science and environmentalism. Envi- ronmentalism is a social and political movement committed to protecting the natural world. While many environmental scientists likely consider themselves environmentalists, as scien- tists they adopt a more objective approach to the issues they study. This approach is based in large part on the use of the scientific method, an approach to research based on observation, data collection, hypothesis testing, and experimentation. As a student, you are not required or expected to become an environmentalist, but as an educated citizen, you should learn to recognize the critical role played by the scientific method in forming our understanding of the environment and the environmental challenges we face. Such an understanding of the scien- tific method will help you develop critical-thinking skills and enable you to weigh competing claims and arguments about environmental issues.

1.2 Thinking Critically About Environmental Science

Many environmental scientists see their work as largely nonpolitical and noncontro- versial. They are attempting to understand how a particular piece of the environment or system—a stream, a wetland, a patch of forest—functions and what might happen to that system in the wake of pollution or some other environmental disturbance. However, because the findings of this envi- ronmental research are often used in craft- ing and implementing environmental pol- icy, environmental science and debates over environmental issues can become highly contentious and political.

Take, for example, the topic of global cli- mate change (which will be covered in more detail in Chapter 8). Thousands of environmental scientists are engaged in research that is in some way related to the subject of climate change. Some scientists study how combus- tion of fossil fuels or other human activities add greenhouse gases to the atmosphere, others how these gases change the Earth’s energy balance and climate systems, and still others how changes to the climate are affecting trees, animals, and other living organisms.

The majority of these scientists would probably not see their work as contentious or political. They are instead usually motivated by scientific curiosity and a desire to pursue knowledge. However, because the sum of these thousands of research efforts points with overwhelming confidence to the realities of global climate change, and because addressing climate change will require changes to all sorts of economic and social behaviors, the efforts of these envi- ronmental scientists can become politicized. Because of this politicization, it’s important to understand the concepts of critical thinking, information literacy, and the scientific method. Careful application of these approaches to your own study of the environment will help you

patriziomartorana/iStock/Getty Images Plus Environmental scientists aim to understand how different elements of the environment function and how they change in response to other factors, such as pollution.

Section 1.2 Thinking Critically About Environmental Science

develop informed opinions on many issues and help you avoid falling for arguments that are based on opinion and personal belief rather than grounded in facts and scientific evidence.

Critical Thinking and Information Literacy Critical thinking is the objective analysis and evaluation of an issue to form a judgment. In this case, the key term is objective analysis—in other words, analysis that is not based on personal opinion or belief. For example, one of this book’s authors had a student who, while hiking, saw a number of dead birds on the ground near the base of some wind turbines. The student later expressed a conviction that wind power was bad for the environment and should not be used. While there are legitimate reasons to be concerned about the effect of wind turbines on bird (and bat) mortality, this student should also consider what the envi- ronmental impact of other forms of electricity production are. In the authors’ region of the country (Pennsylvania), much of the electricity is produced by burning coal. A better example of objective analysis would be a comparison of the environmental impacts of coal mining and coal burning (including the impact on birds and bats) to the impact of wind turbines.

As you engage with the material in this book, and as you do your own research and form your own opinions about environmental issues, keep the following principles of critical thinking in mind:

• Evaluate the basis for a particular conclusion. What evidence is being presented to support a claim or an argument, and how was that evidence collected?

• Keep an open mind. Attempt to gather information from a variety of perspectives before forming a final opinion.

• Be skeptical. While keeping an open mind, ask yourself where information is coming from and how it was developed.

• Consider possible biases, including your own. Most scientists strive mightily to avoid the introduction of bias into their work, and the scientific method (described in more detail later) helps them do that.

• Distinguish between facts and values or opinions. For example, it is a fact that atmo- spheric concentrations of the greenhouse gas carbon dioxide now exceed 400 parts per million (ppm) compared to levels of roughly 280 ppm at the start of the Indus- trial Revolution. However, it’s an opinion or value statement to say that the use of all fossil fuels should be halted immediately to prevent further increases in carbon dioxide concentrations.

A key part of establishing and utilizing critical-thinking skills is to develop what’s often referred to as information literacy. Information literacy is the ability to know when informa- tion is needed and the ability to identify, locate, evaluate, and effectively use that information to address an issue. For our purposes, the most important of these abilities will be locating and evaluating information. The past two decades have witnessed an explosion of informa- tion and information sources, and our ability to access that information is becoming easier every day. However, our ability to know where to look for reliable information and to evaluate that information for reliability and usefulness has not kept pace. For example, there are thou- sands of sources of information on the topic of climate change. Who should you believe? Who

Section 1.2 Thinking Critically About Environmental Science

can you trust? We can see how critical-thinking skills are needed for information literacy and how information literacy is required for critical thinking. As you read this book and explore on your own the environmental topics and issues that interest you, ask yourself where infor- mation is coming from, how it was gathered, and how reliable it might be. The Apply Your Knowledge: Is This Information Reliable? feature box presents one quick opportunity to test your critical-thinking skills.

A less appreciated but nevertheless important skill for environmental analysis and problem solving is creative thinking. As scientists examine an environmental issue and ponder its possible causes and consequences, it helps if they can think creatively and with an open mind, as opposed to being locked into one way of looking at the world. Environmental scientists also tap into creative thinking to design effective field experiments that help them better understand the workings of nature. And as we’ll see throughout this book, it will take creative thinking and even imagination to develop alternative approaches to meeting our food, water, energy, and other resource needs in ways that do not destroy the environment.

Apply Your Knowledge: Is This Information Reliable?

Evaluating the quality and reliability of information can be a difficult task, especially when we are considering resources found on the Internet. We live in a world in which opinions are sometimes presented as the unbiased truth, and pretty much anyone with a computer can create a convincing website that is accessible to the entire world.

To highlight some of these challenges, let us explore a website called Save the Pacific Northwest Tree Octopus. At first, the prospect of a tree-dwelling octopus might seem absurd, but nature often surprises us. There are birds that can swim and fish that can fly, so why not an octopus that climbs trees? If you read the article, you might also notice that the information presented is fairly detailed. The author provides a Latin name for this creature, along with measurements that describe tree octopus physiology. There are even photographs and links to additional resources, suggesting that others have documented these creatures in the past.

Despite the website’s flashy appearance, it is a total hoax. There is no such thing as a tree octopus, and if we take a closer look at the website, we can see some warning signs that call its information into question. Take a moment to explore the Save the Pacific Northwest Tree Octopus website on your own, and see if you can find any red flags indicating that the article is unreliable.

(continued)

https://zapatopi.net/treeoctopus/

Section 1.2 Thinking Critically About Environmental Science

Apply Your Knowledge: Is This Information Reliable? (continued)

One characteristic of trustworthy information is that it comes from a reputable author or organization. For example, information from a government agency, an institution of higher education, or a peer-reviewed journal is often considered to be more reliable than information from a personal blog. Reliable resources will also provide access to author biographies so that you can tell if the author is an expert on the subject matter. If you look at the author information at the bottom of the tree octopus website, you will notice that the author description is downright silly. There is no indication that the person has any training related to the subject matter.

Reliable resources also need to be fact-checked or backed up with supporting information that is usually identified using links and citations. This website appears to have active links to other resources, but if you follow these links, you will notice that they take you to other hoax websites or to sites that have no mention of tree octopuses.

Finally, reliable sources will be clear about whether their goal is to inform you with factual information or to convince you of a particular argument. A close reading of the material can often tell you if an unreliable resource is trying to convince you of an opinion while appearing to present objective facts. Consider the following sentence from the tree octopus website:

Tree octopuses became prized by the fashion industry as ornamental decorations for hats, leading greedy trappers to wipe out whole populations to feed the vanity of the fashionable rich. (Zapato, n.d., para. 8)

Phrases like “greedy trappers” and “vanity of the fashionable rich” suggest that the author is making judgments about certain actions and groups of people. This is not what we would expect from a well-written article that is intended to present factual information.

Now, take a moment to explore another web resource titled “Discovery of the First Endemic Tree-Climbing Crab.” Once again, the topic sounds bizarre, but if we look closely, the information seems much more trustworthy. The article was produced by an academic institution. The language used in the article appears to be unbiased, and the information can be easily fact-checked using the peer-reviewed journal articles and academic websites that are referenced at the end. This article appears to be a source of reliable information.

Save the Pacific Northwest Tree Octopus is a silly example of “bad” information, but the critical-thinking skills we used to evaluate this source can be applied to everything that we read, hear, and watch. If we approach media critically, we’ll be able to recognize the trustworthy information that helps us make better policies and decisions. In your future studies, look for information that is from a trusted source. Look for information that is backed up by quality research and journalism. Finally, look for information that is attempting to inform rather than persuade (unless you are researching opinions, of course).

https://www.purdue.edu/fnr/extension/discovery-of-the-first-endemic-tree-climbing-crab/

https://zapatopi.net/treeoctopus/

Section 1.2 Thinking Critically About Environmental Science

The Scientific Method The use of the scientific method is one way that environmental scientists seek to improve the reliability, usefulness, and relevance of their research. The scientific method is an approach whereby scientists observe, test, and draw conclusions about the world around us in a sys- tematic manner, rather than simply stating opinion. The scientific method consists of a series of five steps, as illustrated in Figure 1.1.

Figure 1.1: The scientific method

The scientific method is a five-step model used to observe, test, and draw conclusions scientifically.

1. Make observations

2. Ask questions

3. Formulate hypothesis

4. Make predictions

5. Test predictions

Scenario A: Test supports hypothesis. Additional predictions

can be made and tested.

Scenario B: Test does not support hypothesis. Formulate

new hypothesis and retest.

Section 1.2 Thinking Critically About Environmental Science

Scientists begin with simple observations of the world around us. They then form questions based on those observations. For example, environmental scientists might observe the death and decline of numerous trees alongside a major highway and naturally wonder what is caus- ing this to happen. This leads to the third step, the formulation of a hypothesis or hypotheses that might explain the trees’ death. Hypotheses can be thought of as a first guess or “hunch” about something, and they help scientists formulate predictions, specific statements that can be tested. In this case, the scientists might form a hypothesis that the trees are dying because of road salt running off the highway in the winter or because of an herbicide sprayed to con- trol weeds on the side of the highway. Based on these guesses, they can take the fourth step in the scientific method and develop specific and testable predictions about how much road salt or herbicide needs to be applied to bring about the same levels of tree death and decline they have observed in nature.

All of these steps lead up to the final step of testing the predictions. To clearly determine what might be killing the trees, scientists devise experiments that attempt to hold conditions con- stant and then change one variable at a time. In this case, scientists might identify four similar small groves of trees that show no sign of stress or tree death. They might then expose one area to road salt, another to herbicide, and a third to both road salt and herbicide, while the fourth area is left alone. (Apply Your Knowledge: How Does Road Salt Affect Trees? shows how scientists might record their data.)

Note that regardless of the outcome of these experiments, scientists will typically still do two additional things. First, if the road salt or herbicide appeared to have some impact on the trees, the scientists might refine their predictions to gain a better understanding of why this is happening. This might include adjusting the levels of road salt or herbicide to see if they can better determine at what levels these applications become toxic. If the trees were not affected by the road salt and herbicide, the scientists would be forced to revise their hypotheses or form new ones. Second, scientists typically seek to share their results with others, usually by presenting their research at scientific conferences and publishing articles in professional journals. These presentations and papers are subject to analysis and scrutiny by other scien- tists, a process known as peer review. Scientists also have to explain the methods used in their research so that other scientists can run the same experiments, a process known as replica- tion. These two aspects of scientific research, peer review and replication, help ensure the accuracy and legitimacy of the work.

It’s important to recognize just how the scientific method can shield scientists from claims of bias. Scientists don’t really set out to “prove” anything; instead, they observe, ask questions, hypothesize, predict, test, and usually repeat. Politicians’ demands for scientific “proof” are therefore problematic. Environmental policy should be informed by the best science avail- able, as well as other issues such as ethical concerns, economic impacts, and risks involved.

Section 1.2 Thinking Critically About Environmental Science

Apply Your Knowledge: How Does Road Salt Affect Trees?

Environmental scientists make use of many different types of graphs to summarize and present the data they gather in their research. Graphs help in taking enormous amounts of data and information and presenting them in a way that tells a story or makes an argument. Your ability to understand and interpret graphs will be an important part of reading this book and learning environmental science.

Consider the following figures, which show possible results from the road salt/herbicide example used in the discussion of the scientific method. Figures 1.2 and 1.3 report basically the same information on tree death and decline from the experiment in different ways. Figure 1.2 portrays the number of trees that died in the different plots of the experiment over time. Figure 1.3 presents overall tree deaths by plot type at the end of the experiment.

Figure 1.2: Line graph showing tree damage

This graph shows tree damage over time.

Week 1

Week 2

N u

m b

er o

f tr

ee s

sh o

w in

g s

tr es

s o

r d

am ag

Week 3 Week 4

No application

Road salt

Herbicide

Road salt and herbicide

(continued)

Section 1.2 Thinking Critically About Environmental Science

Based on the data presented from this experiment, it appears that road salt might be the biggest contributor to tree mortality. Imagine then that the scientists conducted a second experiment with four plots of trees in which they applied different amounts of road salt and measured tree mortality over a 4-week period. Table 1.1 gives information on the amount of road salt applied to each of the four plots and the corresponding tree mortality. Try plotting these numbers on a piece of paper. Draw a straight line that comes closest to connecting each of the four points on the graph. What does the shape and direction of this line tell you about the relationship between road salt application and tree mortality?

Table 1.1: Amount of road salt and tree damage

Road salt application (metric tons/hectare) Tree damage (dead trees per plot)

Plot 1 (1 metric ton/hectare) 2

Plot 2 (2 metric tons/hectare) 5

Plot 3 (3 metric tons/hectare) 8

Plot 4 (4 metric tons/hectare) 12

Figure 1.3: Bar graph showing tree damage

This graph shows tree damage by plot type.

No application

0 Road salt

N um

be r o

f t re

es s

ho w

in g

st re

ss o

r d am

ag e

HerbicideRoad salt and herbicide

Apply Your Knowledge: How Does Road Salt Affect Trees? (continued)

Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

1.3 Case Study: Palm Oil Production and Deforestation in Borneo

Environmental scientists, as well as other natural and social scientists, frequently make use of “case studies” to illustrate important points or concepts. In some ways, case studies are simply formalized stories about a specific place, person, group, or other thing. The case study presented here will help illustrate concepts and terms such as environment and environmen- tal science and demonstrate how environmental scientists make use of critical-thinking skills and the scientific method in their work. This case study will also be used to explain some of the foundational concepts introduced later in this chapter and in Chapter 2.

About Borneo The island of Borneo straddles the equator in Southeast Asia and is the third largest island in the world and the largest island in Asia. The island is divided between Indonesia, Malaysia, and Brunei, with Indonesia controlling roughly 73% of Borneo’s land area, Malaysia 26%, and tiny Brunei just 1% (see Figure 1.4).

Figure 1.4: Borneo

Located in Southeast Asia, Borneo is known for its high rates of biodiversity, but its rain forests are in decline due to deforestation

Adapted from PeterHermesFurian/iStock/Getty Images Plus

BORNEO

Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

Until very recently, Borneo was sparsely populated, and much of the island was covered in dense tropical rain forests. Because of this, Borneo is known for its extremely high rates of biological diversity, or biodiversity—the variety of life and organisms in a specific ecosys- tem. That variety can be measured by considering the number of species found in a particu- lar area. Species are groups of organisms that share certain characteristics, interbreed, and produce fertile offspring. In addition to having an incredibly high number of species overall, Borneo is also known for having a large number of endemic species—plants and animals that exist in only one specific geographic region. There are dozens of endemic mammal spe- cies (such as the proboscis monkey and pygmy elephant), hundreds of endemic birds, and thousands of endemic plant species in Borneo. Rates of biodiversity are so high in Borneo that scientists have identified over 20,000 types of insect species in one small national park alone (Shoumatoff, 2017).

The Problem Beginning roughly 50 years ago, Borneo’s rain forests began to decline in dramatic fashion. Actions such as logging trees for timber, clearing land for small-scale agriculture, and burn- ing large tracts of forest to clear land for palm oil plantations have reduced the island’s forest cover from 75% in the mid-1980s to less than 50% today. Current rates of deforestation— clearing of forest areas—in Borneo are estimated to be 1.3 million hectares (over 3 million acres) a year (World Wide Fund for Nature, 2019).

Among the major drivers of deforestation in Borneo, conversion of rain forests to palm oil plantations is currently the most significant. Palm oil is derived from the nuts of the oil palm tree and is now the second most important oil used in consumer products after petroleum. Palm oil is a $50-billion-a-year industry (Shoumatoff, 2017), and it is used in a vast array of household and consumer products, including cooking oil, snack foods, chocolate, cosmet- ics (such as lipstick), toothpaste, ramen noodles, shampoo, ice cream, cookies, and soap. It’s estimated that palm oil is an ingredient in roughly half of all packaged products sold in mod- ern supermarkets. Millions and millions of acres of rain forest have been cut and burned in Borneo to make way for palm oil plantations, and this deforestation continues today. Because most of us probably consume products made with palm oil, we are all in some way connected to this problem.

pxhidalgo/iStock/Getty Images Plus Much of Borneo’s tropical rain forest has been razed for palm oil plantations.

Laszlo Mates/iStock/Getty Images Plus

Section 1.3 Case Study: Palm Oil Production and Deforestation in Borneo

The Impact Conversion of Borneo’s rain forests to palm oil plantations may result in a number of serious environmental and social problems. Many different types of wildlife depend on forests as their natural habitat—the place or set of conditions an organism depends on for survival— so deforestation leads to high rates of biodiversity loss and extinction, or the total loss of a species. Cutting up rain forests also results in habitat loss, driving wildlife species into smaller and smaller areas for survival. Loss of tree cover leads to increased flooding as heavy tropical rains run off cleared hillsides instead of being absorbed by dense forest soils and vegetation. This flooding also results in water shortages later on, since rainwater rushes to rivers and the sea instead of replenishing local groundwater supplies. Lastly, burning of for- ests worsens climate change in two ways. First, the combustion of trees and other vegetation pours millions of tons of carbon dioxide, a greenhouse gas, into the atmosphere. We’ll see in Chapter 8 that increased greenhouse gas concentrations are resulting in global warming and climate change. Second, the ability of those forests to absorb and store vast amounts of car- bon from the atmosphere is lost.

Borneo’s extremely high rates of biodiversity, combined with the widespread deforestation of the past few decades, make this island one of the world’s most important biodiversity hotspots. A biodiversity hotspot is a region that both has high rates of biodiversity and is experiencing significant environmental destruction. There are roughly 25 regions of the world that scien- tists have labeled as biodiversity hotspots. Scientists hope that by calling attention to these regions and the endangered species—species at risk of extinction—that live there, they can encourage governments, businesses, and private citizens to take action to address the prob- lem before it is too late.

A Scientific Approach Let’s consider how environmental scientists approach the study of an issue like palm oil pro- duction and deforestation in Borneo. First, it’s clear that our own understanding of what’s happening in Borneo is the result of interdisciplinary research by many different kinds of scientists and experts. Botanists, entomologists, and ornithologists research Borneo’s plants, insects, and bird species, respectively. Wildlife biologists examine how deforestation is driv- ing endangered species into smaller geographic areas. Hydrologists seek to understand the impacts of deforestation on flooding and water supplies. Atmospheric scientists and soil sci- entists attempt to understand how deforestation impacts carbon storage and greenhouse gas emissions from forest soils. Remote sensing specialists use satellite imagery to measure rates of deforestation over time. Environmental health specialists study the impact of pesticide and herbicide spraying of palm oil plantations on local human populations. And social scien- tists—economists, anthropologists, policy experts—study what’s driving deforestation, how local human populations are responding, and what might be done in terms of policies and economic incentives to address this challenge.

All of these scientists and experts apply critical-thinking and information-literacy skills to their work. Most of them also make regular use of the scientific method in defining and carry- ing out research in their specific areas. For example, a botanist (plant expert) or ornithologist

Section 1.4 Core Theme: Sustaining Our Natural Resources

(bird expert) might conduct research to measure the number and variety of plant and bird species in intact forest areas as well as in forest areas that have been fragmented or disturbed. Hydrologists (water experts) might study rates of water flow and water quality in different river basins that are characterized by different levels of deforestation. These and other sci- entists working in a setting such as Borneo might care deeply about wildlife and feel terrible about the environmental destruction they see, but they still approach their work in an objec- tive and scientific manner.

1.4 Core Theme: Sustaining Our Natural Resources

The remainder of this chapter will focus on introducing you to a series of concepts and terms that will be important as we explore specific environmental issues in subsequent chapters. This foundation of knowledge will provide you with a vocabulary and way of thinking that will help frame the rest of the book. As we discuss these concepts and terms, we will return to the example of deforestation in Borneo to better understand their meaning. We’ll start with the concepts of natural capital and sustainable development. These concepts lie at the core of environmental scientists’ work, which often focuses on supporting the environment that we all depend on and are all a part of.

Natural Capital and Ecosystem Services Most of us have experienced a power outage, an Internet outage, a road closure, or disrup- tion in some service that we depend on in our day-to-day lives. Such disruptions often remind us of the basic infrastructure (such as the power supply, the water supply, and functioning roads) we depend on but usually take for granted. In much the same way, and to an even greater degree, we depend on the natural world, the environment, and the natu- ral systems that make up the environment for our well-being and survival. Yet we seldom if ever really think about that dependence and what it means to our quality of life.

Environmental scientists refer to this natural infrastructure as natural capital. Natural capital can be defined as natural assets such as trees, soils, streams, oceans, and the atmosphere. Like other forms of infrastructure, because natural capital is all around us, we seldom give it much thought. Take, for example, the tropi- cal rain forests of Borneo. Managed properly, these forests could yield a steady supply of tim- ber, fruit, and other nontimber forest products such as rubber, medicinal plants, and building materials like bamboo. These forests could also be a destination for ecotourism, tourism that

staticnak1983/E+/Getty Images Ecosystems, derived from the Greek word for home, provide us with areas for recreation, spirituality, and joy.

Section 1.4 Core Theme: Sustaining Our Natural Resources

focuses on natural environments in an effort to help conserve an area and support the local economy.

But understanding natural capital requires us to think more broadly than just in terms of resources. Even as valuable as all of these things—timber, nontimber products, and tour- ism—might be, they only scratch the surface of the real value humans derive from such eco- systems. These stocks of natural capital, through their normal functioning, generate a flow of life-sustaining ecosystem services that are absolutely essential for human survival (see Figure 1.5). We’ll learn more about what ecosystems are in Chapter 2, but for now think of them as complex systems made up of both living organisms and nonliving components. For example, forests help purify air and water supplies, help prevent extremes of drought and floods, provide space and conditions for the decomposition of wastes, provide habitat for pol- linating insects and birds that are essential to agriculture, and play a critical role in storing carbon and maintaining regional and global climate systems. Even this list is incomplete, and this is only describing the services of one ecosystem. Other systems—grasslands, wetlands, coral reefs, tundra, deserts, coastal systems, and open oceans—all provide their own ecosys- tem services that are essential to our survival.

Figure 1.5: Natural capital and ecosystem services

Stocks of natural capital are all around us and generate a flow of ecosystem services and value for humans.

Adapted from “What Is Natural Capital?” by Natural Capital Coalition, n.d. (https://naturalcapitalcoalition.org/natural-capital-2).

Natural capital stocks Ecosystem services

CO2 O2

Yield

A simple analogy would be to think of a home. Earth’s natural systems, like a home, take care of climate control, air purification, the provisioning of food and water, and waste disposal and puri- fication. They provide us spaces for recreation, spiritual growth, and moments of joy. It’s perhaps no accident that the prefix eco– in ecosystem is derived from the Greek word oikos, or “home.”

In the chapters ahead, try to apply this analogy and the concepts of natural capital and eco- system services to issues of soil depletion, deforestation, water and air pollution, overfishing, climate change, ozone depletion, and toxic waste dumping. What are we doing to our home

https://naturalcapitalcoalition.org/natural-capital-2

Section 1.4 Core Theme: Sustaining Our Natural Resources

when we create these problems? How might our actions be destroying natural capital and undermining the very systems we all depend on? What would alternative approaches, those focused on sustaining natural capital, look like?

Sustainability and Sustainable Development The concepts of sustainability and sustainable development come up a lot in discussions of the environment. But what do they really mean? At a basic level, and applied to issues of the envi- ronment, sustainability is the maintenance of natural systems and an ecological balance. Sustainable development brings human and economic needs into the picture and is the achievement of economic objectives without the depletion or destruction of natural systems. In other words, sustainability and sustainable development suggest a balancing act between meeting the needs of humans and maintaining the integrity of our natural environment.

Understanding the concepts of natural capital and ecosystem services means understanding that sustainable development is the only way forward for the human species. Development that is not sustainable, that destroys or depletes natural systems and natural capital, will only undermine the basic ecological systems that we all depend on. In this sense, it should be clear that viewing economic progress and environmental protection as competing goals is ulti- mately foolish and misguided. We cannot sustain economic progress and human well-being if, at the same time, we are undermining and destroying the natural infrastructure that makes such progress possible.

Unfortunately, much economic activity and economic development we see around the world today is unsustainable. Think of a business or a household trying to make ends meet. That business or household might be able to balance its books month to month by selling off equip- ment or other assets, but eventually this approach is not sustainable. Likewise, much of the economic progress in recent decades has been based on liquidating, or using up, natural capi- tal such as oil, coal, soils, forests, fisheries, mineral stocks, and other resources. This economic progress has also generated massive amounts of pollution and waste products, and this pol- lution is overwhelming the natural ability of many ecosystems to provide air and water puri- fication services. In other words, our current economic progress and economic systems do not meet the definition of sustainability and instead result in natural capital depletion and destruction.

In Borneo, logging for timber, clearing forests for agriculture, and widespread burning of forests to make way for palm oil plantations represent one approach to economic develop- ment—but in most cases one that is not sustainable. Overexploitation of timber resources and logging faster than the rate of tree regrowth ultimately reduce the productivity of that forest and make it less valuable over time. They also increase the risk of flooding, reduce water supply, and diminish water quality, all outcomes that actually reduce quality of life and impose costs on society. Likewise, conversion of tropical forests in Borneo to palm oil planta- tions may result in a short-term boost to the local economy and provide some employment opportunities. However, plantation establishment also results in flooding, water contami- nation, loss of forest products, and other problems that might very well offset any positive economic gains.

Section 1.5 Core Theme: Examining Our Impact

In this way we can see how the concepts of natural capital and sustainability are tightly linked. Sustainable economic development does not depend on the destruction and liquidation of natural systems and natural capital, and therefore it does not undermine people’s future ability to enjoy the services and benefits of these systems. Instead, sustainability means that we strive to meet our needs in ways that maintain stocks of natural capital and the ecologi- cal integrity of natural systems. Think about this in the chapters ahead as we examine the environmental and ecological impacts of current approaches to food production, energy use, waste management, and other activities. Also try to imagine what a sustainable approach to these activities might look like.

1.5 Core Theme: Examining Our Impact

Now that we know what we are trying to sustain—natural capital—how do we know if we are actually doing so? What are some indicators that can be used to determine if our economic activities have gone too far and are actually undermining our long-term prospects? This sec- tion will introduce two concepts, the environmental footprint and the Anthropocene, that suggest we are overexploiting natural capital on a worldwide basis and undermining long- term prospects for sustainability.

The Environmental Footprint Few of us give much thought to the impact we have on the environment. If we do think about our impact, we tend to do so mainly in terms of our immediate surroundings. In reality, our lifestyle and consumption patterns often have far-reaching effects on many parts of the envi- ronment in ways that are difficult for us even to imagine. For example, how often do you think about where your water or food comes from? Many of us rely on municipal water systems that might involve pumping water hundreds of miles and running it through a series of filtration and purification systems before distributing it to thousands of households and businesses. Almost all of us depend on commercial food systems that distribute food from all over the world using trucks, boats, trains, and even planes. When you flip a light switch or flush a toi- let, do you think about where that electricity comes from or where that waste is going? All of these services are complex systems that require significant energy and resources, and these systems often have wide-ranging environmental impacts.

Because so many of our activities and consumption patterns have environmental and ecologi- cal impacts that are invisible to us—out of sight, out of mind—environmental scientists have developed the concept of an environmental or ecological footprint. An environmental foot- print is a measure of how much land area and water is necessary to support an individual or a group of people (see Figure 1.6). For example, how much land and water is needed to grow the food you eat or the timber, paper, and forest products you use? How big of an area is needed to effectively absorb and convert the liquid, solid, and gaseous wastes that you produce every day? Because we consume resources in different ways and live different lifestyles, individuals can have different environmental footprints. In terms of diet, for example, it takes more land and water to produce meat than an equivalent amount of grain or vegetables. Therefore, a person with a heavily meat-based diet is likely to have a larger environmental footprint than someone who eats less meat or is vegetarian.

Section 1.5 Core Theme: Examining Our Impact

Figure 1.6: Environmental footprint

If we were to illustrate the United States’ environmental footprint, it might look like this. How much land and water does your lifestyle require?

Adapted from “WWF Report: Global Wildlife Populations Could Drop by Almost 70% by 2020,” by WWF, 2016 (https://www.wwf.org.hk /en/news/press_release/?uNewsID=16820).

Carbon footprint (energy use)

Fisheries

Pasture/livestock

Forest products

Cropland

Built-up land

https://www.wwf.org.hk/en/news/press_release/?uNewsID=16820

Section 1.5 Core Theme: Examining Our Impact

Individual environmental footprints can be summed to determine the overall footprint of a larger group of people, such as a city or an entire country. These cumulative environmental footprints can be measured against the actual amount of land and water resources available to that population in order to determine whether current consumption patterns are sustain- able. In other words, the environmental footprint of a given population is a measure of its natural capital use, and by comparing natural capital utilization to natural capital availability, a determination can be made as to whether that population is behaving in a way that meets the definition of sustainability.

Perhaps not surprisingly, the average environmental footprint of a citizen of a country like the United States, Canada, or France is 5, 10, or even 20 times larger than the environmental footprint of a citizen of a less developed country like Indonesia, Ethiopia, or Bangladesh. Fur- thermore, the overall environmental footprint of developed countries like the United States exceeds the amount of land and water resources available to support their populations on a sustainable basis. In other words, the United States is meeting its current consumption pat- terns only by drawing down or depleting its own natural capital resources or by “borrowing” those resources from other countries. You could say that our environmental footprint shows that we are running a serious ecological deficit. On a global scale, it’s estimated that the entire human population is consuming resources and generating waste products at a rate that would require 1.7 planet Earths to be sustainable (Global Footprint Network, 2019). Obviously, we do not have any other planet Earths available, so we must find ways to reduce the environ- mental impacts of our activities and consumption if we are to reach a sustainable state.

In terms of our Borneo case study, it’s likely that most residents of that island have relatively small environmental footprints, based on their direct consumption patterns. However, global demand from countries like the United States for low-cost palm oil is driving the process of deforestation for palm oil plantations. This example demonstrates how consumption pat- terns in one place can have serious environmental impacts in faraway places. As we examine the impact of food production, water management, fishing, energy use, and waste production on the environment in the chapters ahead, try to connect these to your own consumption and resource use patterns. What do you think your own environmental footprint looks like? What steps could you take to reduce it?

Learn More: Your Environmental Footprint

The Global Footprint Network is the go-to source for information on the idea of environmental or ecological footprints.

• https://www.footprintnetwork.org/our-work/ecological-footprint

https://www.footprintnetwork.org/our-work/ecological-footprint

Section 1.5 Core Theme: Examining Our Impact

The Anthropocene and the Sixth Great Extinction Geologists and earth scientists use a geologic timescale to measure the history of the Earth. One unit of measure in that timescale is an epoch, a particular period of time defined by dis- tinctive features or events. For roughly the past 10,000 years, a geologic epoch known as the Holocene, the Earth has been a fairly stable place. There have been no major shifts in cli- mate, no global extinction events, and no periods of widespread volcanic activity or changes in ocean chemistry.

These relatively stable conditions have provided the perfect setting for human civilizations to grow and flourish. In that time, the human population of the entire planet has grown from roughly a few million people, equivalent perhaps to the current population of Los Angeles, to roughly 7.7 billion people (see Figure 1.7). In just the past 200 years, the human population has increased by a factor of 8, and the rates of consumption, material and energy use, and waste generation per person have also increased dramatically.

Figure 1.7: Human population growth

Scientists wonder if Earth can continue to support the current trajectory of human population growth.

Based on data from “Historical Estimates of World Population,” by U.S. Census Bureau, 2018 (https://www.census.gov/data/tables /time-series/demo/international-programs/historical-est-worldpop.html); “World Population Prospects 2019,” by United Nations DESA Population Division, 2019 (https://population.un.org/wpp).

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https://www.census.gov/data/tables/time-series/demo/international-programs/historical-est-worldpop.html

https://population.un.org/wpp

Section 1.5 Core Theme: Examining Our Impact

As a result of these dual trends—growing numbers of people and increasing rates of material and energy use—some scientists now feel that we are entering a new epoch, one they are calling the Anthropocene. The Anthropocene, derived from the prefix anthropo–, or “human,” can be defined as a geologic age or epoch during which human activities are the dominant influence on the environment, oceans, climate, and other Earth systems. Humans are literally leaving their mark on the planet, including funda- mentally altering the chemical composition of the atmosphere, oceans, and soils; con- verting vast areas of open space to cities, suburbs, farms, and other forms of devel- opment; and driving species to extinction at rates that are 100 to 1,000 times greater than would otherwise be the case.

These rapid increases in extinction rates are leading environmental scientists to worry that we are in the early stages of a sixth great extinction. Scientists believe that since life began on Earth, there have been five great extinction events—periods in which a significant per- centage (70%–95%) of species were wiped out. The first, known as the Ordovician–Silurian extinction event, occurred roughly 440 million years ago. The most recent, known as the Cretaceous–Tertiary extinction event, occurred 65 million years ago. It takes millions of years to bounce back from extinction events and reach comparable levels of species diversity. But under relatively stable conditions, evolutionary processes create new species faster than oth- ers go extinct, and so species diversity will increase over time. Since the last great extinc- tion, the number of species on Earth has grown into the tens of millions. Of these, we know the most about numbers of mammals and birds but far less about the status of fish, rep- tiles, amphibians, plants, and invertebrates (organisms without a backbone, such as insects). Today, as extinction rates increase and far surpass the rate at which evolution develops new species, we could be losing hundreds if not thousands of species before we have had a chance to fully understand and study their place in an ecosystem.

Unlike the first five great extinction events, which were caused by natural forces like mass volcanic eruptions and meteor strikes, the current crisis is a direct result of human actions. Some of these human actions include pollution, overharvesting and overhunting of species, the introduction of exotic or invasive species into ecosystems, and the effects of human- caused climate change. (These and other causes of biodiversity loss and extinction will be reviewed in greater detail in Chapter 2.) However, the most significant cause of species extinction today is habitat destruction, such as that in Borneo. Widespread conversion of tropical forests to palm oil plantations, soybean farms, and grazing areas for cattle is wip- ing out habitat for all kinds of species and contributing significantly to the rapid increase in extinction rates on the island.

naumoid/iStock/Getty Images Plus Human activities are changing the planet. Our choices are affecting the atmosphere, land, oceans, and other species.

Section 1.6 Core Theme: Taking Action

In the chapters ahead, consider how human activities like agriculture, fishing, logging, min- ing, energy use, and waste generation might be altering the planet in profound ways. Also consider what these activities might mean for other species and for rates of biodiversity loss. In doing so, consider an idea proposed by the well-known and highly respected evolutionary biologist E. O. Wilson. Wilson calls for a plan that would set aside one half of the planet as per- manently protected areas for other species, an idea known as the Half-Earth Project. Wilson and others are convinced that such a bold plan is the only way to avert a sixth mass extinction event. Is such an idea even possible? Can we find ways to meet the needs of a human popula- tion soon to exceed 8 billion while leaving room for other species?

Learn More: The Half-Earth Project

The Half-Earth Project is an effort designed to conserve half of the world so as to protect biodiversity and the ecosystem services it provides. You can learn more about this project here.

• https://eowilsonfoundation.org/half-earth-project • https://www.half-earthproject.org

1.6 Core Theme: Taking Action

Faced with evidence that our global ecological footprint is already exceeding capacity and that we are moving rapidly toward what could be a sixth mass extinction, how do we change our approach to economic development and meeting our food, water, and energy needs with- out making things worse? The chapters ahead will present alternative approaches to meeting our needs side by side with a discussion of current approaches. But how do we know if those alternatives are worth pursuing, and how much time do we have to decide whether to pursue them? This section introduces the concepts of uncertainty, scale, risk, and cost–benefit analy- sis that help environmental scientists and policy makers grapple with these questions.

Uncertainty and Scale The concepts of uncertainty and scale play an important role in how we define and address dif- ferent environmental challenges. Uncertainty is a defining characteristic of much of the work done by environmental scientists. The natural systems that these scientists study are often so complex that there are always things they can’t be certain about. The scientific method is one important way in which scientists reduce uncertainty. However, some uncertainty and even ignorance will still be present, and it’s important to understand this when we examine evidence of environmental problems and the need to address them. Waiting for “scientific certainty” before addressing an environmental challenge, a call often made by politicians in

https://eowilsonfoundation.org/half-earth-project

https://www.half-earthproject.org

Section 1.6 Core Theme: Taking Action

cases like climate change, is simply an argu- ment for doing nothing. Instead of waiting on a certainty that will almost never be achievable, policies and other approaches for addressing environmental problems should be based on the best possible sci- ence available at that moment, even if it still includes elements of uncertainty.

The concept of scale is also important to con- sider as you undertake the study of environ- mental science. Environmental issues occur at many different scales—local, regional, national, and global—and the larger the scale, the more complex and difficult it tends to become to deal with these issues. For example, small-scale deforestation in

Borneo may be mainly a local scale issue that might be understood and addressed in a fairly direct fashion. If the scale of that deforestation increases, either because of larger clearings or a larger number of small clearings that have begun to connect, then we might move to a regional scale issue with broader impacts. Understanding those impacts and developing ways to address them also grow in complexity.

At this point, deforestation in Borneo has actually reached the level of a national and global scale issue. National governments and international environmental groups are involved in defining and attempting to reduce the problem. Global demand for palm oil and other prod- ucts is driving deforestation not only in Borneo but also in the Brazilian Amazon and regions of central Africa. Meanwhile, land use practices in Borneo are resulting in biodiversity loss, air pollution, and greenhouse gas emissions that are felt on a global scale.

As we study a variety of environmental issues in the chapters ahead, consider how issues of uncertainty and scale might affect debates about the scope of the problem and possible solutions. Understand that scientists readily acknowledge elements of uncertainty in their work and in what they study, but this does not mean they don’t know what they are talking about, nor is it an excuse for inaction. Also consider how environmental issues operate at different scales and whether you can see this in your own actions and their impacts on the environment.

Risk and Cost–Benefit Analysis We make decisions about risk in our lives every day. Every time you fly on an airplane, drive a car, walk to work, fall in love, decide to have a family, or enter a business relationship, you incur a risk that something will go wrong. Therefore, whether you are conscious and deliber- ate in your choices or reckless and haphazard, you are making a personal form of risk analy- sis, or risk assessment.

zanskar/iStock/Getty Images Plus Action needs to happen early. If we wait for scientific certainty before addressing issues, then we might face irreparable damage to our environment and its creatures.

Section 1.6 Core Theme: Taking Action

In a similar manner, society must make risk analyses in setting environmental policy. You can see this type of decision making in the news almost every day, along with the political and economic arguments on a local, state, or national level. For any issue, there are a series of simple questions that must be addressed before choosing a path of action.

First, one must ask, “What is the probability that a given activity will cause harm?” Because systems are so complex, it is seldom possible to say action A definitely will cause consequence B. Scientists build models based on experiments and observation and test their models to the best of their ability. Rational nonscientists must then develop a course of action based on the probabilities expressed by the majority of scientists working in the field.

Second, given that outcomes are usually uncertain, one must ask, “What are the consequences if we do nothing?” In our normal lives, we spread a bigger safety net when the consequences are serious than we do when they are minor. If the brakes were likely to fail on your car, you would act more aggressively to get them fixed than you would if the interior dome light were not working. Because outcomes are never certain, we must balance risk and consequence in setting environmental policy.

Finally, one must ask, “What are the costs and risks of choosing other options?” In the case of Borneo, we know with a lot of certainty that current land use practices are not sustain- able. We also know that things will only get worse if we do nothing. The real question comes when we consider what other options might exist. Environmental scientists, economists, and other development experts can point to many alternative land use practices and economic models that could help better protect Borneo’s environment while still providing livelihood opportunities to its residents. However, these alternative approaches may do less to enrich certain members of society who hold a disproportionate amount of political power. Alterna- tive approaches might make sense from an overall societal perspective, but they might not be implemented due to local, regional, national, and even global political realities.

One commonly used tool in environmental risk assessment is cost–benefit analysis. It costs money to install pollution control in factories, mining operations, automobiles, power plants, and other human-operated systems. These pollution control costs are called internal costs because they are borne by the industries that produce specific goods and services. Consum- ers pay internal costs whenever they turn on electricity, pump gasoline into a car, or buy anything at the store. But if pollution control is nonexistent or inadequate, then everyone has to pay the cost of a dirty and unhealthy environment. Environmental disasters can result in sickness, death, destroyed property, loss of work, reduction of home values, and so on. These societal costs of unregulated pollution are called external costs, or externalities, because they are outside the activity itself and are not reflected in direct costs. External costs are paid by everyone in society, regardless of what he or she purchases. Thus, if electric generation cre- ates pollution that causes negative health effects, a poor person who uses little electricity pays the same price as a rich person who uses a lot of electricity. In fact, a poor person is likely to pay an even higher price, since many electric power plants and other polluting industrial facilities (such as oil refineries) tend to be located in low-income areas.

Cost–benefit analyses can be used to compare the cost of pollution control with the cost of externalities. For example, as the cost of pollution control increases, the cost of externali- ties decreases. The total cost to society can be found by combining costs of pollution control and externalities. This total cost typically reaches a minimum when some, but not all, of the

Bringing It All Together

pollution is controlled. Many suggest that we should strive to achieve this minimum cost even though this approach accepts some pollution, with its possible discomfort, sickness, and even death. They argue that the alternative, more expensive pollution control, will slow economic growth and lead to unemployment, with its own forms of human misery. Others argue that that cost–benefit analysis is flawed because it ignores both the quality and the value of human life. How, they ask, can you place a dollar value on the spiritual quality of a walk in the woods or a swim in a crystal clear mountain stream? How can you measure the economic value of even one life cut short by cancer? If noneconomic costs of pollution are considered, then more pollution control becomes desirable.

No one knows the future. But the outcome will affect every person on the planet. We study environmental science because the issues facing society are complex. There are no absolute answers. But certainly we—as individuals, municipalities, states, countries, and citizens of the world—need to develop scientific, economic, and political policy based on an accurate evalu- ation of the problems we face today and the future we envision for tomorrow. Certainly, an informed awareness is essential to making the decisions that will affect all of us. As we study specific environmental issues in the chapters ahead, think about how issues of uncertainty, scale, and risk might combine to shape perceptions and attitudes about how best to address that environmental challenge. Also consider whether making use of risk analysis and cost– benefit analysis might help in guiding policy makers to a better resolution of that challenge.

Bringing It All Together

This opening chapter introduced you to a lot of new terminology, concepts, and ways of seeing the world. The goal is not to just have you memorize what these terms and concepts mean but to provide you with the tools you need to further explore a range of environmental issues presented in the chapters to come. This chapter also provided you with the oppor- tunity to begin to think about your own connection to the environment, in terms of both your dependence and your impact on it. The next chapter will continue to introduce you to concepts and terms important to the study of environmental science. The focus of Chapter 2, however, will be on the field of ecology and establishing a natural science foundation. As we move to Chapter 3 and its focus on human population growth and material consumption, and then to Chapters 4–9 with their focus on specific environmental issues and challenges, see if you can connect and apply the terms and concepts introduced in this chapter to your own understanding of the material.

Additional Resources

Our Connection to the Natural World

We seldom think about the important question of whether we view ourselves as apart from nature or as a part of nature. In this interesting essay, leadership consultant Kathleen Allen asks that question and what the answer might mean for each person’s leadership style.

• https://kathleenallen.net/are-we-a-part-of-nature-or-are-we-apart-from-nature

https://kathleenallen.net/are-we-a-part-of-nature-or-are-we-apart-from-nature

Bringing It All Together

This TED Talk argues that nature is not just some pristine wilderness thousands of miles away from where we live, but rather any open space right outside our door. By going out into that space, we can develop a relationship with nature that’s good for us and for the planet.

• https://www.youtube.com/watch?v=hiIcwt88o94

Critical Thinking

Educator and speaker Michael Stevens has developed something of a cult following around his TED Talks on YouTube videos that deal with how we ask and answer questions. His insights shine a light on how scientists approach their work and use a combination of cre- ative and critical thinking to ask and answer questions about the world around them.

• https://www.youtube.com/channel/UC6nSFpj9HTCZ5t-N3Rm3-HA

Deforestation in Borneo

There has been a lot of good coverage of the deforestation issue in Borneo in recent years, including analysis of its causes, history, future trends, and how our own consumption deci- sions might be implicated in that destruction. This well-written and insightful piece exam- ines the issue and what part you might play in reversing it.

• https://news.mongabay.com/2018/02/borneo-ravaged-by-deforestation-loses -nearly-150000-orangutans-in-16-years-study-finds

Natural Capital and Ecosystem Services

Natural capital and ecosystem services can sometimes be difficult concepts to understand. These resources help explain what natural capital and ecosystem services are and why they are so important for human well-being and survival.

• https://naturalcapitalcoalition.org/natural-capital-2 • https://wle.cgiar.org/content/what-are-ecosystem-services

Sustainability and Sustainable Development

The United Nations is attempting to make the concepts of sustainability and sustainable development a reality through its Sustainable Development Goals. You can learn more about these efforts and the idea of sustainability in general at these sites.

• https://sustainabledevelopment.un.org/?menu=1300 • https://www.undp.org/content/undp/en/home/sustainable-development.html

The Anthropocene and the Sixth Great Extinction

The idea of the Anthropocene and the question of whether we are now entering this new epoch are being hotly debated among environmental scientists and geologists. Learn more about this concept, and the scientific debate surrounding it, here.

• http://www.anthropocene.info • https://theanthropocene.org

https://www.youtube.com/watch?v=hiIcwt88o94

https://www.youtube.com/channel/UC6nSFpj9HTCZ5t-N3Rm3-HA

https://news.mongabay.com/2018/02/borneo-ravaged-by-deforestation-loses-nearly-150000-orangutans-in-16-years-study-finds

https://naturalcapitalcoalition.org/natural-capital-2

https://wle.cgiar.org/content/what-are-ecosystem-services

https://sustainabledevelopment.un.org/?menu=1300

https://www.undp.org/content/undp/en/home/sustainable-development.html

http://www.anthropocene.info

https://theanthropocene.org

Bringing It All Together

Key Terms Anthropocene A geologic age or epoch during which human activities are the domi- nant influence on the environment, oceans, climate, and other Earth systems.

biodiversity The variety of life and organ- isms in a specific ecosystem.

biodiversity hotspot A region that has high rates of biodiversity and is also experiencing significant environmental destruction.

cost–benefit analysis A systematic approach to calculating and comparing the costs and benefits of different policies.

creative thinking The ability to analyze and address situations and challenges in new and creative ways.

critical thinking The objective analysis and evaluation of an issue in order to form a judgment.

deforestation The act of clearing of forest areas.

ecosystem services The beneficial resources and processes that ecosystems supply to humans.

ecotourism Tourism that is focused on natural environments in an effort to help conserve an area and support the local economy.

endangered species Species at risk of extinction.

endemic species Plants and animals that exist in only one specific geographic region.

environment Everything that surrounds us, including living and nonliving things; all physical, chemical, and biological factors and processes that affect an organism.

environmental footprint A measure of how much land area and water is neces- sary to support an individual or a group of people.

environmentalism A social and politi- cal movement committed to protecting the natural world.

environmental science The study of how the natural world works, how we are affected by the natural world, and how we in turn impact the natural world around us.

extinction The total loss of a species.

habitat The place or set of conditions an organism depends on for survival.

habitat loss The destruction of specific habitats.

Holocene The current epoch or geologic time period, roughly the past 10,000 years.

information literacy The ability to know when information is needed and the ability to identify, locate, evaluate, and effectively use that information to address an issue.

interdisciplinary Pertaining to multiple disciplines, or areas of study.

natural capital Natural assets such as trees, soils, streams, oceans, and the atmosphere.

Bringing It All Together

risk analysis An evaluation that considers the probability that a given action will cause harm, the consequences of inaction, and the costs and risks of other options. Also known as risk assessment.

scientific method An approach to research based on observation, data collection, hypothesis testing, and experimentation.

species Groups of organisms that share cer- tain characteristics, interbreed, and produce fertile offspring.

sustainability The maintenance of natural systems and an ecological balance.

sustainable development The achieve- ment of economic development without the depletion or destruction of natural systems.

2 Understanding Ecology and Biodiversity

RICARDO STUCKERT/iStock /Getty Images Plus

Learning Outcomes

After reading this chapter, you should be able to

• Describe the components of the ecological hierarchy. • Identify characteristics of all ecosystems. • Explain how energy flows through ecosystems. • Describe how matter cycles in ecosystems. • Explain how and why eutrophication occurs. • Describe the importance of biodiversity and the major threats to it. • Discuss what is being done to address threats to biodiversity. • Define the term planetary boundaries.

Section 2.1 The Earth as a System

The environment and the study of the environment encompass everything that surrounds us, including all living and nonliving things. Ecology is the study of the relationships and interac- tions between living organisms and their surrounding environment. The term ecology derives from the Greek word for “house” or “dwelling,” oikos, and “study,” or logy. In other words, ecol- ogy is the “study of our house,” and it is at the core of what environmental science is about.

The goal of this chapter is to give you a foundation in some key ecological concepts that will be important to studying environmental issues in subsequent chapters. The chapter starts by introducing the idea of the Earth as a system and how ecologists and environmental sci- entists use a “systems view” or “systems thinking” in the work they do. We will then focus on the study of the environment at the ecosystem scale, considering what ecosystems are, how they are defined, and what some of their key characteristics are. We will review two funda- mental ecosystem processes—energy flow and matter cycling—that play a central role in understanding environmental issues.

We then shift to the concept of biodiversity: what it means, why it matters, and what are the major threats to it. The chapter concludes with a brief discussion of an interesting concept known as planetary boundaries. These boundaries were developed as a way to help us think of the planet’s overall health and to warn us when our actions might be jeopardizing the environment we all depend on. If we think of ecology as the study of our “house,” planetary boundaries are a way for us to monitor and stay aware of threats or dangers to the planet we all call home.

2.1 The Earth as a System

Throughout this book, and in the study of environmental science, you will frequently hear the environment described as a system or as being composed of numerous, interconnected systems. What does this mean, and why does it help to think about the environment in terms of systems?

A system can be defined as a set of connected or interdependent things that together form a more complex whole. For example, the car you drive is made up of multiple, interacting sys- tems that work together to provide you with mobility. These include the ignition, electrical, braking, steering, cooling, and suspension systems. Likewise, a rain forest in Borneo, a wet- land along the Gulf Coast, a mountain stream in the Rockies, or a grassland in the upper Mid- west can all be thought of as systems (in this case, ecosystems). Forests, wetlands, streams, grasslands, and other ecosystems all consist of organisms and elements that are interdepen- dent and that together make up a more complex whole.

Given the sheer complexity of the Earth as a system, ecologists and environmental scien- tists find it helpful to view and study the world at different scales. They do this through an approach known as the ecological hierarchy theory. The ecological hierarchy illustrates the relationships between different organisms and organizes those relationships into different levels.

Section 2.1 The Earth as a System

At the first level of the ecological hierarchy are individual organisms, such as a single elephant or bird. Multiple individuals of the same species living in a particular location, such as a herd of elephants or a flock of birds, are considered a population, the second level of the ecologi- cal hierarchy. A group of populations of different species that interact and live in the same place—such as a forest, stream, or wetland—is known as a community, the third level of the ecological hierarchy. This community and its physical environment make up the next level, an ecosystem. In other words, ecosystems include the living, or biotic, communities that occupy them, as well as the nonliving, or abiotic, characteristics that often shape the abundance and diversity of life in that location. Different ecosystems connect and interact with one another— for example, a forest ecosystem connects with the stream ecosystem that runs through it— and make up a landscape. At an even larger scale, or higher level, ecosystems and landscapes that have similar climate and vegetation can be grouped into biomes (see Figure 2.1). Gener- ally speaking, tropical regions characterized by warm temperatures, an abundance of mois- ture, and relatively constant levels of daylight contain the biomes with the highest number and diversity of organisms.

Figure 2.1: Biomes

Earth’s major biomes result primarily from differences in climate. Each biome contains many ecosystems made up of species adapted for life in their specific biome.

Adapted from “Global Soil Regions Map,” by U.S. Department of Agriculture Natural Resources Conservation Service, 2005 (http://www .nrcs.usda.gov/wps/portal/nrcs/detail/soils/use/worldsoils/?cid=nrcs142p2_054013).

Equator

Tropic of Capricorn

Tropic of Cancer

30° S

30° N

Tropical forest

Temperate deciduous forest

Savanna

Temperate grassland

Desert

Coniferous forest

Chaparral

Tundra (arctic and alpine)

Oceans

Polar and high- mountain ice

http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/use/worldsoils/?cid=nrcs142p2_054013

Section 2.1 The Earth as a System

Let’s use an example to illustrate the ecological hierarchy at work (see Figure 2.2). We’ll start with a single bird common to our state of Pennsylvania, the wood thrush. A certain population of wood thrushes breeds and reproduces in a specific forested region near the home of one of the authors. That population of wood thrushes interacts with other populations of birds, mammals, insects, and plants at the community or biotic community scale. The biotic com- munity, combined with the abiotic or nonliving components, make up an ecosystem—in this case a forested ecosystem that the wood thrush favors as habitat. That forest is embedded in a larger landscape of rivers, streams, wetlands, and human-dominated land uses. The forests of Pennsylvania are similar to temperate forests in other regions of the United States and the world and make up part of the temperate forest biome.

Figure 2.2: The ecological hierarchy

The ecological hierarchy enables ecologists and environmental scientists to study the Earth at different scales.

PredatorsPredators

Population

Community

Ecosystem

Landscape

Biome

Individual

Section 2.1 The Earth as a System

At the highest scale, or level, the entire planet is made up of four separate but interact- ing realms or spheres (see Figure 2.3). These four spheres include the lithosphere (or geo- sphere), the hydrosphere, the atmosphere, and the biosphere. The lithosphere is the solid Earth, specifically the upper crust (extending up to 100 kilometers, or 62 miles, below the surface) and the uppermost mantle (extending as far as 2,500 kilometers, or 1,550 miles, below the surface). The hydrosphere is the watery parts of our planet: the oceans, rivers, lakes, clouds, groundwater reservoirs, and glaciers that cover three quarters of the Earth’s surface. The atmosphere is a mixture of gases, mostly nitrogen and oxygen, with smaller amounts of argon, carbon dioxide, and other trace gases. The atmosphere is held to the Earth’s surface by gravity and thins rapidly with altitude. Ninety-nine percent of the Earth’s

Figure 2.3: The four spheres

The highest scale, or level, of the ecological hierarchy is made up of four spheres. Environmental scientists study interactions among the atmosphere, lithosphere, and hydrosphere. The biosphere is the zone of all three spheres that contains life.

Hydrosphere (water)

Lithosphere (earth)

Atmosphere (air)

Biosphere

Section 2.2 Ecosystems as a Concept

atmosphere is concentrated in the first 30 kilometers (19 miles), but a few traces of atmo- spheric gases remain even in frigid, near-space conditions thousands of kilometers above the Earth’s surface. The biosphere is the zone where life exists on Earth. Most life concentrates at or near the surface of the land and ocean, but some bacteria thrive in rocks 4 kilometers (2.5 miles) beneath the surface, some organisms live in deep ocean trenches, and a few windblown microorganisms drift in thin, cold, inhospitable air waves 10 kilometers (6 miles) above the surface. Most of this book will focus on issues and conditions that occur in the biosphere, but we will also examine the lithosphere (energy resources), the hydrosphere (freshwater and ocean resources), and the atmosphere (climate change, air pollution, and ozone depletion).

The concepts of the ecological hierarchy and the four spheres allow us to take something as vast and complex as the entire planet and view it at many different scales. A systems view or systems thinking helps us see how the pieces within each level connect and interact. Systems thinking is an approach to science that considers not just the individual parts of a system but also how they interact and interrelate over time. When we think of the environment as a system, we become more aware of how our actions in one place might have consequences in another. The late ecologist Barry Commoner (1971) summed this up in his first law of ecol- ogy: Everything is connected to everything else.

Section 2.2 will home in on one level of the ecological hierarchy—the ecosystem. Much of the work done by ecologists and environmental scientists is at the ecosystem scale, and so it is important to better define and understand what ecosystems are and how they operate.

2.2 Ecosystems as a Concept

Section 2.1 described ecosystems as a collection of living (biotic) and nonliving (abiotic) enti- ties that exist and interact in a particular location and time. For example, the forest ecosystem that is home to the wood thrush is made up of birds, insects, mammals, amphibians, fungi, trees and plants, soils, rocks, and nutrients. Forests and other ecosystems are characterized by a number of factors that are the focus of this section.

Ecosystems Are Open Virtually all of the Earth’s ecosystems are open systems, meaning that they receive inputs from surrounding systems and produce outputs. Some of ecosystems’ most important inputs and outputs come in the form of energy and matter, which will be described in much greater detail in Section 2.3. For now, it’s enough to visualize an ecosystem in much the same way you might view your home, as an open system that relies on inputs of food, energy, and water while pro- ducing outputs like solid waste, wastewater, and emissions of air pollutants. Ecologists refer to the energy and matter that flow into, through, and out of an ecosystem as throughput.

Section 2.2 Ecosystems as a Concept

Ecosystems Are Subject to Feedback Loops As energy and matter flow into and out of ecosystems, and as ecosystems are subject to various kinds of disturbance and change, we often see what are known as feedback loops. A positive feedback loop causes the system to keep changing further in the same direc- tion. A negative feedback loop causes the system to change in the opposite direction.

In nature, a positive feedback loop might occur when a section of a forest is clear-cut, creating light and temperature conditions along the new forest edge that lead to even further loss of trees and worsening defores- tation. A negative feedback loop might occur if there were a sudden increase in the popu- lation of a certain insect species. This might lead to an equivalent increase in the population of birds and other organisms that prey on or eat that insect, returning the insect population to what it was originally. Positive feedback loops tend to be destabilizing, resulting in continual change, while negative feedback loops tend to be self-correcting or stabilizing.

In other words, don’t think of positive feedback loops as “good” or negative feedback loops as “bad.” In fact, the opposite is generally the case. Most systems in nature are characterized by negative feedback loops, which result in a dynamic equilibrium or homeostasis—the ten- dency of a system to maintain relatively stable conditions over time.

When a system is experiencing a series of positive feedback loops, changing further and fur- ther in the same direction, it’s possible that it could reach a threshold or tipping point. When this happens, the system collapses or shifts to a new, different state. For example, when water is boiled to a tipping point of 100 °C (212 °F), it turns to vapor. When water is cooled to 0 °C (32 °F), it turns to ice.

A potential tipping point that worries many environmental and climate scientists involves a positive feedback loop from melting permafrost areas in the Arctic. This will be explained in more detail in Chapter 8, but basically, permafrost soils hold large quantities of methane and carbon, which can become carbon dioxide as these soils thaw. Human activities like burning fossil fuels are already raising methane and carbon dioxide levels in the atmosphere. Meth- ane and carbon dioxide are greenhouse gases that trap heat in the atmosphere, and this is increasing temperatures in the Arctic. As temperatures increase, permafrost soils begin to thaw and release more methane and carbon dioxide into the atmosphere. This methane and carbon dioxide leads to further warming and more thawing of permafrost soils, which results in even greater releases of methane and carbon dioxide, and so on. Such a situation could lead to rapid and runaway global warming and climate change, pushing our planet beyond a threshold and over a tipping point.

luoman/E+/Getty Images Clear-cutting forest can create conditions that lead to further deforestation—an example of a positive feedback loop.

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

Ecosystems Provide a Range of Conditions For a wood thrush to survive in the forested ecosystem in Pennsylvania, it requires certain resources and conditions such as food, water, and reasonable temperatures. When these envi- ronmental factors and conditions are present in a way that is most favorable for the wood thrush, they are said to be in the optimal range. The entire range over which the wood thrush could survive, even if it did not thrive in an optimal sense, is known as the range of toler- ance, with the extreme ends of that range known as the limits of tolerance. Conditions that fall between the optimal range and the limits of tolerance are known as zones of stress because organisms experience increasing stress the further they are from their optimal range.

All living organisms have an optimal range, zones of stress, and limits of tolerance for every abiotic factor they depend on, and these are different for different species. Some species have a very broad optimal range and can tolerate a wide variety of conditions, while other species are more sensitive and have optimal ranges that are narrow. Ecologists refer to a factor that limits growth as a limiting factor, meaning that even if other factors and conditions are pres- ent in optimal amounts, the absence or shortage of a limiting factor will stress organisms that depend on it. For example, you can give a plant all the water and nutrients you want, but if there is not enough light, the plant will be limited in its growth. Lastly, we generally find that certain species, like the wood thrush, are present in specific habitats, like a temperate forest. Within that forest, the wood thrush occupies a specific ecological niche, the combination of conditions and resources needed for it to live. Different species can occupy the same habitat but have very different niches. Different bird species in the same forest habitat can nest in different places, eat different foods, eat at different times of day, and have other differences in their ecological niche that limits competition between them.

2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

Despite the range of conditions that characterize the ecosystems found in different biomes around the world, all these ecosystems have something in common. With few exceptions, Earth’s ecosystems are powered by solar energy, and the organisms within those ecosystems depend on matter in the form of nutrients, water, oxygen, and other gases to survive. This sec- tion reviews two fundamental ecosystem processes that will help you better understand life on Earth: energy flow through ecosystems and matter cycling in ecosystems.

Energy Flow Through Ecosystems The most basic definition of energy is the capacity or ability to do work. In ecology, the term energy is usually used to define the ability of organisms to do biological work, such as moving, growing, eating, or reproducing. Scientists further divide energy into two basic forms: kinetic and potential. Kinetic energy is energy in motion, while potential energy is stored energy. The image of a dam is often used to illustrate the difference between these two types of energy.

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

By holding moving water back, a dam is cre- ating a reservoir, which represents accumu- lated or potential energy. When the gates of the dam are opened and the water starts to move again, that potential energy is con- verted to kinetic energy. Likewise, gasoline represents a type of potential energy, stored in the chemical bonds among the atoms that compose it. When that gasoline is ignited in the engine of a car, the potential energy held in those chemical bonds is released and converted to the kinetic energy of motion.

Laws of Thermodynamics There are two fundamental laws or prin- ciples that apply to energy. The first law of thermodynamics (also known as the law

of conservation of energy) states that energy can change from one form to another but can- not be created or destroyed. When we burn gasoline in a car engine, we are converting that chemical energy to the energy of motion and heat, but we end up with the same amount of energy. The second law of thermodynamics states that even though the overall amount of energy is conserved, energy conversion will always change that energy from a more useful to a less useful state. Gasoline is a highly useful form of energy because small quantities of it contain great potential to do work, but once combusted it changes to mostly heat energy that is too diffuse to be useful. This tendency for energy to move from a more useful state to a less useful state is known as entropy. An important implication of the laws of thermodynamics is that energy conversions tend to be inefficient. Only a small portion of the chemical energy stored in gasoline (typically 15%–25%) is actually converted to mechanical energy.

If every energy conversion moves us from a more useful state to a less useful state, we would appear to be doomed to a world of increasing disorder. Yet in the world around us, we see many signs of increasing order—for example, humans, animals, plants, and other organisms being born and growing. So how can this be? The answer lies in the fact that the Earth is an open system subject to inputs of solar energy. That incoming solar (light) energy drives pro- cesses that create new stores of potential energy that fuel virtually all the Earth’s ecosystems.

Fuel for Life Most living systems and organisms on the planet are ultimately powered by energy from the sun. The starting point is a group of organisms known as autotrophs or primary produc- ers: mostly plants, algae, and some types of bacteria. Primary producers take the building blocks of carbon dioxide and water and produce sugar (glucose) molecules with high poten- tial energy content. Primary producers do this through a process known as photosynthesis. Photosynthesis is driven by light energy from the sun, as illustrated in Figure 2.4.

Jupiterimages/Stockbyte/Thinkstock A dam represents the difference between kinetic and potential energy. Water held by the dam in a reservoir is potential (stored) energy. When the water is released by opening the gates of the dam, it turns into kinetic energy.

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

The ability of plants and other primary producers to do photosynthesis is really the foun- dation for life on Earth as we know it. Photosynthesis starts with chlorophyll, which gives plants their green color. Chlorophyll absorbs light energy from the sun and uses it to remove hydrogen atoms from water (H2O) molecules. The hydrogen is combined with carbon atoms from carbon dioxide (CO2) to form long chains of glucose molecules, or sugar (C6H12O6). One by-product of photosynthesis is oxygen (O2) released to the atmosphere, and this is another way plants and other primary producers can be seen as essential to life as we know it: Plants are sometimes referred to as “the lungs of the planet.” The process of photosynthesis can be summarized in an equation:

6CO2 (carbon dioxide) + 6H2O (water) + light energy = C6H12O6 (glucose) + 6O2 (oxygen)

Glucose molecules produced through photosynthesis represent a form of high-quality poten- tial energy. This energy can be used by primary producers for their own biological functions as well as by other organisms that consume the primary producers. Plants use glucose to build stems, roots, fruit, leaves, and other structural elements. Plants also store glucose for future

Figure 2.4: Photosynthesis

Producers use photosynthesis to convert the basic building blocks of sunlight, carbon dioxide, and water into energy other organisms can use.

Sunlight

Carbon dioxide

Water

Minerals

Oxygen

Sugar

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

use and to power a process known as cellular respiration. Cellular respiration allows the plant to utilize the potential energy stored in glucose to perform the biochemical processes it needs to grow and survive. Cellular respiration is essentially photosynthesis in reverse:

C6H12O6 (glucose) + 6O2 (oxygen) = 6CO2 (carbon dioxide) + 6H2O (water) + energy

Some of the potential energy that is stored in plants as glucose is also available to other organ- isms that eat either plants or the animals that eat plants. Just as with plants, these animals use respiration to “burn” the energy stored in the glucose molecules, in the process releasing low-quality heat energy. You can see why energy is described as flowing through ecosystems. Energy enters the system as sunlight and is converted to high-quality potential energy in the form of glucose, utilized by organisms in the environment through respiration, and released as energy that dissipates back into space.

Chains of Energy Ecologists use the concepts of producers, consumers, and decomposers to describe the flow of energy through an ecosystem. As discussed earlier, autotrophs like plants and algae are pro- ducers because they are able to manufacture glucose through the process of photosynthesis. The entire amount of potential energy produced by plants in a given ecosystem is referred to as gross primary production. Because plants use much of this energy for their own biochemi- cal needs, the energy that is “left over” for other organisms is called net primary production.

The organisms that rely on plants for some of that “leftover” energy are known as consum- ers. A rabbit that eats grass in an open meadow would be considered a primary consumer, whereas a snake that eats the rabbit would be considered a secondary consumer. A hawk that eats the snake would be considered a tertiary consumer. All of these consumers are known as heterotrophs. Recall that primary producers are referred to as autotrophs, meaning they can produce their own food (auto = “self”; troph = “nourish”). In contrast, heterotrophs refers to organisms that rely on other organisms for their food (hetero = “other”; troph = “nourish”). While primary consumers are herbivores (plant eaters), secondary and tertiary consumers can be either carnivores (which eat other animals) or omnivores (which eat both plants and other animals).

Last but not least are what are known as decomposers. Decomposers break down dead organic material, whether plants or animals, to obtain the energy and nutrients they need. Also known as saprotrophs (sapro = “rotten”; troph = “nourish”), decomposers include bacte- ria and fungi like mushrooms, as well as scavenging animals like vultures and hyenas. Decom- posers play a critical but often overlooked role in breaking down dead organic material and releasing important nutrients that can be reused by producers for a new round of growth.

Energy flows in an ecosystem through food chains—for example, the hawk that ate the snake that ate the rabbit that ate the grass. In other words, food chains describe simple, linear feeding relationships among organisms. Ecosystems are characterized by many different food chains that combined make up a food web, which describes the many feeding relationships in a community (see Figure 2.5).

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

One important characteristic of food chains and food webs is that primary producers are far more abundant than primary consumers, and primary consumers are more abundant than secondary consumers, and so on. Ecologists use the concept of trophic levels to explain this. Each link in a food chain is considered a trophic level, and as we move from one trophic level to the next, we lose energy because of the second law of thermodynamics. As a result, tro- phic levels in ecosystems tend to be characterized by a pyramid shape, with large numbers of organisms at lower trophic levels and few at the top (see Figure 2.6). On average, ecolo- gists estimate that only about 10% of the energy consumed at one trophic level is available

Figure 2.5: Food web

Energy flows in an ecosystem through the food web.

Bald eagles Salmon

Birds

Rabbits Snakes

Mice

Insects Grasses and plant material

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

to the next level. In other words, 10,000 pounds of grass in a meadow might only support 1,000 pounds of rabbits, which could support 100 pounds of snakes, which could support 10 pounds of hawks. As a result, most food chains are typically characterized by only three or four trophic levels.

Figure 2.6: Trophic levels

Energy enters an ecosystem through an external source (the sun) and flows through the progressive trophic levels of a food chain. On average, about 10% of the net energy produced at one trophic level is passed on to the next level; the rest is lost as heat energy.

Solar energy

Tertiary consumers

Secondary consumers (animals that feed on herbivores)

Primary consumers (animals that feed on plants)

Heat lost

Primary producers (plants, algae, and some bacteria)

Decomposers

Matter Cycling in Ecosystems The previous section described how energy tends to flow through ecosystems, entering as sunlight and leaving as heat. In contrast, water and chemical elements such as carbon, nitro- gen, and phosphorous tend to cycle in ecosystems. Scientists who study such cycles, known as biogeochemical cycles, know that the same atom of carbon used by a tree outside your window for photosynthesis may have been exhaled by a human or animal thousands of years

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

ago. This is because of the law of conservation of matter, which holds that matter can nei- ther be created nor destroyed. If you look back at the chemical reactions for photosynthesis and respiration, you will see that the carbon, oxygen, and hydrogen take different forms but are always present in the same quantities on both sides of the equation.

This principle of conservation of matter was summed up by the late ecologist Barry Com- moner (1971) as “everything must go somewhere,” or “there is no away” (p. 39). When we burn fossil fuels like oil and coal, which contain mostly carbon, we are moving that carbon from one place (the deep Earth), where it had been buried for millions of years, and put- ting it another place (in this case the atmosphere as carbon dioxide). When we mine phos- phate deposits to make fertilizer and some of that fertilizer runs into streams and rivers, we are moving phosphorous from one place to another, but it does not go away. The rest of this section will review three critical biogeochemical cycles: carbon, phosphorous, and nitrogen. (The water cycle will be explained in Chapter 5).

The Carbon Cycle Carbon is a basic building block of organic compounds required for life. Carbon circu- lates through the biosphere, atmosphere, and hydrosphere and is stored in under- ground deposits in the lithosphere. Figure 2.7 is a basic illustration of the carbon cycle, showing carbon flows from one reservoir of carbon to another. Recall that carbon in the atmosphere—in the form of carbon dioxide—is utilized by plants for photosyn- thesis. Some of that carbon is used to build plant tissue, and some of the plant tissue is eaten by animals and converted into their own tissue. Both plants and animals respire, returning some of that carbon to the atmo- sphere. As animals and plants die, the car- bon in their tissue is deposited in the soil, where some is consumed and respired back to the atmosphere by decomposers. Some of the carbon dioxide in the atmosphere is also dissolved in the ocean, where it can be utilized by marine algae and plankton before being deposited in sediments at the bottom of the ocean for long periods.

Human activities are having a serious impact on the carbon cycle. Over millions of years, car- bon stored in deposits of dead plant and animal tissue has been converted through geologic processes to fossil fuels like coal, oil, and natural gas (more on this in Chapter 7). Since the start of the Industrial Revolution, we have dug and pumped massive amounts of these fuels from the ground and burned them, taking carbon that was in the ground for millions of years and adding it to the atmosphere over just a short period of time. Because we are adding car- bon to the atmosphere faster than it can be removed, atmospheric concentrations of carbon dioxide have increased from roughly 270 ppm a century ago to over 400 ppm today (Lindsey,

Rasica/iStock/Thinkstock Since the Industrial Revolution, humans have added enormous amounts of carbon dioxide to the atmosphere through our heavy use of coal, oil, and natural gas.

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

2018a). Because carbon dioxide is a powerful greenhouse gas in the atmosphere, these higher concentrations are a big reason for global climate change. In addition to burning fossil fuels, other human activities like clearing and burning forests and other vegetation are also adding large amounts of carbon to the atmosphere and altering the global carbon cycle.

Figure 2.7: The carbon cycle

In the carbon cycle, carbon circulates from one pool to another. The scale of human activities — represented here by red arrows—has disrupted that natural cycle and equilibrium.

Ocean carbon uptake

Fossil fuels

Decomposers

Sunlight

Photosynthesis

Auto and factory

emissions

Animal respiration

CO2

Plant respiration

Deforestation Dead organisms

and waste products

The Phosphorous Cycle Phosphorous is an important nutrient for life and is considered a limiting factor in many ecosystems. The major reservoir for this nutrient is phosphate rock or ore. These ores have accumulated over thousands of years and are brought to the Earth’s surface through geologi- cal uplifting of deep ocean sediment. As these rocks are exposed to rain and other elements, they gradually break down, releasing inorganic phosphate ions. These phosphate ions are carried by water into the soil, where they can either be absorbed by plant roots and utilized as an important nutrient for plant growth or washed out into the oceans, where over time they become part of deep ocean sediments once again. Organic phosphate in plants can be available to primary consumers that eat the plants, as well as secondary consumers and so

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

on through ecosystem food webs. As plants and animals die, decomposers break down their tissue and make phosphorous available again for new plant growth.

Phosphorous is considered a limiting factor or limiting nutrient because most soils contain little phosphate. Because of this, large deposits of phosphorous are mined around the world and incorporated into fertilizers to help promote plant growth. Much of the phosphorous in fertilizer runs off of farm fields and makes its way into streams, rivers, and ultimately the ocean, where it can lead to a serious water pollution problem known as eutrophication (see the case study in Section 2.4). The phosphorous fertilizer that gets taken up by crops ends up being eaten by the animals that eat those plants—usually humans, cows, pigs, or chickens. These animals’ waste products also contain some of that phosphorous (remember, there is no away!), and this waste can also find its way into bodies of water and add to the eutrophication problem.

The Nitrogen Cycle Like phosphorous, nitrogen is also a critical nutrient for all forms of life and can act as a limiting factor in plant growth. The largest pool or reservoir of nitrogen on the planet is air (see Figure 2.8), with nitrogen making up 78% of the volume of the atmosphere. Despite this abundance, plants cannot make use of atmospheric or nonreactive nitrogen. In nature, nitro- gen becomes available to plants through two processes: electrical storms and biological fixa- tion by bacteria. The sheer energy of a lightning bolt is enough to break a nonreactive nitro- gen molecule (N2) into two, where N can combine with oxygen to produce nitrogen oxides. These wash out in rain as nitrates and become available to plants for growth. Certain types of soil bacteria are also able to convert nonreactive nitrogen in the air to a usable form through a process known as nitrogen fixation. Some of these bacteria live on the roots of certain plants known as legumes (for example, beans and peas) and exist in a form of symbiosis, whereby the plants provide what the bacteria need and the bacteria provide for the plant. Symbiosis is a close biological interaction between two organisms.

Human modification of the nitrogen cycle occurs because we use industrial processes to remove nitrogen from the atmosphere and turn it into nitrogen fertilizer. This is known as industrial nitrogen fixation, and it requires tremendous amounts of energy to accomplish. Nonreactive nitrogen is removed from the air and combined with hydrogen (usually derived from natural gas) to make ammonia-based fertilizers. As with phosphorous, nitrogen fertil- izers are added to farm fields to promote plant growth. And as with phosphorous, nitrogen fertilizers run off into bodies of water and contribute to the pollution problem known as eutrophication.

The carbon, phosphorous, and nitrogen cycles show that matter is cycled in natural systems. In contrast, energy flows into, through, and out of ecosystems. Energy enters the system as sunlight and powers photosynthesis as the basis for most life on the planet. The energy pro- duced by photosynthesis is released as heat or waste energy as plants consume their own stored energy, animals consume plants, and other animals eat those animals. Matter in the form of water, carbon, phosphorous, nitrogen, and other nutrients is taken up by plants and enters food webs, where it generally cycles back to be used again.

Section 2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling

Human interactions in these systems tend to disrupt the cyclical processes and replace them with linear ones. We mine phosphorous and use industrial processes to produce nitrogen, which is added to farm fields to promote plant growth. These nutrients enter other systems, where they can create the pollution problems described in Section 2.4. We then mine and produce more fertilizer and repeat the same process. This approach is not sustainable. One of the biggest challenges in moving from our current systems of economic production to more sustainable systems is to try to mimic or copy the cyclical models we find in nature.

Figure 2.8: The nitrogen cycle

Nitrogen circulates from the environment to living organisms and back to the environment. This cycle involves nitrogen-fixing bacteria, which convert nitrogen into forms usable by living organisms, and denitrifying bacteria, which break down nitrogen compounds and return gaseous nitrogen to the atmosphere.

Atmospheric nitrogen

Electrical storms

Plant proteins

eaten

Decaying organic matter

Ammonia (NH4), nitrate (NO3) and other nitrogen compounds

Denitrifying bacteria

Nitrogen-fixing bacteria (fixation)

Excretion Assimilation & absorption

by plants

Section 2.4 Case Study: Eutrophication in the Gulf of Mexico

2.4 Case Study: Eutrophication in the Gulf of Mexico

Recall from Section 2.3 that both nitrogen and phosphorous are considered limiting factors or limiting nutrients in most ecosystems. In other words, even if other conditions are favor- able for plant growth and other life, the absence or scarcity of nitrogen and phosphorous will limit overall growth. Because this nutrient limitation is true of most farmland, nitrogen and phosphorous are widely applied as fertilizers in commercial farm operations around the world. When some of those fertilizers get washed off of fields and into rivers, streams, lakes, and oceans, it can cause a water pollution problem known as eutrophication. Eutrophication leads to sharp declines in dissolved oxygen levels in bodies of water, and this can kill off fish and other marine life. The result is what ecologists refer to as a dead zone.

Defining Eutrophication What is eutrophication, and why would something “good” (like fertilizer) lead to something “bad” like dead zones? The answer lies in the fact that nitrogen and phosphorous are also limiting nutrients in aquatic (water-based) ecosystems. When excess nitrogen or phosphorous enters a body of water like the Gulf of Mexico, it “fertilizes” and promotes the rapid growth of plantlike phytoplankton (algae and cya- nobacteria), commonly referred to as an algae bloom. Under normal conditions, phytoplankton can be a source of food for other marine life, but when eutrophication occurs, the organisms that typically con- sume phytoplankton can’t keep up. This leads to large quantities of phytoplankton eventually dying and sinking to the bottom, where they are decomposed by other bacteria. These bacteria use dissolved oxygen in the water as part of the decomposition process, and this results in sharp declines in oxygen levels. Low oxygen levels can lead to the death and displacement of all kinds of marine life, resulting in dead zones.

Examining the Problem in the Gulf Aquatic dead zones can be found in many parts of the world. Environmental scientists esti- mate that there are over 400 dead zones globally (Diaz & Rosenberg, 2008). In the United States the Gulf of Mexico dead zone is considered the largest, and this has a lot to do with geography. The Gulf of Mexico receives all the water drained from the Mississippi River, and the Mississippi alone drains over 40% of the surface area of the lower 48 states. The Mis- sissippi River basin also includes much of the largest agricultural production areas in the country, where large amounts of nitrogen and phosphorous fertilizers are applied to fields of

Patrick Semansky/Associated Press Dead fish in the Gulf of Mexico off the Louisiana coast. Fertilizers that wash into bodies of water can cause negative impacts such as algae blooms, eutrophication, and dead zones.

Section 2.4 Case Study: Eutrophication in the Gulf of Mexico

corn, soybeans, and other commodity crops. Some of the largest animal feedlots and produc- tion areas (beef, chicken, and pork, in particular) in the United States are also located in the Mississippi River basin, and the waste products from these animals contain large quantities of nitrogen and phosphorous. When people eat crops grown with nitrogen and phosphorous or eat animals that were fed those crops, they also take in and eventually release most of those nutrients through their waste. Municipal sewage treatment plants strive to remove as much of this nitrogen and phosphorous as possible, but older systems are not very effective at this. Lastly, common fertilizers applied to lawns, gardens, and golf courses also contain nitrogen and phosphorous. All of these sources can add nutrients that run off into nearby bodies of water before being washed down to the sea.

Eutrophication is a regular seasonal occurrence in the Gulf of Mexico. Spring rains and snow- melt coincide with large applications of fertilizer at the start of the growing season. By early summer, hypoxic or low-oxygen conditions start to appear in the Gulf and typically worsen as the summer goes on. Eventually, seasonal storms, including hurricanes, help mix the water in the Gulf and return oxygen to hypoxic areas. Years that are characterized by heavy rains in the upper Midwest and higher river flows in the Mississippi usually result in larger dead zones. In contrast, the Gulf of Mexico dead zone typically shrinks in years of drought. Scientists have been measuring oxygen levels and hypoxic conditions in the Gulf of Mexico since 1985, and the largest annual dead zone ever recorded was in the summer of 2017. That year the Gulf dead zone measured close to 23,300 square kilometers (9,000 square miles), roughly the size of New Jersey (National Oceanic and Atmospheric Administration, 2017).

Applying Our Knowledge We can use the case study of the Gulf of Mexico dead zone to see how some of the terms and concepts introduced earlier in this chapter apply to the study of ecology and environmental science. First, we need to view the dead zone problem at the landscape level, since it involves connections between many different ecosystems on land and in the water. To understand what was causing the dead zone and what to do about it, scientists needed to apply systems thinking, rather than just looking at one piece of the puzzle. The Gulf of Mexico clearly represents an open system receiving inputs of nitrogen and phosphorous from other systems. Phytoplank- ton blooms can set off short-term positive feedback loops as declining oxygen levels drive away organisms that might feed on and control the population of phytoplankton. As oxygen levels drop, marine life moves further away from the optimal range and toward the limits of tolerance, sometimes resulting in reproductive failure, migration, and death (all examples of stress). A tipping point can be reached at which most marine life cannot survive in that area.

The dead zone problem is triggered by nitrogen and phosphorous, which are limiting factors introduced to the Gulf ecosystem by human activities. The movement of these nutrients from farms, feedlots, golf courses, lawns, and sewage treatment plants to the Gulf of Mexico is an example of the law of conservation of matter and the cycling of matter. In the words of Com- moner, everything is connected to everything else, everything must go somewhere, and there is no away. Lastly, this case study further illustrates how linear human systems are compared to the kinds of cyclical systems we see in nature. We mine phosphorous from the ground or extract nitrogen from the atmosphere at great cost. We apply these to crops and feed the

Section 2.5 What Is Biodiversity, and Why Does It Matter?

crops to animals. We eat the animals, and the nitrogen and phosphorus pollution from fer- tilizer runoff, animal waste, and our own waste makes its way to the Gulf of Mexico, where it triggers an environmental catastrophe. We then mine more phosphorous, produce more nitrogen, and start the process all over again.

Even though dead zones of a smaller size can occur naturally under certain conditions, the size, scale, and regularity of the dead zones in the Gulf of Mexico and over 400 other regions of the world can be interpreted as a giant “check engine” light. Something is wrong with the way we are currently managing our agricultural, water, and energy resources. The specifics of what is wrong, as well as what can be done to correct the situation, will be the focus of later chapters.

2.5 What Is Biodiversity, and Why Does It Matter?

Up to this point, the chapter has mostly discussed nature and natural systems in technical terms relating to ecosystems, matter, and energy. The Gulf of Mexico case study helped illus- trate how those terms apply to a specific environmental problem. But the more important goal of providing this foundational knowledge is to enable you to more fully explore the criti- cal concept of biodiversity. When human activities disrupt ecosystems, as well as energy flow and matter cycling in those ecosystems, biodiversity suffers; as a result, human well-being suffers too.

As discussed in Chapter 1, biodiversity is a measure of the variety of life and organisms in a specific ecosystem. The overall biodiversity on planet Earth is truly amazing. Some biologists estimate that there may be as many as 100 million species on the planet, although most esti- mates range from 7 million to 10 million (Zimmer, 2011). Of that total, only about 2 million species have been identified to date, suggesting that there is still much we do not understand or appreciate about the diversity of life on Earth. This section will further define and explore biodiversity and why biodiversity is so important. Section 2.6 will review some of the major threats to biodiversity around the world and what is being done to address them.

How Ecologists Characterize and Measure Biodiversity Ecologists typically characterize biodiversity in four different ways. First, and most com- mon, is to measure biodiversity in terms of species diversity, or the number of different species and their relative abundance in a given ecologic community. As previously discussed, species diversity tends to be highest in the tropical regions of the world and decline toward polar regions. In addition, hundreds of scientific studies conducted in different regions of the world have demonstrated that higher rates of species diversity are associated with both increased productivity in ecosystems and greater resilience in response to stress (Tilman, Isbell, & Cowles, 2014). For more on this issue, see Apply Your Knowledge: How Does Biodiver- sity Improve Ecological Resilience?.

Second, genetic diversity refers to the variety of genes and genetic material found within a population or species. Generally, the more genetically diverse a population is, the better

Section 2.5 What Is Biodiversity, and Why Does It Matter?

Apply Your Knowledge: How Does Biodiversity Improve Ecological Resilience?

Michigan’s Isle Royale is a 72-kilometer-long (45-mile-long) island located near the Canadian border in Lake Superior. Due to its unique location, the island remains somewhat isolated from the U.S. and Canadian mainland, and researchers use its relatively simple ecosystem to study several North American species interactions. Taking a closer look at the flora and fauna on Isle Royale can help us understand how biodiversity can make ecosystems more resilient.

Isle Royale hosts a variety of familiar North American species, many of which traveled to the island by air, water, and ice long ago. A mix of coniferous and deciduous trees supports primary consumers like squirrels, hares, birds, and moose. In marshy areas, aquatic plants provide food and habitat for beavers, fish, and aquatic insects. Foxes eat some of the smaller critters on Isle Royale, but the top of the food chain is occupied by wolves. Wolves are the only creatures that regularly prey on the formidable moose populations inhabiting the island.

A simplified food web in Figure 2.9 highlights some of the major species interactions on Isle Royale. Take a moment to study this ecosystem and consider the variety of ways that these organisms depend on one another.

(continued)

the chance that population will survive and adapt to environmental changes. This is because increased genetic diversity improves the likelihood that some members of a population will have genetic traits that enable them to withstand disease, drought, or some other form of stress. Those individuals are then able to pass along those genetic traits to future genera- tions. Genetic diversity can be viewed in much the same way that investors approach port- folio diversity. By not “putting all their eggs in one basket,” they are able to maintain their portfolio even if some of their investments do not do well.

A third way to think of biodiversity is in terms of ecosystem diversity. Ecosystem diversity refers to the different types of ecosystems—forests, wetlands, grasslands, and so on—found around the world. Because different ecosystems support different assemblages of species, it’s generally the case that higher rates of ecosystem diversity will result in greater species diver- sity. Different ecosystems provide us with different types and forms of critical ecosystem ser- vices. Recall from Chapter 1 that ecosystem services are life-supporting services provided by the natural capital or natural infrastructure of ecosystems. These include water filtration and nutrient cycling. Higher rates of ecosystem diversity result in a greater variety and volume of ecosystem services provided to us by natural systems.

Lastly, ecologists use the term functional diversity to describe all of the different ways in which organisms interact with and make use of a specific ecosystem. It’s generally the case that an ecosystem with high levels of species diversity will also be characterized by high rates of functional diversity. This is because different species obtain food, reproduce, use resources, and generate waste products in different ways. Understanding of functional diversity is important to the study of ecosystems and biodiversity because it provides greater insight into the actual behaviors and actions of different species and how they relate to one another within that ecosystem.

Section 2.5 What Is Biodiversity, and Why Does It Matter?

Apply Your Knowledge: How Does Biodiversity Improve Ecological Resilience? (continued)

Each species carries out vital functions for the larger ecosystem. Some organisms represent food sources for others. Some keep specific populations in check through hunting and consumption. Beavers engineer habitat, and ravens consume carrion and redistribute nutrients. Every one of these functions is essential to the larger ecosystem and the life that it supports.

In some cases there might be several species carrying out these ecosystem functions, and in other cases there might only be one or two. According to the food web in Figure 2.9, how many primary producers are providing food for primary consumers? How many predators are controlling the primary consumer populations through predation? Which of these two ecosystem functions will be more resilient if future environmental changes disrupt the ecosystem?

We can see from the food web that several forms of vegetation provide food sources for primary consumers. This gives us an idea of how this part of the ecosystem might respond to future changes. For example, if the balsam fir population was wiped out, the other forms of vegetation might still be able to provide suitable food and habitat for the ecosystem. In this example, the moose population appears to have several other food options.

The top of the food chain is a very different story. If wolves were to disappear, there would be no other species around to keep moose populations in check. This ecosystem function would go away completely, and it would dramatically impact the entire ecosystem.

A scenario like this occurred on Isle Royale in the 1970s, when humans introduced a disease that nearly wiped out the wolf population. The moose population exploded, leading to overgrazing and the destruction of forest habitat. With fewer moose kills to redistribute nutrients, forest soils also became less fertile. Before wolf populations could recover, a lack of forage and a rise in moose ticks led to a crash in the moose population. The entire Isle Royale ecosystem was thrown out of balance by just a single species, and populations are still recovering today.

Variety is a good thing for most ecosystems. If you have several species accomplishing a specific task, the ecosystem will be more able to cope with the loss of one or two of those species. Isle Royale has relatively low levels of species biodiversity, especially at the top of the food chain. As a result, the ecosystem underwent massive changes when a new disease was introduced.

Section 2.5 What Is Biodiversity, and Why Does It Matter?

How Biodiversity Occurs Ecologists attribute the amazing diversity of life on Earth to processes of natural selection and evo- lution. Natural selection refers to a process whereby individual organisms within a population are better able to survive because they possess certain genetic traits. These individuals will repro- duce and pass those traits on to their offspring. The result of natural selection is evolution, the process whereby the genetic makeup of populations of organisms changes gradually over time.

The combined processes of evolution through natural selection is widely accepted as scien- tific theory, in part because it can be observed happening in the world today. For example,

Apply Your Knowledge: How Does Biodiversity Improve Ecological Resilience? (continued)

Figure 2.9: Isle Royale food web

Removing one organism from an ecosystem’s food web can affect the entire ecosystem.

Adapted from Life: The Science of Biology (7th ed., Figure 55.7, Food Web of Isle Royale National Park), by W. K. Purves, D. E. Sadava, and G. H. Orians, 2004, Sunderland, MA: Sinauer Associates and W. H. Freeman. Copyright 2004 by Sinauer Associates, Inc., and W. H. Freeman & Co.

PineSpruce AshMaple Balsam �r Aspen, white birch

Snowshoe hare

Red fox

Red squirrel

Raven (scavenger)

Moose

Gray wolf

Section 2.5 What Is Biodiversity, and Why Does It Matter?

when farmers apply chemical insecticides to their fields to try to wipe out crop-destroying pests, they typically succeed in killing perhaps only 90%–95% of that population. This is because some individuals possess unique genetic traits that make them resistant to the insec- ticide. Those few survivors then reproduce and pass that resistance trait on to their offspring. After a few generations, the insect population begins to bounce back as the same insecticide proves less and less effective against the now resistant population (more on this problem in Chapter 4). Farmers then have to switch to a new insecticide or try something else to avoid having their crop destroyed.

An interesting form of evolution is what ecologists refer to as coevolution. Coevolution is defined as a process whereby two different species that interact closely, such as a predator species and a prey species, also evolve together in a series of genetic changes. Two examples will help illustrate coevolution. One involves a coevolutionary process that benefits both spe- cies (that is, it’s mutually beneficial). In the other, coevolution occurs as one species seeks an advantage over the other.

In the first case, there are a number of examples of tropical fruit–bearing trees coevolving with fruit-eating birds to the benefit of both. These trees have evolved to grow brightly col- ored and easy-to-see fruits that are also relatively odorless (to avoid attracting insects). These fruits tend to be difficult to eat “on the branch” and come in a form that birds can swallow whole. After ingesting the highly nutritious fruit, birds move to other regions of the forest and eventually either regurgitate or defecate the seeds, enabling new fruit tree growth.

In contrast, some species evolve to try to fool or discourage predation by other species, lead- ing the prey species to also evolve in what some ecologists refer to as an evolutionary arms race. An example of this form of coevolution involves the rough-skinned newt and the com- mon garter snake. The rough-skinned newt secretes a toxin through its skin known as tetro- dotoxin, or TTX, the same toxin found in blowfish. TTX is extremely toxic, and a single newt can secrete enough of this toxin to kill multiple humans. Newts have evolved to produce this toxin in order to discourage other organisms that might prey on them. In response, garter snakes that share the ecosystem with rough-skinned newts have also evolved to develop a resistance to TTX. Over time, newts have evolved to secrete ever more TTX, and natural selec- tion has favored the snakes that have kept up through an even greater resistance to this toxin.

Learn More: Coevolution

These links tell more about the story of the rough-skinned newt and the garter snake.

• https://news.stanford.edu/news/2008/march12/newts-031208.html • https://www.theatlantic.com/science/archive/2016/06/the-very-long-war-

between-snakes-and-newts/486311

How Biodiversity Impacts Species Interactions and Ecosystem Functioning The diversity of species within an ecosystem influences how species interact with one another. As described briefly earlier in the chapter, different species occupy different ecological niches

https://news.stanford.edu/news/2008/march12/newts-031208.html

https://www.theatlantic.com/science/archive/2016/06/the-very-long-war-between-snakes-and-newts/486311

Section 2.5 What Is Biodiversity, and Why Does It Matter?

within an ecosystem. You can think of a niche as an organism’s “place” in an ecosystem, includ- ing the kinds of food it eats and the places it lives and reproduces. Some animals, known as generalists, are more adaptive and flexible than others. Other animals, referred to as spe- cialists, have very specific niches. For example, raccoons are often cited as an example of a generalist species because they are found in so many different places and can subsist on so many different types of food sources. In contrast, koalas are only found in a limited area where they can access what is virtually their only food source, eucalyptus leaves. An organ- ism’s niche will often be an important factor in determining the ecosystem’s carrying capacity for that species. The carrying capacity is the number of individuals in a population that an ecosystem can support without degrading the ecosystem. Generally, the broader the niche, like that of the raccoon, the greater the carrying capacity.

Ecologists also classify species by whether they are native or nonnative. Native species include plants, animals, and other organisms that exist in a given location through natural processes such as natural selection and evolution. In contrast, nonnative species are those that are introduced to an area intentionally or accidentally. Some nonnative species find an ecological niche in their new habitat that is not disruptive to the native species that were there before them. However, other nonnative species can be extremely disruptive and either compete with or prey on native species. These disruptive, nonnative species are usually referred to as inva- sive species. For example, the mongoose is a small but voracious predator that was intro- duced from Southeast Asia to Hawaii, Central America, and South America to help control rat populations. However, the mongooses did not limit their hunting to rats, and they have been blamed for declines in bird, reptile, and small mammal populations in these areas.

Two other important categories of species are indicator and keystone. Indicator species can be thought of as an early warning or alarm species. Their absence or presence is an indication of a change in environmental conditions. For example, certain types of aquatic plants—like eel grass, water lily, and purple loosestrife—are known to be sensitive to water pollution. Their presence or absence is an indication of good or bad water-quality conditions. Keystone species are critical species in an ecosystem, and their absence can affect other species and even alter the entire ecosystem. Keystone species are named after the keystone in an archway, without which the whole arch collapses. An example of a keystone species is the sea otter. Sea otters feed on sea urchins, and sea urchins feed on underwater kelp forests, which provide habitat to many forms of marine life. In locations where sea otter populations have declined (due to hunting, pollution, and diseases spread from land), sea urchin populations have been able to grow. The greater number of sea urchins led to destruction of kelp forests, which in turn affected other species and the entire ecosystem. Keystone species are usually the apex predators in a particular food chain, meaning that they are at the top of food chains, with no natural predator of their own. When the population of a keystone species declines or is eliminated from an ecosystem, it can have serious ripple effects on the rest of the organisms in that food chain. This is known as a trophic cascade—recall that each link in a food chain is a different trophic level.

Section 2.5 What Is Biodiversity, and Why Does It Matter?

Why Biodiversity Is Important Biodiversity is important to human well-being and survival. As previously discussed, ecosys- tems with high rates of biodiversity are more productive; better at providing important eco- system services, including those critical to food security and water quality; and better able to withstand environmental change and disturbances like drought and pest infestations.

Biodiversity is a source of many products and services that most of us depend on directly. For example, it’s estimated that over half of all modern medicines have been derived or based on compounds found in nature. This list includes medicines like penicillin, cortisone, and pacli- taxel, which are used as antibiotics, birth control, and treatments for inflammation, cancer, and arthritis. Biodiversity is also the basis for entire tourism and recreational hunting and fishing industries. These activities generate billions of dollars in economic activity annually.

Finally, biodiversity can be said to have value to humans for its sheer existence. Individuals might not ever expect to see an elephant or orangutan in their lifetime, but they still might derive joy from simply knowing that such species exist. Environmental economists refer to this as “existence value,” and they cite as evidence the millions of dollars that individuals donate to nature conservation causes.

Ecologists and ecological economists sometimes divide those ecosystem services that directly benefit humans into different categories. These include supporting services (like photosyn- thesis and primary production), provisioning services (like seafood or lumber from forests), regulating services (such as natural water filtration by trees and forests), and cultural services (such as recreational tourism and existence value). We can clearly see that biodiversity is a form of natural capital. It provides us with services, products, recreation, and spiritual enjoy- ment—without which we cannot survive. Given biodiversity’s critical importance, Section 2.6 will review the major causes of biodiversity decline. It will also discuss steps being taken at the local, national, and international level to support and preserve biodiversity.

Dgwildlife/iStock/Getty Images Plus Sea otters are an example of a keystone species because they are vital to the proper functioning of the ecosystem they inhabit. Where sea otter populations have declined, sea urchin populations have exploded and caused further ripple effects in the ecosystem.

Eduardo Baena/iStock/Getty Images Plus

Section 2.6 Threats to Biodiversity and What Can Be Done About Them

2.6 Threats to Biodiversity and What Can Be Done About Them

Long before humans began wandering the Earth, new species of insects, birds, plants, mam- mals, and amphibians emerged while others went extinct. Many of these extinctions occurred during one of five mass extinction events that happened millions of years ago. These mass extinction events were triggered by massive volcanic eruptions, asteroid impacts with Earth, or extreme changes in climate. Since then, extinctions continued to occur naturally, but at a gradual rate that ecologists refer to as the background extinction rate. Today, as described in Chapter 1, we are in the early stages of a sixth mass extinction event. However, the primary causes of this current spike in extinction rates—far beyond background extinction rates—are due to human actions and activities.

Threats to Biodiversity The major threats to biodiversity and major causes of extinction are habitat destruction and fragmentation, introduction of invasive species, overexploitation, pollution, and climate change. The most damaging of these is habitat destruction. Deforestation, draining wetlands, and conversion of grassland and other open spaces to farms and residential developments are all examples of habitat destruction. The links between habitat destruction and biodiversity loss should be obvious. Because animals are adapted to specific ecological niches, they often cannot respond to the destruction of their habitat by simply moving some- where else. Because of this, generalist species are more likely to withstand destruction of their habi- tat, compared to specialist species.

Habitat fragmentation refers to the breaking up of large areas of habitat into smaller and smaller frag- ments. Habitat fragmentation disrupts food webs, alters reproductive activities, and can even change the microclimate of an ecosystem, all of which can lead to biodiversity decline and extinction.

Invasive species are another major cause of biodi- versity decline and extinction, for reasons described earlier. Some invasive species are introduced to a new environment by accident, while others, such as the mongoose, have been introduced with some specific purpose in mind. Either way, invasive spe- cies can outcompete or prey on native species to the point of extinction.

Humans have long hunted, fished, and trapped wild animals for food and other necessities, as well as

Sebastian Kennerknecht/Minden Pictures/SuperStock This highway cuts through habitat and ends up being a barrier for wildlife— an example of habitat fragmentation. To avoid this, some projects create “wildlife corridors” that allow animals to pass over or under roads, thereby minimizing disruption.

Section 2.6 Threats to Biodiversity and What Can Be Done About Them

collected plants and other materials to meet their survival needs. When these activities are undertaken on a scale and in a time frame that allows populations to recover and stay relatively constant, they can be considered sustainable. However, over the past 200 years and in many places around the world, these activities have started to occur on a scale that is not sustainable, resulting in what ecologists refer to as overexploitation. Perhaps the most famous example of extinction due to overexploitation is that of the passenger pigeon. These birds were once so widespread over the American Midwest that giant flocks of them would literally darken the sky as they flew overhead. It’s estimated that there were once between 3 billion and 5 billion of these birds, and in only a matter of decades, they were hunted to complete extinction for their meat. Other examples of overexploitation include overhar- vesting whales for meat, poaching elephants and rhinos for ivory, and even overharvesting ginseng root from forested regions of Appalachia for export as a medicinal plant to Asia.

Pollution and climate change are the final two major causes of biodiversity decline and extinction. In addition to eutrophication (see Section 2.4), pollution from oil spills, acid mine drainage from coal mines, and sedimentation from agriculture and land clearance for housing and commercial developments can all impact biodiversity negatively. Climate change is affecting species directly and indirectly. For example, polar bears rely on floating sea ice to help them reach their most important food source, Arctic seals. However, because of climate change, there is less sea ice for the polar bears to use, and as a result some popu- lations of this species are in decline. Elsewhere, climate change is altering habitat, disrupt- ing migration cycles, and modifying animal behavior in ways that are hindering the ability of some species to adapt and survive. Again, these changes tend to have a more serious impact on specialist species than generalist species, since the former are usually less able to adapt.

As factors like habitat destruction, overexploitation, and climate change impact biodiver- sity, ecologists use a variety of categorization systems to rank just how threatened a par- ticular species might be. A group called the International Union for Conservation of Nature (IUCN) has developed a database of at-risk species and regularly publishes what it calls the IUCN Red List of Threatened Species, which names those species at greatest risk. The IUCN Red List currently includes over 23,000 species that are considered critically endan- gered, threatened, or vulnerable. Current rates of extinction are estimated to be as much as 100 to 1,000 times higher than “normal” or background rates (see Learn More: The End of Nature?), and this is why many ecologists are worried that we are entering a period of a sixth mass extinction.

Section 2.6 Threats to Biodiversity and What Can Be Done About Them

Learn More: The End of Nature?

On May 6, 2019, the United Nations Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) released a report stating that human actions are transforming the planet and driving species to extinction at “unprecedented” rates. The 1,500-page report, written by 145 expert authors and based on a review of 15,000 scientific studies, represents the most comprehensive review ever undertaken of global threats to biodiversity and the impact this could have on human civilization.

While the IPBES report stressed that it is not “too late” to make a difference, the key takeaways from the document are sobering and staggering. First, the report estimates that as many as 1 million species of plants and animals are threatened with extinction in the coming decades, more than at any other time in human history. This includes more than 40% of amphibian species, almost one third of coral reef species, and over one third of all marine mammals. Second, human activities have now altered over 75% of the global land surface and over 66% of marine environments, transforming habitat and leaving less room for other organisms. Third, climate change and pollution are already driving species to extinction. For example, marine plastic pollution has increased 1,000% since 1980 and has reached a level that now threatens 86% of marine turtles and 44% of seabirds.

The IPBES report does not put a direct dollar value on what the extinction of 1 million species would mean for us, but we know enough about biodiversity and ecosystem services to know that human societies would be impacted negatively and severely. A loss of this many species in such a short time would have ripple effects across many economic sectors. Agriculture could be negatively impacted by the loss of pollinating insects (see Close to Home: Protecting Pollinator Biodiversity at the end of this section). Fisheries would be impacted by the loss of marine habitat and keystone species. Recreation and tourism could be devastated as formerly pristine areas are increasingly impacted by human actions. And overall, we know that a loss of biodiversity reduces ecosystem productivity and resilience, with hard-to- predict impacts on a wide range of ecosystem services critical to human well-being.

The IPBES report calls for immediate and bold action to address this biodiversity crisis. Recommended actions include investments in protected areas and conservation, stepped- up efforts to slow climate change, and global cooperation to address “transboundary” environmental problems like marine plastic pollution and the transport of invasive species.

More information on the IPBES report can be found here:

• https://www.ipbes.net/news/Media-Release-Global-Assessment • https://www.ipbes.net/news/ipbes-global-assessment-summary

-policymakers-pdf

bruno dumais/iStock/Getty Images Plus More than 40% of amphibian species are threatened with extinction.

https://www.ipbes.net/news/Media-Release-Global-Assessment

https://www.ipbes.net/news/ipbes-global-assessment-summary-policymakers-pdf

Section 2.6 Threats to Biodiversity and What Can Be Done About Them

Taking Action Recognizing the importance of biodiversity to human well-being, ecologists and other environmental scientists are advocating a number of approaches to address biodiver- sity loss and extinctions. These approaches include government action at the national and international level as well as efforts by businesses, community organizations, and individuals.

Within the United States the Endangered Species Act (ESA) has played an important role in addressing the biodiversity crisis. The ESA lists both endangered species (considered to be in imminent danger of extinction) and threatened species (those that are at risk of becoming endangered). There are currently over 1,300 ESA–listed species. The ESA restricts the direct harvest or overexploitation of these listed species, as well as activities that might impact or destroy their habitat. Well-known ESA–listed species include the grizzly bear, jag- uar, manatee, sea otter, sea lion, polar bear, blue whale, killer whale, gray wolf, California con- dor, and northern spotted owl. While the ESA has had some notable success stories, includ- ing the bald eagle, it is not without controversy. Property rights groups argue that the ESA interferes with the rights of individual landowners. Conservation groups argue that the ESA is too focused on protecting individual species rather than broader habitats and landscapes that support those species. Either way, since it was enacted in 1973, the ESA has played an important part in addressing the biodiversity crisis in the United States.

At the international level, there are a number of agreements designed to help protect biodi- versity, including the Convention on Biological Diversity and the Convention on International Trade in Endangered Species. The Convention on Biological Diversity has three interre- lated goals: conserving biodiversity, promoting the sustainable use of biodiversity, and ensur- ing that the benefits of biodiversity are shared equitably. The Convention on International Trade in Endangered Species (CITES) is more narrowly focused on prohibiting and regulat- ing international trade in endangered species. One of the most important accomplishments of CITES was the 1989 ban on international trade in ivory, which helped slow the decline in pop- ulations of African elephants. Today scientists working under the CITES structure use DNA testing and other forms of forensic science to track down and prosecute individuals involved in illegal trade in endangered species.

Besides legal and regulatory action to protect biodiversity, there are other steps being taken to address the challenge of species loss and extinction. For example, the Forest Stewardship Council (FSC) is an independent organization that certifies forest management operations as sustainable. Individual consumers and businesses purchasing lumber and other forest products (including coffee) with the FSC label are helping promote forest management prac- tices that protect biodiversity. A similar certification effort related to seafood is known as the Marine Stewardship Council. In regions of the world with high rates of biodiversity, ecotour- ism can be a way for local communities to benefit from the conservation of nature and often includes the establishment of nature/wildlife preserves and other protected areas. Lastly, there is an entire field of science focused on restoration ecology, an approach to habitat man- agement designed to reverse environmental degradation and restore ecosystems to condi- tions more favorable to biodiversity.

Bicho_raro/iStock/Getty Images Plus Ecotourism, if properly managed, can educate the public about conservation while protecting animals and environment.

Section 2.6 Threats to Biodiversity and What Can Be Done About Them

Close to Home: Protecting Pollinator Biodiversity

Honeybees often come to mind when we think of pollination, but pollinators are far more diverse than many of us realize. For example, hoverflies, plasterer bees, Mexican long- tongued bats, and monarch butterflies are all wild pollinators.

Unfortunately, many wild pollinators are threatened, and pollinator biodiversity is in decline. Industrial farming and invasive plant species have replaced native vegetation, making it difficult for wild pollinators to find food. Similarly, ecosystem destruction and fragmentation from human development have reduced the amount of food and habitat available. Pesticide use and drift from aerial spraying is another major threat to many insect pollinators.

So what can we do to reverse some of these trends and support the native pollinators where we live? First, let us meet a few wild pollinators and see if we can get a better sense of what their needs are.

Hoverflies can be seen hovering around the nectar and pollen sources that they feed on. Like many wild pollinators, they prefer to feed on the native plant species that they evolved alongside. Some hoverfly larvae also eat aphids and other pests. In other words, a good alternative to using insecticides is to plant native flowers around farms and gardens to attract those pollinators that prey on pests.

schnuddel/iStock/Getty Images Plus Carola Vahldiek/imageBROKER/SuperStock

Glenn Bartley/All Canada Photos/SuperStock MelodyanneM/iStock/Getty Images Plus Pollinators can come in all shapes and sizes. Top row, from left to right: hoverfly, plasterer bee. Bottom row, from left to right: Mexican long-tongued bat, monarch butterfly.

(continued)

Section 2.7 Planetary Boundaries

2.7 Planetary Boundaries

Human-induced environmental change is not necessarily a new thing. Ancient Maya and Roman civilizations were responsible for deforestation of large areas, and agriculture in a region known as Sumer resulted in soil degradation and the collapse of entire communities. However, the kind of human-induced environmental change and destruction we are witness- ing today are fundamentally different from those of the past in three important ways.

First, the pace of change is much greater now than ever before. Chapter 3 will show how human populations have grown slowly over thousands of years before exploding to over 7.7 billion today. Population growth and technological advances have prompted us to extract and consume far more resources per person than ever before. The net result is that environmental change is happening far faster than ever before.

Second, the scale of environmental degradation and change has gone from mostly local/ regional to global. The phrase “global environmental change” is relatively new, and it’s only in recent decades that the cumulative impact of human actions began to be felt on a global scale.

Third, the type of environmental change we are witnessing today is different from environ- mental changes of the past. Modern environmental problems are persistent; they compound one another, and more and more of them have the potential to be irreversible over time. For example, each year the chemical industry develops about 1,000 new compounds and produces

Close to Home: Protecting Pollinator Biodiversity (continued)

The plasterer bee takes its name from the smooth interior walls of its underground nests. This kind of habitat is not at all uncommon. The vast majority of pollinating bees live in the ground, hollow plant stems, and woody cavities. They tend to thrive in places that have some bare soil, shrubs, and dead wood to provide habitat. If we want to support a variety of pollinating bees, we need to make sure that they have good places to nest.

The Mexican long-tongued bat depends on plant varieties with larger flowers than most, and one of its main food sources is nectar from agave plants that are native to the southwestern United States. The Mexican long-tongued bat demonstrates that different pollinators require different flowers to thrive. If we want to encourage a variety of wild pollinators, we need to make sure that they have a variety of flowers to choose from.

Perhaps the prettiest wild pollinator is the North American monarch butterfly, which is also famous for its annual migration to overwintering sites in Mexico. These creatures need to fuel up in the late fall before their 4,800-kilometer (3,000-mile) journey south, so flowers that bloom at this time are particularly important to their survival. Like monarchs, many wild pollinators have seasonally specific nutritional needs, and they require flowers that bloom at the right time(s).

Now that you have a better sense of wild pollinator needs and the specific activities that are leading to biodiversity declines, take a moment to plan a theoretical garden for your hometown that would give local pollinators an extra boost. Are there ways you could provide a greater diversity of food sources and habitat? Are there ways that you can avoid using harmful pesticides? Most importantly, is it possible to act on your plan around your home or in your neighborhood? If you want to get serious about protecting wild pollinators, visit Pollinator Partnership at https://pollinator.org. This nonprofit has created planting guides and other online resources to help you create pollinator-friendly yards and gardens.

Section 2.7 Planetary Boundaries

over 90 million metric tons of chemicals in the form of 70,000 different compounds. Only a small fraction of these compounds are thoroughly tested or really understood before they are released to the environment.

In the past, human actions were just one of many factors shaping ecosystems and the world around us. Today they are the dominant influence on the environment—this is why some refer to the current period as the Anthropocene. To better grasp what the scope of human impact is, a group of scientists with the Stockholm Resilience Centre in Sweden developed the concept of planetary boundaries. Planetary boundaries are intended to provide a framework for develop- ing a “safe operating space” for humanity with respect to global environmental conditions.

You can think of planetary boundaries in the same way that you and your doctor might con- sider things like blood pressure, blood sugar, weight, cholesterol levels, lung function, heart rate, and other health indicators. Doctors measure and monitor these indicators to determine if a patient might be at risk of health problems or even death. Likewise, planetary boundar- ies are a collection of nine Earth-system processes with associated safe and unsafe operating spaces. These nine Earth-system processes include the following:

1. stratospheric ozone depletion 2. biodiversity loss 3. chemical pollution 4. climate change 5. ocean acidification 6. freshwater consumption 7. land use change 8. nitrogen and phosphorous flows to the biosphere and oceans 9. atmospheric aerosol pollution

Of these nine measures, the scientists with the Stockholm Resilience Centre estimate that we have already exceeded a safe operating space in three areas: biodiversity loss, climate change, and human interference with the nitrogen cycle. Other areas of concern include ocean acidi- fication, interference with the phosphorous cycle, freshwater use, and changes in land use. Returning to the analogy of the doctor, the planetary boundaries exercise tells us that we are putting the health of the planet at risk, and this could have direct consequences for our own health and well-being.

Of particular concern is the possibility that we may soon be approaching thresholds or tip- ping points with respect to some of these indicators. This could result in feedback loops that reinforce and worsen initial conditions, eventually leading to irreversible environmental change. The hope of the group involved in developing the planetary boundaries concept is that we will heed the warning signs and begin to do more to address critical environmental challenges like biodiversity loss before it is too late.

Bringing It All Together

The goal of this chapter was to provide you with a solid foundation in ecology to prepare you for some of the material presented in subsequent chapters. It is especially important that you understand how ecosystems are defined, how they function, and how the organ- isms found within them interact and interrelate with one another. This includes grasping the key concepts of energy flow through ecosystems and matter cycling within ecosystems. The Gulf of Mexico dead zone case study helped illustrate how these ecological concepts can be applied to real-world environmental challenges.

This chapter also focused on helping you develop a better understanding of what is meant by biodiversity, why it’s important, and why it’s under threat. According to the concept of planetary boundaries, biodiversity loss is one of three indicators that our actions are already pushing past safe limits.

Chapter 3 will explain the role that population growth and material consumption play in bringing about this situation. Subsequent chapters will take a closer look at specific environ- mental challenges related to things like food, water, and energy.

Additional Resources

Ecosystems

The idea of “feedback loops” can be a difficult concept to understand. These two links help illustrate what feedback loops are and how they work in nature.

• https://www.e-education.psu.edu/geog30/node/326 • TED-Ed: Feedback Loops: How Nature Gets Its Rhythms:

https://www.youtube.com/watch?v=inVZoI1AkC8&feature=youtu.be

A nice introduction to a number of ecosystem concepts can be found in this video.

• Bozeman Science: Ecosystems: https://www.youtube.com/watch?v=Ot_KmOTYfRA&feature=youtu.be

Energy Flow

This short video helps explain the basics of energy flow in ecosystems.

• http://www.bozemanscience.com/ap-es-008-energy-flow-in-ecosystems

Learn More: Planetary Boundaries

You can learn more about the planetary boundaries from the Stockholm Resilience Centre.

• https://www.stockholmresilience.org/research/planetary-boundaries/planetary- boundaries/about-the-research/the-nine-planetary-boundaries.html

• https://www.stockholmresilience.org/research/planetary-boundaries.html

https://www.e-education.psu.edu/geog30/node/326

https://www.youtube.com/watch?v=inVZoI1AkC8&feature=youtu.be

https://www.youtube.com/watch?v=Ot_KmOTYfRA&feature=youtu.be

http://www.bozemanscience.com/ap-es-008-energy-flow-in-ecosystems

https://www.stockholmresilience.org/research/planetary-boundaries/planetary-boundaries/about-the-research/the-nine-planetary-boundaries.html

https://www.stockholmresilience.org/research/planetary-boundaries.html

Bringing It All Together

This video provides a fairly detailed look into photosynthesis.

• http://www.bozemanscience.com/photosynthesis

The reintroduction of wolves into Yellowstone National Park provides an interesting case study in how food chains, food webs, and trophic levels work in nature. Reintroducing wolves set off a “trophic cascade” in Yellowstone that has resulted in a number of unex- pected but positive ecological impacts. This short video summarizes how that happened.

• Sustainable Human: How Wolves Change Rivers: https://www.youtube.com/watch?v=ysa5OBhXz-Q

Matter Cycling

A good summary of the biogeochemical (carbon, phosphorous, nitrogen) cycles can be found in this video.

• http://www.bozemanscience.com/ap-es-011-biogeochemical-cycles

Eutrophication in the Gulf

This TED Talk by marine scientist Nancy Rabalais and web summary by the Nature Conser- vancy provide an excellent overview of the Gulf of Mexico dead zone.

• https://www.youtube.com/watch?v=5zWmdHmJMd0 • Gulf of Mexico Dead Zone:

https://www.nature.org/en-us/about-us/where-we-work/priority-landscapes /gulf-of-mexico/stories-in-the-gulf-of-mexico/gulf-of-mexico-dead-zone/

Biodiversity

These links help explain the basic idea of what biodiversity is and why it is so important to our own survival and well-being.

• https://thekidshouldseethis.com/post/why-is-biodiversity-so-important-ted-ed • https://www.csiro.au/en/Research/Environment/Biodiversity/Biodiversity-book

/Chapter-1

We know that coevolution can involve two species evolving together in ways that are either mutually beneficial or that resemble an “arms race” as each tries to get the better of the other. These links show both sides of that story, featuring a bird species known as the hon- eyguide because it literally guides the people it lives with to sources of wild honey.

• https://www.youtube.com/watch?v=6ETvF9z8pc0&feature=youtu.be • https://www.audubon.org/news/meet-greater-honeyguide-bird-understands

-humans

http://www.bozemanscience.com/photosynthesis

https://www.youtube.com/watch?v=ysa5OBhXz-Q

http://www.bozemanscience.com/ap-es-011-biogeochemical-cycles

https://www.youtube.com/watch?v=5zWmdHmJMd0

https://www.nature.org/en-us/about-us/where-we-work/priority-landscapes/gulf-of-mexico/stories-in-the-gulf-of-mexico/gulf-of-mexico-dead-zone/

https://thekidshouldseethis.com/post/why-is-biodiversity-so-important-ted-ed

https://www.csiro.au/en/Research/Environment/Biodiversity/Biodiversity-book/Chapter-1

https://www.youtube.com/watch?v=6ETvF9z8pc0&feature=youtu.be

https://www.audubon.org/news/meet-greater-honeyguide-bird-understands-humans

Bringing It All Together

Threats to Biodiversity

The fact that the IPBES report described earlier estimates that over 40% of amphibians worldwide are threatened with extinction is troubling news. This is because amphibians such as frogs are key indicator species that can tell us a lot about the overall health and con- dition of our environment. The PBS Nature documentary Frogs: The Thin Green Line tells the story of this decline and what it might mean for us.

• http://www.pbs.org/wnet/nature/frogs-the-thin-green-line-introduction/4763/

A very interesting debate over how best to protect and conserve biodiversity can be summed up as “sparing vs. sharing.” The “sparing” approach generally means setting space aside for nature, while “sharing” implies managing the lands we already use in ways that also allow this land to be available to other species. A nice summary of that debate can be found here.

• https://e360.yale.edu/features/sparing-vs-sharing-the-great-debate-over-how -to-protect-nature

Key Terms atmosphere A mixture of gases, mostly nitrogen and oxygen, with smaller amounts of argon, carbon dioxide, and other trace gases, held to the Earth’s surface by gravity.

biogeochemical cycles The movement of water and chemical elements such as carbon, nitrogen, and phosphorus between living organisms and their physical environment.

biomes Ecosystems and landscapes that share similar climate and vegetation.

biosphere The zone where life exists on Earth.

carrying capacity The number of individu- als in a population that an ecosystem can support.

cellular respiration The process by which cells break down glucose and oxygen to pro- duce energy, water, and carbon dioxide.

coevolution A process whereby two dif- ferent species that interact closely together, such as a predator species and a prey species, also evolve together in a series of genetic changes.

community In ecology, a group of popula- tions that live in the same place at the same time.

consumers Organisms that rely on plants for energy, whether by eating plants directly or by eating other consumers. Also known as heterotrophs.

Convention on Biological Diversity An international agreement with three interre- lated goals: conserving biodiversity, promot- ing the sustainable use of biodiversity, and ensuring that the benefits of biodiversity are shared equitably.

Convention on International Trade in Endangered Species (CITES) An interna- tional agreement focused on prohibiting and regulating international trade in endangered species.

decomposers Organisms that break down organic material to obtain the energy and nutrients they need. Also known as saprotrophs.

ecological hierarchy A hierarchy that illus- trates the relationships between different organisms and organizes those relationships into different levels.

http://www.pbs.org/wnet/nature/frogs-the-thin-green-line-introduction/4763/

https://e360.yale.edu/features/sparing-vs-sharing-the-great-debate-over-how-to-protect-nature

Bringing It All Together

ecological niche The role and position of a species in its environment, including how it obtains food, reproduces, and finds shelter.

ecology The study of the relationships and interactions of living organisms with other living organisms and the surrounding environment.

ecosystem A community of organisms and the community’s physical environment; a collection of living (biotic) and nonliving (abiotic) entities that exist, interact, and interrelate in a particular location and time.

ecosystem diversity The variety in ecosys- tems found around the world.

Endangered Species Act (ESA) A U.S. law that provides a framework for the protection and conservation of endangered and threat- ened species and their habitats.

energy The capacity or ability to do work. In ecology, the ability of organisms to do bio- logical work (growing, eating, reproducing).

entropy The tendency for energy to move from a more useful state to a less useful state.

eutrophication A water pollution problem in which an influx of nutrients causes exces- sive plant growth, causing dissolved oxygen levels to decline sharply and thereby killing off fish and other marine life.

evolution The process whereby the genetic makeup of populations of organisms changes gradually over time.

first law of thermodynamics Also known as the law of conservation of energy; a prin- ciple which states that energy can change from one form to another but cannot be cre- ated or destroyed.

food chains Linear feeding relationships among organisms.

food web A system of many related food chains, or the many, interrelated feeding relationships within a community.

functional diversity The different ways in which organisms interact with and make use of a specific ecosystem.

generalists Species that are more adaptive and flexible and can survive in a variety of different environments and/or subsist on a variety of different foods.

genetic diversity The variety of genes and genetic material found within a population or species.

homeostasis Dynamic equilibrium; the tendency of a system to maintain relatively stable conditions over time.

hydrosphere The watery parts of the Earth: the oceans, rivers, lakes, clouds, groundwa- ter reservoirs, and glaciers that cover three quarters of the Earth’s surface.

indicator species Species whose absence or presence is an indication of a change in environmental conditions.

invasive species Nonnative species that can be disruptive and either compete with or prey on native species.

keystone species Critical species in an ecosystem; their absence can affect other species and even alter the entire ecosystem.

kinetic energy Energy in motion.

landscape In ecology, an area of interacting ecosystems.

Bringing It All Together

law of conservation of matter The prin- ciple which states that matter can neither be created nor destroyed.

limiting factor A condition or resource that limits a species’ growth.

lithosphere The solid Earth, the upper crust and uppermost mantle extending 2,500 kilometers (1,550 miles) below the surface. Also known as the geosphere.

natural selection A process whereby indi- vidual organisms within a population are better able to survive because they possess certain genetic traits. These individuals will reproduce and pass those traits on to their offspring.

negative feedback loop A condition wherein an initial change causes a system to reverse that change, essentially stabilizing the system.

nitrogen fixation A process in which cer- tain types of soil bacteria convert nonreac- tive nitrogen in the air to a usable form.

photosynthesis The process by which plants and other primary producers take sunlight, carbon dioxide, and water to make glucose and oxygen.

planetary boundaries Developed by a group of scientists at the Stockholm Resil- ience Centre, the concept that there are envi- ronmental indicators for safe human habita- tion on Earth; nine Earth-system processes that serve as measures for planetary health.

population In ecology, multiple individu- als of the same species living in a particular location.

positive feedback loop A condition wherein an initial change causes a system to keep changing further in the same direc- tion, moving the system further away from stability.

potential energy Stored energy.

primary producers Organisms that can take the building blocks of carbon dioxide and water and produce sugar (glucose) molecules with high potential energy con- tent. Also known as autotrophs or simply producers.

range of tolerance The range of conditions in which a species can survive.

second law of thermodynamics A prin- ciple which states that energy conversion will always change that energy from a more useful to a less useful state.

specialists Species that occupy very spe- cific niches and require specific conditions to survive.

species diversity The number of different species and their relative abundance in a given ecologic community.

symbiosis A close biological interaction between two organisms.

system A set of connected or interdepen- dent things that together form a more com- plex whole.

systems thinking An approach to science that considers not just the individual parts of a system but also how they interact and interrelate over time.

tipping point The point at which a series of small, gradual changes suddenly triggers a much larger or significant change.

trophic levels Hierarchal levels in a food chain. Energy is lost with each subsequent level.

Stream Morphology Investigation Manual

ENVIRONMENTAL SCIENCE

Made ADA compliant by NetCentric Technologies using the CommonLook® software

STREAM MORPHOLOGY

Overview Students will construct a physical scale model of a stream system to help understand how streams and rivers shape the solid earth (i.e., the landscape). Students will perform several experiments to determine streamflow properties under different conditions. They will apply the scientific method, testing their own scenarios regarding human impacts to river systems.

Outcomes • Design a stream table model to analyze the different

characteristics of streamflow. • Explain the effects of watersheds on the surrounding

environment in terms of the biology, water quality, and economic importance of streams.

• Identify different stream features based on their geological formation due to erosion and deposition.

• Develop an experiment to test how human actions can modify stream morphology in ways that may, in turn, impact riparian ecosystems.

Time Requirements Preparation ...................................................................... 5 minutes, then let sit overnight Activity 1: Creating a Stream Table ................................ 60 minutes Activity 2: Scientific Method: Modeling Human Impacts

on Stream Ecosystems .................................. 45 minutes

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Key Personal protective equipment (PPE)

goggles gloves apron follow link to video

photograph results and

submit

stopwatch required

warning corrosion flammable toxic environment health hazard

Key Personal protective equipment (PPE)

goggles gloves apron follow link to video

photograph results and

submit

stopwatch required

warning corrosion flammable toxic environment health hazard

Table of Contents

2 Overview 2 Outcomes 2 Time Requirements 3 Background 9 Materials 10 Safety 10 Preparation 10 Activity 1 12 Activity 2 13 Submission 13 Disposal and Cleanup 14 Lab Worksheet 18 Lab Questions

Background A watershed is an area of land that drains any form of precipitation into the earth’s water bodies (see Figure 1). The entire land area that forms this connection of atmospheric water to the water on Earth, whether it is rain flowing into a lake or snow soaking into the groundwater, is considered a watershed.

Water covers approximately 70% of the earth’s surface. However, about two-thirds of all water is impaired to some degree, with less than 1% being accessible, consumable freshwater. Keeping watersheds pristine is the leading method for providing clean drinking water to communities, and it is a high priority worldwide. However, with increased development and people flocking toward waterfront regions to live, downstream communities are becoming increas- ingly polluted every day.

From small streams to large rivers (hereafter considered “streams”), streamflow is a vital part of understanding the formation of water and landmasses within a watershed. Under- standing the flow of a stream can help to deter- mine when and how much water reaches other areas of a watershed. For example, one of the leading causes of pollution in most waterways across the United States is excessive nutrient and sediment overloading from runoff from the landmasses surrounding these waterways. Nutrients such as phosphorus and nitrogen are prevalent in fertilizers that wash off lawns and farms into surrounding sewer and water systems. This process can cause the overpro- duction of algae, which are further degraded by bacteria. These bacteria then take up the surrounding oxygen for respiration and kill multiple plants and organisms. A comprehen- sive understanding of the interaction between streams and the land as they move downstream to other areas of a watershed can help prevent pollution. One example is to build a riparian buffer—a group of plants grown along parts of a stream bank that are able to trap pollutants and absorb excessive nutrients; this lessens the effects of nutrient overloading in the streambed. (A riparian ecosystem is one that includes a stream and the life along its banks.)

Sediment, which is easily moved by bodies of water, has a negative effect on water quality. It can clog fish gills and cause suffocation, and the water quality can be impaired by becoming very cloudy because of high sediment flow. This can create problems for natural vegetation growth by obstructing light and can prevent animals

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Figure 1.

Snow

Rainfall

Precipitation

Overland flows

Underground sources

STREAM MORPHOLOGY

Background continued from visibly finding their prey. Erosion also has considerable effects on stream health. Erosion, or the moving of material (soil, rock, or sand) from the earth to another location, is caused by actions such as physical and chemical weath- ering (see Figure 2). These processes loosen rocks and other materials and can move these sediments to other locations through bodies of water. Once these particles reach their final destination, they are considered to be depos- ited. Deposition is also an important process because where the sediment particles end up can greatly impact the shape of the land and how water is distributed throughout the system (see Figure 2). Erosion and deposition can occur multiple times along the length of a stream and can vary because of extreme weather, such as flooding or high wind. Over time, these two processes can completely reshape an area,

causing the topography, or physical features, of an entire watershed to be altered. Depending on weather conditions, a streambed can be altered quite quickly. Faster moving water tends to erode more sediment than it deposits. Deposi- tion usually occurs in slower moving water. With less force acting on the sediment, it falls out of suspension and builds up on the bottom or sides of the streambed.

Sediments are deposited throughout the length of a stream as bars, generally in the middle of a channel, or as floodplains, which are more ridgelike areas of land along the edges of the stream. Bars generally consist of gravel or sand- size particles, whereas floodplains are made of more fine-grained material. Deltas (see Figure 3) and alluvial fans (see Figure 4) are sediment deposits that occur because of flowing water

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Figure 2. Figure 3.

Erosion Deposition

and are considered more permanent struc- tures because of their longevity. They are both fan-shaped accumulations of sediment that form when the stream shape changes. Deltas form in continuous, flowing water at the mouth of streams, whereas alluvial fans only form in streams that flow intermittently (when it rains or when snow melts). Alluvial fans are usually composed of larger particles and will form in canyons and valleys as water accumulates in these regions. The fan shape of both deposits is easy to spot from a distance, because they are formed due to the sand settling out on the bottom of the streams.

Streamflow Characteristics Discharge, or the amount of water that flows past a given location of a stream (per second), is a very important characteristic of stream- flow. Discharge and velocity (the speed of

the water moving in the stream) are both vital to the shaping of streambeds. Within stream ecosystems, there are microhabitats (smaller habitats making up larger habitats) that have different discharges and velocities. The type of microhabitat depends on the width of that part of the stream, the shape of the streambed, and many other physical factors. In areas that contain riffles, water quickly splashes over shallow, rocky areas, which are easily observed in sunny areas (see Figure 5). Deeper pools of slower moving water also form on the outside of the bends of the streams, as shown in Figure 5. Runs, which are deeper than riffles but have a moderate current, connect riffles and pools throughout the stream. The source of a stream

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Figure 4.

Figure 5.

PoolRiffles

STREAM MORPHOLOGY

Background continued is where it begins, while the mouth of a stream is where it discharges into a lake or an ocean.

Flow rate is very helpful for engineers and scientists who study the impacts of a stream on organisms, surrounding land, and even recreational uses such as boating and fishing. The speed of the water in specific areas helps to determine the composition of the substrate in that area of the streambed, i.e., whether the material is more clay, sand, mud, or gravel. Particle sizes of different sediments are shaped and deposited throughout various areas of a stream, depending on these factors.

Most streams have specific physical features that show periodicity or consistency in regular

intervals. Meanders can occur in a streambed because of gravity. Water erodes sediment to the outside of a stream and deposits sediment along the opposite bank, forming a natural weaving or “snaking” pattern. This pattern can form in any depth of water and along any type of terrain. Sinuosity is the measure of how curvy a stream is. This is a helpful measurement when determining the flow rates of streams because it can show how the curves affect the water velocity. In major rivers and very broad valleys, meanders can be separated from the main body of a river, leaving a U-shaped water body known as an oxbow lake (see Figure 6). These lake formations can become an entirely new ecosystem with food and shelter for some organisms, such as amphibians, to thrive in.

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Figure 6.

Oxbow Lake Formation

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Another feature important for streamflow is the difference in elevation, or the relief of a stream as it flows downstream. Streams start at a higher elevation than where they end up; this causes the discharge and velocity at the source versus that at the mouth of the stream to be quite different, depending on the meandering of the stream and the type of deposition and erosion that occurs. The gradient is another important factor of stream morphology. This is a measure of the slope of the stream over a particular distance (the relief over the total distance of the stream). For a kayaker who wants to know how fast he/she can paddle down a particular stream, knowing the difference in elevation (relief) is important over a particular area; however, knowing the slope of this partic- ular area will give the kayaker a more accurate prediction. With erosion and deposition occur- ring at different rates and at different parts of the stream, knowing the gradient is a very important part of determining streamflow for the kayaker.

Groundwater is also affected by changes in the stream shape and flow. Water infiltrates the ground in recharge zones. If streams are contin- uously flowing over these areas, the ground is able to stay saturated. Most streams are peren- nial, meaning they flow all year. However, a drought or an extreme weather event may lower the stream level. This can lower the ground- water level, which then allows the stream to only sustain flow when it rises to a level above the water table. With the small amount of available freshwater on Earth, it is vital that our ground- water sources stay pristine.

Biotic and Economic Impacts of Streams Not only are streams a major source of clean

freshwater for humans, but they are also a hotspot for diversity and life. There is great biotic variability between the different microhabitats (e.g., riffles, pools, and runs) of a stream. Riffles, in particular, have a high biodiversity because of the constant movement of water and replenish- ment of oxygen throughout. Pools usually have fewer and more hardy organisms in their slower, deeper moving waters where less oxygen is available. There are also a multitude of plant and animal species living around streams. From a stream in a backyard to the 1,500-mile-long Colorado River, streams have thousands of types of birds, insects, and plants that live near them because they are nutrient-rich with clean freshwater. Sometimes nutrient spiraling can occur in these streams. Nutrient spiraling is the periodic chemical cycling of nutrients throughout different depths of the streams. This process recycles nutrients and allows life to thrive at all depths and regions of different-size streams.

Streams can also have significant economic impacts on a region. Streams are a channel for fishing and transportation, two of the largest industries in the world. Because of all the commercial boating operations that occur world- wide in these channels, it is vital to understand the formation and flow patterns of streams so that they are clear and navigable. Fishing for human consumption is another large, worldwide industry that depends on stream health; keeping streams pristine and understanding how they form are of utmost importance in sustaining this top food industry. Recreational activities such as kayaking, sportfishing, and boating all shape areas where streams and rivers are prevalent as well.

STREAM MORPHOLOGY

Background continued All acts that happen on land affect the water quality downstream. Through creating a model stream table in this lab, one can predict large, system-wide effects. Many land features and physical parts of a streambed can affect the flow of water within a watershed. Houses along a streambed or numerous large rocks can cause the streamflow to change directions. If any of these factors cause erosion or deposition in an area of the stream, microhabitats can be created. These factors can affect the stream on a larger scale, creating changes in flow speeds and widths of the streambeds.

The Importance of Scaling and the Use of the Scientific Method When a stream table model is created, a large- scale depiction of a streambed is being reduced to a smaller scale so that the effects of different stream properties on the surrounding environ- ment can be demonstrated. While the stream table made in this lab is not a to-size stream and landscape, the same processes can be more easily observed at a scaled-down size. Scientists frequently create models to simplify complex processes for easier understanding. For example, to physically observe something that is too big, such as the distance between each planet in the solar system, the spatial distance can be scaled to create a solar system model. By changing the distance between each planet from kilometers to centimeters, this large system is now more feasibly observed. Similarly, the stream model allows us to physically view different scenarios of a streambed and analyze different stream properties. Mathematical equations are also used frequently to observe

data to predict future conditions, such as in meteorological models. Ultimately, models can be very important tools for predicting future events and analyzing processes that occur in a system.

When one creates a model, many different outcomes for the same type of setup can be possible. In this case, multiple variations of similar-size streambeds will be designed to evaluate different stream features and their impacts on the surrounding ecosystem. When performing any type of scientific evalua- tion, the scientific method is very useful in obtaining accurate results. This method involves performing experiments and recording observa- tions to answer a question of interest.

Although the exact step names and sequences sometimes vary a bit from source to source, in general, the scientific method begins with a scientist making observations about some phenomenon and then asking a question. Next, a scientist proposes a hypothesis—a “best guess” based upon available information as to what the answer to the question will be. The scientist then designs an experiment to test the hypothesis. Based on the experimental results, the scientist then either accepts the hypothesis (if it matches what happened) or rejects it (if it doesn’t). A rejected hypothesis is not a failure; it is helpful information that can point the way to a new hypothesis and experiment. Finally, the scientist communicates the findings to the world through presenting at a peer-reviewed academic conference and/or publishing in a scholarly journal like Science or Nature, for example.

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When creating stream table models, we are trying to understand how different factors can affect streamflow. A few very important steps from the scientific method are required. The first is forming a testable hypothesis, or an educated prediction, of what you expect to observe based on what you have learned about stream morphology thus far. In Activity 1, the steps are already listed, so the main goal is to compare the two differences in stream reliefs. However, in Activity 2, the goal is to alter a different vari- able and predict what will happen to several stream features in this new situation. In general, when recording these observations to test a hypothesis, it is important to repeat the tests. To obtain valid results, you need to have similar results over multiple attempts to ensure consis- tency in the findings and to show that what you are discovering is not by chance but is instead replicated each time the experiment is run. While multiple trials are not required in this lab experi- ment, if you feel particularly less than confident with your results from doing only one trial run in Activity 1 or 2, feel free to do multiple trials to test for validity.

Materials Needed but not supplied: • Tray or cookie sheet (or something similar) • 2–3 lb bag of play sand (not construction sand

or any other type of sand or soil) or, if that is unavailable, substitute with 1 lb bag (or more) of plain cornmeal (not self-rising)

• Single-use cup that can have a hole poked in it (e.g., plastic yogurt cup, foam cup)

• Small piece of foam (such as from a foam cup), about the size of a grain of rice

• Cup, such as a glass, mug, or plastic cup • Paper clip, skewer, or thumbtack (to poke a

hole in the single-use cup) • 2 books, one approximately twice as thick as

the other • Ruler (There is a ruler in the Equipment Kit if

you have already received it, or you can print one at a website such as printable-ruler.net.)

• Tap water • 2 Plastic bags (to cover the books or objects

you don’t want to get wet) • Stopwatch (or cell phone with a timer) • Digital camera or mobile device capable of

taking photos • Piece of string • Marker

https://printable-ruler.net

STREAM MORPHOLOGY

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Safety Wear your safety goggles, gloves, and lab apron for the dura- tion of this investigation.

Read all the instructions for these laboratory activities before beginning. Follow the instruc- tions closely, and observe established laboratory safety practices, including the use of appropriate personal protective equipment (PPE).

Do not eat, drink, or chew gum while performing these activities. Wash your hands with soap and water before and after performing the activities. Clean the work area with soap and water after completing the investigation. Keep pets and chil- dren away from lab materials and equipment.

Preparation

Note: This investigation is best performed outdoors or in an area in which it is easy to clean up wet sand/cornmeal and water. Do not dump any of the sand/cornmeal and water mixture down the sink, because it can cause clogging.

1. Read through the activities. 2. Obtain all materials. 3. Pour the sand or cornmeal in one, even layer

on the tray or cookie sheet. 4. Pour water slowly over the sand/cornmeal

until it is completely saturated. Pour off any excess water outside.

5. With your hands, rub the sand/cornmeal so it is flat, and let it dry overnight in the tray/ cookie sheet.

6. Using the paper clip, skewer, or thumbtack, poke a hole in the side of the single-use cup, 1 cm up from the bottom of the cup.

ACTIVITY 1

ACTIVITY

A Creating a Stream Table In this activity, you will be measuring different factors (see Step 5) for two different stream models: one where the streambed is tilted at a steeper angle and another where the streambed is tilted at a shallower one. Propose four sepa- rate hypotheses for which of the two streambed angles (steeper or shallower) will have the highest values for sinuosity, velocity, relief, and gradient. Briefly state why you feel that way. Complete this information in the “Hypotheses” section of the Lab Worksheet. 1. Bring the tray outside. Place the thicker book

in a plastic bag. Place the tray on one end of the book so it is tilted (see Figure 7).

2. Fill the cup without a hole in it with tap water and slowly pour the water into the single-use cup. Ensure that the single-use cup is right above the higher end of the tray. Note: Store extra tap water on-site if more water is needed to form a stream.

3. Let the water trickle out of the hole in the single-use cup down the sand/cornmeal. Observe how the water forms a “stream” in the table. Stop pouring after a small streamflow has formed down the table.

Poking a Hole in a Cup to Create a Stream https://players.brightcove. net/17907428001/HJ2y9UNi_default/ index.html?videoId=5973740372001

Figure 7. Tray Thicker book

https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=5973740372001

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iii. Now, divide the curvy distance by the straight distance. Note: If there is no curvy distance (if the stream forms straight down the table), then the sinuosity is 1.

How to Measure the Sinuosity of a Stream https://players.brightcove. net/17907428001/HJ2y9UNi_default/ index.html?videoId=5973736251001

b. Velocity = distance traveled (cm)/time to travel (s) (recorded in cm/s)

Obtain the small piece of foam (about the size of a grain of rice). Hold the single-use cup over the raised edge of the stream table, allow water to flow out of the hole, and drop the piece of foam into the top of the stream. Time how long it takes (in seconds) for the piece of foam to float downstream. Divide the curvy distance by this time.

How to Measure the Velocity of a Stream https://players.brightcove. net/17907428001/HJ2y9UNi_default/ index.html?videoId=5973739032001

c. Relief = highest elevation (cm) − lowest elevation (cm) (recorded in cm)

Measure the elevation change from the beginning to the end of the stream. Use the ruler to measure the highest point of the incline to the ground for the highest elevation and measure the bottom part of the tray to the ground for the lowest elevation.

4. On a blank sheet of paper, carefully sketch what the formed stream looks

like. Clearly label where erosion and deposition have occurred along the streambed. Take a photograph of your completed drawing and another photograph of your actual stream table. In the stream table photograph, include a strip of paper with your name and the date written on it. You will be uploading both photographs to your lab report.

5. Use the instructions below to calculate the values for the different physical stream features in the “Calculations” section of the Lab Worksheet. Record these values in Data Table 1 of the “Observations/Data Tables” section of the Lab Worksheet.

a. Sinuosity = curvy distance (cm)/straight distance (cm) (no units)

i. Use a piece of string to measure the distance from the mouth to the source of the stream along the curve (curvy distance). Once you have used the string to trace the stream, hold each end of the string, straighten it, lay it flat, and mark where the two ends of the stream were. Use a ruler to measure this distance between the marks (the curvy distance).

ii. Use a ruler to measure the distance straight down the stream from the mouth to the source of the stream (no curve— straight distance).

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https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=5973736251001

https://players.brightcove.net/17907428001/HJ2y9UNi_default/index.html?videoId=5973739032001

Note: In Activity 1, the heights of the source of the streams were altered to observe how streamflow and streambed formation were affected. In Activity 2, use your streamflow knowledge to design an experiment by altering a different characteristic. You will record the same calculations for your new experimental setup.

ACTIVITY

ACTIVITY 1 continued How to Measure the Relief of a Stream https://players.brightcove. net/17907428001/HJ2y9UNi_default/ index.html?videoId=5973740399001

d. Gradient = relief (cm)/total distance (cm) (rise/run) (no units)

Measure the slope of the stream; divide the relief by the total distance (calculated in Steps c and a). Note: If the stream is curvy, this distance is the curvy distance; if it is not, then this distance is the straight distance.

How to Measure the Gradient of a Stream https://players.brightcove. net/17907428001/HJ2y9UNi_default/ index.html?videoId=5973742678001

6. Gently pour the excess water from the stream table into the grass, and flatten the sand/ cornmeal out where the stream formed, making a uniform layer.

7. Repeat Steps 1–6 with the thinner book to obtain a more gradual stream formation.

8. While not required, if you feel particularly less than confident with your results from doing only one trial run, feel free to do multiple trials to test for validity.

ACTIVITY 2

A Scientific Method: Modeling Human Impacts on Stream Ecosystems

1. Design a procedure similar to Activity 1. Choose one height to test the trials and change a different variable to analyze the same calculations for stream movement and formation throughout the streambed. Choose a variable to change that models how humans might modify a stream channel for good or for ill. Activities such as pre-digging a stream, adding a dam or other features along the streambed, or adding plants along these areas are all common factors that can be altered within a streambed. Feel free to implement additional materials from your surroundings, such as using a rock to represent a dam, for example.

2. Hypothesize whether each of the four calculations (sinuosity, velocity, relief, and gradient) will increase, decrease, or stay the same, and include your reasoning in your choices. Record this in the “Hypotheses” section in your Lab Worksheet.

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3. Test your new experimental design by using the same procedure as in

Activity 1. On a blank sheet of paper, carefully sketch what the formed stream looks like. Clearly label where erosion and deposition have occurred along the streambed. Take a photograph of your completed drawing and another photograph of your actual stream table. In the stream table photograph, include a strip of paper with your name and the date written on it. You will be uploading both photographs to your lab report.

4. Calculate the values of the four different stream features in the “Calculations” section of the Lab Worksheet. Record your findings in Data Table 2 of the “Observations/Data Tables” section of the Lab Worksheet.

5. While not required, if you feel particularly less than confident with your results from doing only one trial run, feel free to do multiple trials to test for validity.

Submission Using the Lab Report Template provided, submit your completed report to Waypoint for grading. It is not necessary to turn in the Lab Worksheet.

Disposal and Cleanup 1. Dispose of the sand/cornmeal mixture either

in the environment or in the household trash. Dispose of any other materials in the household trash, or clean them for reuse.

2. Sanitize the work space, and wash your hands thoroughly. The single use cup may be recyclable.

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ACTIVITY

Lab Worksheet

Hypotheses Activity 1.

Sinuosity hypothesis:

Velocity hypothesis:

Relief hypothesis:

Gradient hypothesis:

Activity 2.

Sinuosity hypothesis:

Velocity hypothesis:

Relief hypothesis:

Gradient hypothesis:

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Observations/Data Tables

Data Table 1.

Trial Sinuosity Velocity(cm/s) Relief (cm) Gradient

Thicker Book

Thinner Book

Data Table 2.

Variable changed: _______________________________________________________

Book thickness used: ____________________________________________________

Trial Sinuosity Velocity(cm/s) Relief (cm) Gradient

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ACTIVITY

Lab Worksheet continued

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Calculations

Activity 1. Sinuosity: Curvy distance (cm)/Straight distance (cm) = Sinuosity (no units) ___________ / ____________ = Both the curvy and straight distances are measurements taken from the stream formation in the stream table. Please refer to Activity 1 for more details.

Velocity: Distance traveled (cm)/Time it takes to travel (s) = Velocity (cm/s) ___________ / ____________ = The distance it takes a small piece of paper to travel downstream divided by how long it takes to get downstream is the velocity. Refer to Activity 1 for more details.

Relief: Highest elevation (cm) – Lowest elevation (cm) = Relief (cm) ___________ – ____________ = By subtracting the highest elevation of the stream and the lowest elevation of the stream from each other, the relief can be calculated. Please refer to Activity 1 for more details.

Gradient: Relief (cm)/Total distance (cm) = Gradient (no units) ___________ / ____________ = By dividing the relief by the total distance of the stream, the gradient can be calculated. Please refer to Activity 1 for more details.

Activity 2. Sinuosity: Curvy distance (cm)/Straight distance (cm) = Sinuosity (no units) ___________ / ____________ = Both the curvy and straight distances are measurements taken from the stream formation in the stream table. Please refer to Activity 1 for more details.

Gradient: Relief (cm)/Total distance (cm) = Gradient (no units) ___________ / ____________ = Divide the relief by the total distance of the stream to calculate the gradient. Please refer to Activity 1 for more details.

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NOTES

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ENVIRONMENTAL SCIENCE Stream Morphology Investigation Manual

www.carolina.com/distancelearning 866.332.4478

http://www.carolina.com/distancelearning

http://www.carolina.com

CHAP 1 SCIENCE
CHAP 2 SCIENCE
LabtreamMorphology_V2.3_ADA (1)

Stream Morphology

Table of Contents
Overview
Outcomes
Time Requirements
Key
Background

Streamflow Characteristics
Biotic and Economic Impacts of Streams
The Importance of Scaling and the Use of the Scientific Method

Materials

Needed but not supplied:

Safety
Preparation
ACTIVITY 1

A Creating a Stream Table

ACTIVITY 2

A Scientific Method: Modeling Human Impacts on Stream Ecosystems

Submission
Disposal and Cleanup
Lab Worksheet

Hypotheses

Activity 1.
Activity 2.

Observations/Data Tables
Calculations

Activity 1.

NOTES