LIMITING FACTORS AND PHYSICAL ENVIRONMENTAL
FACTORS
ARIZONA STATE UNIVERSITY
ABS 370 - ECOLOGY
SPRING 2024
All organisms large and small, plants and animals including humans, depend on the
environment of their habitat. They grow and develop in a suitable environment. A healthy
environment for the development of some organisms follows the following conditions: a
place to grow and develop, fresh and sufficient air, water for nutrient transport and food
formation, mineral salts for body building, and energy for life processes.
In this world, there are two habitats: terrestrial habitats and aquatic habitats. What we
know is that because the conditions are different, the number and quality of inhabitants are
also different. The environment is a complex of factors and the atmosphere in a place is the
result of the cooperation between these factors.
Broadly speaking, these factors are divided into two namely: biotic - abiotic factors but
in detail these factors are divided into 7 parts namely: soil, water, temperature, light,
atmosphere, fire, and biotic.
Although the environment is a complex system and plays a huge role in life, life is not
This is partly because many life forms are able to modify the environment to make it suitable
for them, or the organisms try to adapt to the environment in some way.
The environment in a place is dynamic, usually the further away from the tropics (closer
to the poles) the greater the dynamics of the environment. To overcome the unfavorable
environment in plants, among others, there are several ways: adaptation, modification,
mutation, and evolution. Finally, all these processes cause a specific relationship so that it is
often found typical organisms in a particular environment, which is then called Ecotype. So
the environment and organisms have a reciprocal relationship.
A.
PRINCIPLES OF ENVIRONMENTAL FACTORS
1.
The limiting factor principle is better known as Leibig's Minimum Law: Organisms will be
inhibited in growth if one of the factors of their life needs is available in a minimum state. If
this factor is added, growth will be encouraged. In addition to the minimum limit, it turns out
that there is also a maximum limit and there is also an optimum.
On this basis, VE Shelrord (1913) stated the "law of tolerance".
a.
Organisms can have a wide tolerance range for one factor and a narrow one for another.
b.
Organisms with a wide tolerance range for all factors tend to have a wide distribution.
c.
If the optimum situation for one type of factor is not reached, then the tolerance limit for
other factors may be narrowed.
d.
A complex set of factors can be more important than any particular optimum physical
factor.
e.
The reproductive period is critical and has a narrow tolerance for all factors.
2.
Holocoenotic Environmental Principles
Environmental factors do not stand alone, but are related. It is impossible to change one
factor without affecting the others. Holocoenotic according to Karl Friedrich (Germany)
"There is no wall of separation between environmental factors and organisms (groups of
organisms). The ecosystem reacts as a unity and whole.
B.
LEIBIG'S MINIMUM LAW
To survive under certain circumstances organisms must obtain the essential elements
needed for growth and reproduction. These basic requirements vary depending on species and
circumstances. In a steady state the essential elements available in a near minimum state tend
to be limiting factors.
Leibig was a pioneer in terms of studying the influence of various factors on plant growth.
According to him, agricultural yields are often influenced not only by the large amounts of
necessary nutrients such as carbon dioxide and water that are generally abundant in the
environment, but by elements or compounds such as boron necessary in small quantities,
whose presence in nature is very few/sparse. Therefore, Leibig's Law states: "Plant growth
depends on compounds that are in a minimum state ".
Other researchers have extended this statement to include other factors such as temperature.
For Leibig's law to be useful, it must be supplemented:
"When the steady state, that is, energy and matter are balanced between input and output".
For example: In a lake, CO2 levels are the limiting factor, so productivity is in balance with
available CO2 levels when light, nitrogen, and water are sufficiently available. If in a place
there is a hurricane, the CO2 level will change followed by other substances, so in this
situation productivity does not only depend on CO2 levels but other elements whose balance
changes.
Cultural eutrophication will create an unstable situation that results in isolation of
population development. For example, a bloom of one species of algae then dies off followed
by a bloom of another species.
In this situation, the limiting factor is uncertain because the levels of P, N2, CO2, in the
environment are always changing. Another important consideration is that the necessary
substances are not available.
If Ca is scarce and strontium is plentiful, Molussca can replace the necessary Ca with Sr
Plants growing in the shade require less Zn than those growing in the light.
C.
LAW OF TOLERANCE SHELFORD
The existence and success of an organism depends on the completeness of its complex
circumstances. Failure or extinction of an organism can be controlled by a qualitative or
quantitative deficiency or excess of one of the factors close to the organism's tolerance limit.
A limiting factor actually involves a lack or excess of something such as temperature, light
and pH that is too low or too high can be a limiting factor.
Organisms have ecological maximum and minimum limits, i.e. they have a tolerance
range and this is Shelford's concept of the law of tolerance.
Some additional principles to Shelford's law of tolerance:
1.
Organisms can have wide tolerance for one factor and narrow tolerance for another.
2.
Organisms with a wide tolerance range for all their dispersal factors.
3.
Non-optimal conditions for one factor can affect tolerance to other factors. For
example, when N2 levels are low, plants will be more sensitive to drought.
4.
Many organisms in nature live in non-optimal conditions and are always influenced by
several factors at once.
5.
For example, gtropical orchids will grow better in direct light as long as the temperature
remains cool. In nature orchids Tropical plants grow in the shade because they cannot
tolerate the heat effects of direct light. In many cases, interactions between populations Growth
Activity
Stegothernal
(Oligothernal)
Eurithernal
Stenothernal
(Polythernal)
opt.
opt.
opt.
°C (°F)
(competition, parasites, predators) prevent organisms from living in optimum conditions.
6.
Generally, the reproductive period (embryos, sprouts, larvae) is sensitive to minimum
physical factors.
7.
To express the degree of tolerance, the terms: steno for narrow and euri for wide are often
used.
Compensation Factors and Ecotypes:
Organisms are not only slaves to the physical environment but can also adapt and change
the physical environment to reduce the effects of barriers to temperature, light, water and so
on. Such a state of compensation is especially effective at the community level although it
also occurs at the species level.
Widely distributed species almost always develop populations with local adaptations
called ecotypes e.g. arctic foxes have small earlobes while desert foxes have large and long
ears.
D.
A COMPOSITE CONCEPT OF LIMITING FACTORS
The existence or success of an organism or group of organisms depends on complex
circumstances. Conditions that approach or exceed tolerance limits are called boundary
conditions or limiting factors.
Organisms in nature are controlled by:
a.
Essential elements and compounds that are in a minimum state.
b.
Critical physical factors.
c.
The tolerance limit of the organism.
If the organism has a wide tolerance limit for a factor that is relatively constant and
present in large quantities then the factor is not a limiting factor. On the other hand, if the
organism has a narrow tolerance limit for a factor that is always changing then the factor may
be a limiting factor.
For example, O2 levels are large and constant in the air, so O2 is not a limiting factor for
terrestrial organisms, but in aquatic ecosystems O2 levels change frequently and in small
concentrations, oxygen is a limiting factor for aquatic organisms.
E.
CONDITION OF EXISTENCE AS A REGULATING FACTOR
Light, temperature and water are ecologically important environmental factors for land
while light, temperature and salinity are the top three factors for the ocean.
All natural physical factors are not only limiting factors in an adverse sense but also
regulating factors in a favorable sense so that the community is always in a homeostatic state.
In nature, organisms not only adapt to the physical environment in terms of tolerance,
but also utilize natural periodicity to regulate activities and program life. For example, in
temperate climates the activities of organisms are adjusted to the length of the day
(photoperiod).
Photoperiod will affect the physiology of organisms, including: growth, flowering (long
day plant and short day plant), molting, migration, breeding (insects) and so on.
Thisphotoperiod will befollowed by biologicalclock of the organism. Therefore, planting
plants originating from temperate climates must pay attention to this photoperiod. Timing and
an organism's activities can be changed through manipulation Trout, which normally develop
in the fall and hatch in the summer . When the length of daylight is artificially increased in
spring and decreased in summer to stimulate the fall state.
In insect groups, the production of hormones to stimulate egg laying is also influenced by
photoperiod.
Seeds of desert plants contain germination inhibitors that are washed away only when
rainfall is greater than 1 cm. Seeds like these will sprout immediately when given artificial
rain. Because of this anti-germination substance, plants in the desert only germinate when
there is sufficient rainfall.
F.
A BRIEF OVERVIEW OF PHYSICAL FACTORS AS LIMITING FACTORS
The concept of limiting factors is not only a physical factor but also an interaction that is
important to control the distribution and size of the population.
1.
Temperature
Organisms can live at temperatures between -200o C (spores and seeds) and 100o C
(bacteria, hot water algae), but most can live in a narrower temperature range.
Generally the upper limit is more critical than the lower limit. Temperature variation is
less in aquatic ecosystems therefore generally aquatic organisms have a narrower tolerance
range than equivalent terrestrial organisms, e.g. aquatic and terrestrial algae, aquatic and
terrestrial invertebrates.
Temperature variability is ecologically important because temperature fluctuations
between 10-200 C with an average of 150 C, do not always have the same effect on organisms
as a constant temperature of 150 C.
It turns out that organisms that often get temperature changes in nature, for example in
temperate climates, the tendency to spread is inhibited when given a constant temperature. In
the experiment it turned out that grasshopper eggs develop faster if the temperature is made
up and down compared to a constant temperature.
2.
Light Radiation
Organisms are on the horns of the light dilemma. Direct light will kill protoplasm but in
addition light is a source of energy for life, without light there would be no life. Therefore,
many structures and the distinctive traits possessed by the organism in relation to the way it
solves this light problem.
Light is both a vital and limiting factor for organisms. In terms of ecology, the quality of
light (wavelength, color) and the intensity of light (length of irradiation) are important.
3.
Water
Water is a basic need for organisms as a building block for protoplasm (protoplasm is
80% water), this is in terms of organism (cell) physiology. In terms of ecology, water is a
major limiting factor for terrestrial environments or water with high salinity that can cause
organisms to lose water (osmosis).
How many principle factors must be considered about water is:
a.
Rainfall
35 cm of rainfall throughout the year will have a different effect on organisms than 70 cm of
rainfall in half a year. This is because if the rainfall is only half a year even though the
average is the same, the organisms will have to adapt to half a year of dry season.
b.
Humidity
Humidity is the amount of water vapor present in the air. Absolute humidity is the ratio of the
weight of water vapor in the air by weight. Relative humidity is the percent ratio of water
vapor in the air with a certain pressure.
Some things related to humidity are:
-
Humidity can affect the temperature effect of organisms
-
Humidity fluctuates horizontally (high humidity at night and low humidity during the
day)
-
Humidity also fluctuates vertically
-
Humidity, temperature, and light play a huge role in regulating the activities of
organisms and are often limiting factors to the spread of organisms.
c.
Evaporation
Evaporation can dehydrate organisms and therefore organisms adjust their activities
according to this evaporation factor, i.e. animals are active in sheltered areas or at night. 97-
99% of water taken up by plants is lost through transpiration, expressed in grams of dry
matter produced per 1000 grams of water transpired. Most agricultural crops have high
transpiration efficiency but low productivity. Dew can be A significant contribution to areas
with low rainfall such as deserts.
4.
Temperature and Humidity Act Together
In ecosystems, environmental factors do not work individually but work together.
Temperature and humidity have a strong influence on the terrestrial environment. The
limiting effect of temperature increases when humidity is in an extreme state, namely high or
low. The interaction between temperature and humidity is like the interaction of other factors,
which depends on the relative and absolute value of each factor. The effect of humidity will
be more intense if the temperature is extreme.
For example, boll weevils can tolerate high temperatures if the humidity is not extreme.
In terms of humidity and temperature, there are two basic types of climate:
-
A marine climate characterized by less extreme fluctuations in temperature and
humidity due to the moderating effects of ocean water bodies.
-
An inland climate characterized by extremes of temperature and humidity.
-
5.
Atmospheric gases
Air CO2 content is 0.003% and O2 is 21%. In the experiment, it was found that reducing
O2 levels by 5% can increase the photosynthesis rate in beans by up to 50% but in maize and
sugarcane the decrease in oxygen levels did not show a significant effect on photosynthesis.
In soil, O2 can be a limiting factor for aerobic organisms and CO2 levels will increase deeper
in the soil.
The aquatic environment is different from the terrestrial environment because the levels
of O2, CO2, and other gases dissolved in water that can be obtained by organisms vary
greatly from time to time and from place to place because the solubility of gases in water is
influenced by temperature, pressure, and salt content. For example, O2 is a limiting factor for
waters polluted with organic substances. High temperatures and salt levels can reduce the
solubility of O2. the source of water oxygen is the result of photosynthesis and diffusion from
the air (enlarged by water movement).
CO2 in water also varies but CO2 is a gas that dissolves easily in water. The pH of water
is closely related to CO2 levels in water respiration of aquatic organisms and is often an
important limiting factor for aquatic organisms because it can affect breathing and the work
of enzymes.
6.
Biogenic salts: macro and micronutrients
Biogenic salts are salts dissolved in water that are vital to organisms. Examples are
nitrogen and phosphorus salts. Co salts are important for Mollusca and vertebrates, Mg salts
are important for plant chlorophyll.
Macronutrients include :C, H, O, N, S, P, K, Ca, Mg Micronutrients :Fe, Mn, Cu, Zn,
Si, Mo, Co, Cl.
In terms of its function in plants micronutrients can be divided into :
-
For photosynthesis: Mn, Fe, Cl, Zn, V
-
For nitrogen metaboleism: Mo, Co, Fe
-
For metabolism of other substances: Mn, B, Co, Cu, Si
Many elements that are essential for plants are also essential for animals, such as
iodine. The dividing line between micro- and macronutrients is not sharp and does not have
to be the same for all organisms. Na and Cl are needed by many animal groups, but only a
few are needed by plants. In terms of function, metal elements often act as metallo-activators,
for example Co for vitamin B12.
7.
Current and Pressure
The atmospheric and hydrospheric media in which organisms live are almost never
completely still. The presence of currents will serve as a limiting factor. For example,
differences in river and lake organisms are often caused by the presence of strong currents in
rivers. River plants and animals have adapted to currents, both morphologically and
physiologically (plants and animals have a tolerance limit to currents). In terrestrial
ecosystems wind can also be a limiting factor because Large winds will increase evaporation.
Therefore, in windy conditions insects and birds will hide in the shade to avoid the large
evaporation.
Barometric pressure has little effect on the life of terrestrial organisms although
barometric pressure can affect the climate, and this climate can affect terrestrial organisms.
This situation is different with aquatic organisms. Hirostatic pressure is a large pressure, so it
can affect the life of aquatic organisms. For every 10 m drop in water depth, the pressure will
increase by 1 atm. The destruction of objects due to large water pressure is called implosion.
8.
Land
The area where organisms live is called the biosphere which includes the atmosphere,
hydrosphere, and pedosphere (soil). Soil comes from the earth's crust layer that is weathered
by living organisms so it can be said that soil is not only an environmental factor for
organisms but also the work of organisms.
The description of soil layers (soil horizons) from the surface downwards is called a soil
profile.
-
Top layer (layer A, top soil, horizon A)
This layer contains plant and animal bodies that have been broken down into smaller pieces
by a process called humification. In mature soils this layer consists of a clear layer. Based on
the degree of humification layer A can be divided into : (from top to bottom)
-
Litter layer A-O (representing detritus component)
-
Humus layer A-1
-
Washed layer A-2 (light color)
-
B layer (B horizon)
Consists of mineral soil, where organic compounds have been converted by decomposers
into inorganic compounds through mineralization processes and then mixed with fine parent
material. The soluble material in layer b is often derived from the layer.
-
C layer (C horizon layer)
It is the parent layer that has not undergone much change. The parent material after rupture
can move because :
⮚
Gravity (colluvial deposit)
⮚
Water (alluvial deposit)
⮚
Glacier (glacial deposit)
⮚
Angina (colian deposit)
Soil profiles and relative thicknesses are generally typical for an area with a particular
climate. For example, grassland soils humify quickly, but mineralize slowly. Because new
residue is added every year (short grass life), the humus layer will be thick. In forests, the
decomposition of residues is slow, but mineralization is fast, so the humus layer is thin, only
1/11 of the grassland humus layer. Therefore, with sufficient rainfall, grasslands can become
world-weary.
Topography also greatly affects the soil of a particular climatic region. Hilly soils or
misuse of the soil by humans will result in thin A and b layers, due to erosion. On flat soils,
excessive water will wash elements into deeper horizons.
9.
Fire as a Limiting Factor
Fire is an important climatic factor for forests and grasslands in temperate and tropical
climates in the dry season because ecosystems adapt to fire as well as to temperature and
water. Generally, humans intervene to reduce the influence of fire on ecosystems, even
though nature has dealt with fire factors in areas that have not been touched by humans, in
terms of fire as an ecological factor can be divided into :
Crown Fire
This type of fire will destroy all vegetation in the ecosystem, is a limiting factor for all
organisms, takes a long time to recover because everything is destroyed.
Surface Fire
Favorable for organisms with a high tolerance to fire is only a limiting factor for some
organisms.
Surface fires can :
⮚
Reduces the work of bacteria in accelerating the decay process
⮚
Helps break down the hard bark of fruits, such as the pine group, thus aiding forest
rejuvenation.
Burning of non-forest woody debris can result in fires that are close to crown fires as
a result of which the soil becomes difficult to cultivate because the temperature during the
fire is very high. The result of burning an area can result in only plants with a high tolerance
to fire being able to re-germinate as a result of which only certain vegetation can grow. Such
vegetation is called fire climax or pyroclimax.
Microenvironment
Regional differences in temperature, humidity and other factors are important but vertical
differences are also important. Because microenvironments as opposed to
macroenvironments over the past decade have also begun to be developed. Organisms that
occupy the same general habitat (macro-environmentally) can actually be in different
circumstances micro-environmentally. Other frequently used but more limited terms are
macroclimate and bioclimate. The term microenvironment is of relative magnitude, for
example, it can be the environment around pine trees or around crustose moss but it can also
be the slope of a valley.
Differences in microclimate can be created by differences in topography, for example,
south-facing slopes receive more light than north-facing slopes. As a result, the microclimate
of south-facing slopes is completely different from that of north-facing slopes.
Differences in temperature, humidity, evapotranspiration and other factors can result in
communities that are completely different from neighboring slopes in the same ravine.
G.
ECOLOGICAL INDICATORS
Since an environmental factor often determines the organisms that will be found in an
area, we can in turn determine the state of the physical environment from the organisms
found in an area. These are called ecological indicators (biological indicators).
In the US, certain plants are often used as indicators of water or soil conditions. Some
things that need to be considered when we use biological indicators are :
-
Generally, steno organisms are better indicators than euri organisms. These indicator plants
are often not the most abundant organisms in a community.
-
Large species are generally a better indicator than small species, as species with a large
Members of large organisms that have a large biomass are generally more stable. Also, because of the
turn over rate, small organisms that are alive today may be dead tomorrow. Therefore, no algae
species are used as ecological indicators.
-
Before specifying a species or class of organism as an indicator, there must be field and, if
possible, laboratory evidence that proves that the life requirements of the organism species
are limited.
-
Many relationships between species, populations or communities are often better indicators
than individual species. This is because they better represent an integrated state.
For example, a plant can be used as an indicator of uranium, if the plant is deep-rooted
such as Tusam and Juniperus. If Tusam and Juniperus grow in areas containing uranium, the
parts on the ground will contain a lot of uranium. If the above-ground parts (leaves, twigs) are
collected and analyzed for ash the uranium content can reach 2 ppm, and this indicates a large
soil uranium content. Because selenium is often associated with uranium, plants that are
indicators for selenium such as Astragalus can also be used as indicators for uranium.
FRESHWATER ECOLOGY:
A.
FRESHWATER ECOSYSTEM
Freshwater ecosystems are aquatic ecosystems, characterized by freshwater
ecosystems:
•
The salt/salinity level is very low, even lower than the salt content of the protoplasm of
aquatic organisms.
•
Temperature variation is very low.
•
Less daylight penetration.
•
Influenced by climate and weather.
•
The largest variety of plants are algae, while others are seed plants.
•
Almost all animal phyla are found in freshwater. Organisms that live in freshwater are
generally adapted.
Adaptations of freshwater organisms are as follows:
a.
Plant adaptation
Plants that live in freshwater are usually one-celled and have strong cell walls such as
some blue algae and green algae. Water enters the cell to its maximum and stops itself.
Higher plants, such as lotus (Nymphaea gigantea), have anchor roots (vine roots).
Lower animals and plants that live in water habitat, its osmosis pressure is equal to the
osmosis pressure of the environment or isotonic.
b.
Animal adaptation
Freshwater ecosystems are inhabited by nekton. Nekton are animals that move actively
using strong muscles. Higher animals that live in freshwater ecosystems, such as fish,
in overcoming differences in osmosis pressure perform osmoregulation to maintain
water balance in their bodies through excretion, gills, and digestive systems. Freshwater
habitats are intermediate between marine and terrestrial habitats. The classification of
organisms in water can be based on energy flow and living habits.
B.
ECOSYSTEM CLASSIFICATION OF FRESHWATER ORGANISMS
1.
Based on energy flow, organisms are divided into autotrophs (plants), and phagotrophs
(macroconsumers), namely predatory carnivores, parasites, and saprotrophs or organisms that
live on the substrate of organismal remains.
2.
Based on living habits, organisms can be divided as follows.
a.
Plankton; consisting of phytoplankton and zooplankton; usually floating (passive
movement) following the motion of the water flow.
b.
Nekton; animals that actively swim in water, such as fish.
c.
Neuston; organisms that float or swim on the surface of water or rest on the surface of
water, such as aquatic insects.
d.
Periphyton; is a plant or animal that is attached/dependent on other plants or objects,
such as snails.
e.
Benthos; animals and plants that live on the bottom or live in sediment. Benthos can be
sessile (attached) or free-moving, such as worms and mussels.
C.
KINDS OF AQUATIC ECOSYSTEMS FRESH
Freshwater ecosystems are classified into still water (lentic) and flowing water (lotic).
Quiet water ecosystems include lakes and swamps, while flowing water ecosystems include
rivers.
1.
Lake
A lake is a body of stagnant water ranging in size from a few square meters to hundreds
of square meters. In the lake there is a division of areas based on sunlight penetration. Areas
that can be penetrated by sunlight so that photosynthesis occurs are called photic areas. Areas
that are not penetrated by sunlight are called aphotic areas. There are also areas of drastic
temperature changes or thermoclines. The thermocline separates the warm area at the top
from the cold area at the bottom.
Plant and animal communities are distributed in the lake according to its depth and
distance from the shore. Based on this, the lake is divided into 4 regions as follows.
a)
Littoral area
This area is a shallow area. Sunlight penetrates optimally. The warm water is close to the
edge. The plants are aquatic plants with roots and leaves that stick out above the water
surface. The community of organisms is very diverse including attached algae (especially
diatoms), various snails and mussels, insects, crustaceans, fish, amphibians, aquatic and semi-
aquatic reptiles such as turtles and snakes, ducks and geese, and some mammals that often
forage in the lake.
Natural Communities in the Littoral Zone
1.
Manufacturer
In the littoral area there are two main types of producers, namely the rooted plant group or
benthic group, which is generally Spermatophyta and phytoplankton which is generally
Algae.
2.
Consumer
The littoral zone is inhabited by a wide variety of animals, more than any other zone. Almost
all phyla that live in aquatic habitats are found here. Periphyton animals here show more
vertical zonation, such animals include: snails, worms, rotifers, flatworms, and various
larvae, as well as amphibians, reptiles, and pisces.
b)
Limnetic region
This area is an area of free water that is far from the edge and is still
permeable to sunlight. This area is inhabited by a variety of phytoplankton, including algae
and cyanobacteria. Algae photosynthesize and reproduce at high rates during summer and
spring. Zooplankton, which mostly include Rotifera and small crustaceans, prey on
phytoplankton. Zooplankton are eaten by small fish. Small fish are eaten by larger fish, and
large fish are eaten by snakes, turtles, and fish-eating birds.
c)
Profundal region
This area is the deep, aphotic region of the lake. Microbes and other organisms use oxygen to
cellular respiration after decomposing detritus falling from the limnetic region. Since there is
no light, the inhabitants of the profundal zone depend on the limnetic and littoral zones.
d)
Benthic area
This area is the bottom of the lake where benthos and the remains of dead organisms are
found.
Lakes can also be categorized based on their organic matter production, as follows:
a.
Oligotropic Lake
Oligotrophic is the name given to lakes that are deep and lack food, because
phytoplankton in the limnetic region are not productive. The water is very clear, inhabited by
few organisms, and at the bottom of the water there is a lot of oxygen throughout the year.
b.
Eutrophic Lake
Eutrophic is a term for lakes that are shallow and rich in food content, because
phytoplankton are very productive. The characteristics are that the water is murky, there are
various organisms, and oxygen is present in the profundal area. Oligotrophic lakes can
develop into eutrophic lakes due to incoming organic matter and sediment. This change can
also be accelerated by human activities, for example from the remnants of artificial
agricultural fertilizers and municipal waste piles that enrich the lake with nitrogen and
phosphorus discharges. This results in blooming algae populations, resulting in excessive
detritus production that eventually depletes the lake's oxygen supply. This enrichment of the
lake is called "eutrophication". Eutrophication makes the water unusable and reduces the
beauty value of the lake.
Based on the water circulation pattern, lakes in the world can be categorized into:
a.
Dimictic, in this type of lake there are two seasonal free circulation or two overturns.
b.
Monomictic cold, in this type of lake the water temperature is never above 4 C (polar
regions). There is one seasonal overturn in summer.
c.
Hot monomictic, in this type of lake the water temperature never goes below 4C
(subtropical region) there is one seasonal overturn in winter.
d.
Polymictic, in this type of lake there is almost always water circulation. Stagnation
periods, if any, are only short, found in high areas on the equator.
e.
Oligomictic, in this type of lake the mixing of water is very slow due to stable
temperatures. This type is found in many lakes in the tropics.
f.
Meromictic, in this type of lake there is permanent stratification, generally due to
chemical differences in the epilimnion and hypolimnion water layers.
2.
River
A river is a body of water that flows in one direction. River water is cold and clear and
contains little sediment and food. The constant flow of water and waves oxygenate the water.
Water temperature varies with altitude and latitude. Communities in rivers are different from
those in lakes. Fast flowing river water does not support the existence of a plankton
community to stay, because it will be carried away by the current. Instead, photosynthesis
occurs from attached algae and rooted plants, supporting the food chain. The composition of
the animal community also differs between the river, tributaries and downstream. In
tributaries, freshwater fish are often found. Downstream, catfish and carp are common. Some
large rivers are inhabited by various turtles and snakes. Especially in tropical rivers,
crocodiles and dolphins live there. River organisms can survive not being carried away by the
current because they are adapted to Evolutionary. For example, they are thin-bodied
dorsoventral and can cling to rocks. Some insect species that live on the downstream flanks
inhabit small habitats that are free from whirlpools.
The difference with lakes is:
•
The existence of current
•
Exchange between water and the bottom is more intensive due to currents
•
In running water, oxygen levels are higher than in still water
•
More even mixing of substance content, as well as temperature. Adaptation of lotic
(river) water organisms:
•
Permanently attached to a fixed substrate, e.g. rocks, plants
•
Has hooks or suction to attach to slippery places
•
The lower surface of the body can be used for attachment
•
Stream line body shape, slightly egg-like body shape rounded in front and flattened
posteriorly to reduce water pressure
•
Flat body shape, in addition to the stream line flat body shape so that it is easy to hide under
rocks
•
Positive rheotaxis, flowing water organisms always try to go against the current and this is in
contrast to still water organisms.
D.
ECOSYSTEM CHANGES AND ENVIRONMENTAL IMPACTS
Human activities and natural disasters can cause changes to an ecosystem. Natural
disasters, such as volcanic eruptions and earthquakes, are beyond human control. However,
human activities, such as pollution and over-exploitation of natural resources, will directly or
indirectly lead to ecosystem changes.
Destruction of a community's habitat will directly alter the ecosystem in that habitat.
For example, exploitation of fish in a lake or river using explosives, electric current or toxic
materials results in the destruction of the habitat of the community in the lake/river and
further causes ecosystem changes and a decrease in biodiversity. In freshwater ecosystems,
there are limiting factors that allow the mechanisms that take place in the ecosystem to run
steadily. These limiting factors are related to the condition of the freshwater habitat (aquatic
environment), namely:
1.
Temperature
2.
Transpiration
3.
Turbidity
4.
Current
5.
Mainstream gas in water
6.
Dissolved Oxygen (DO)
7.
Dissolved carbon dioxide
8.
Biogenic salts in water
9.
Na and K
10.
Calcium and Magnesium
11.
Phosphorus
12.
Water convection
The disruption of the above limiting factors, such as an increase or decrease in the
concentration and magnitude of these factors, will undoubtedly affect the community and
abiotic environment of the lake/river ecosystem. An example of a case due to water pollution
originating from the waste of a paper factory that has an adverse impact on the environment
and disturbance to the ecosystem is as follows:
1.
Disturbance to vegetation
Rice plants in paddy fields in polluted areas are often attacked by wilting disease with
symptoms of leaf tops drying and rotting and ending with the death of the plant.
2.
Disturbance to fauna
Animals and poultry that drink the polluted river water die or produce deformed offspring.
3.
Human disturbance
In cultivating rice fields, farmers have to change the way they plant rice, especially in
the dry season, because during the growing season there is a lot of paper layer that settles and
covers the surface of the soil; farmers have to provide extra labor to pick up the paper layer
that settles on the surface.
This means that the soil will increase the cost of production. From the above example,
it is clear that disturbance or pollution of the environment will result in changes to the
ecosystem.
