env330

ENV330 Module 2b AVP Transcript Slide 1 Title: Biogeochemical Cycles Narrator: Everything on the Earth, in the air, in the water, and below the surface of the Earth is recycled in great cycles involving Life, Rocks, Air, Water and the molecules and atoms which make them up. The familiar water or hydrologic cycle is a good example of these cycles. Most of the world’s water is found in the oceans which cover almost ¾ the of the planet with an average depth of 2 ½ miles. Radiant energy from the sun – sunlight – is converted into heat energy when it interacts with the surface of the Earth, including water. The heat energy causes some of the water molecules to evaporate and form water vapor; clouds, which move around the Earth with wind currents. When precipitation occurs in the form of rain, snow, hail, etc., the water vapor is converted back into liquid or solid water (ice) and gravity pulls it back down to the surface of the Earth where it either stays frozen as part of glaciers in high mountains, or as part of the frozen polar ice caps, or is absorbed as liquid water into the land and rivers and lakes. Plants absorb some of the water and animals drink some and eat the plants and so it enters into the food webs and ecosystems. All of the water is pulled by gravity across the land towards the lowest places, forming rivers and eventually flowing to the sea. Some of the water trickles down through layers of soil and rock to become ground water – aquifers, which also move slowly underground toward the oceans. Water is also evaporated from plants, rivers and lakes back into the atmosphere. Note that this cycle has been affected, as have all the biogeochemical cycles, by human activities. Some of the impacts include: Reduced recharge of land and flooding from covering land with buildings and crops, increased flooding from wetlands destruction, point source pollution of surface waters by industrial discharges, non-point source runoff of pollutants into waterways, aquifer depletion from over-pumping of wells, and, dramatic changes in rainfall patterns and melting of ice caps and glaciers due to global climate change. Another biogeochemical cycle, the carbon cycle is critical to all of life on Earth, since C is the atomic backbone of all the organic molecules which make up the cells of all living things. It is also critically important in its role related to Global Climate Change due to human activities. Most of Earth’s C is found as CO2 in the atmosphere. Plants take up the CO2 and use the C to build their bodies. This is called the “fixing” of C. Animals eat the plants and each other and decomposers eat both, thus spreading the carbon – the basis of all organic molecules that make up life – throughout all ecosystems. When animals and decomposers exhale they release CO2 back into the atmosphere. Some C is stored deep in the rocks as coal, natural gas and oil. This C was part of the partially decomposed organic matter from productive ecosystems like marshes and swamps where layers and layers of leaves and other biological debris form rich, deep black muck and peat which over the millions of years, if covered by other sediments, can become converted into “fossil fuels” – ancient stored sunlight! The photosynthesis of plants converts light energy into chemical energy. Coal, natural gas and oil are the ancient chemical energy made by ancient plants using ancient sunlight. CO2 is also dissolved into the oceans where ecosystems use it just as on the land. In addition, many marine organisms absorb C dissolved in the oceans as CaCO3 (calcium carbonate) to make their shells and other hard parts. The shells of clams and oysters, and many of the myriad plankton are made of CaCO3 , as are the skeletons of coral organisms. When these organisms die, especially the plankton, their limestone shells accumulate on the seafloor by the billions and over geological time become cemented together to form limestone rock layers miles deep. Tectonic movement of crustal plates can

result in the uplifting of this limestone rock which can then become part of the continents where they may be eroded by surf and wind and rivers, thus releasing the C back into the waters and soil where it may be taken up by plants once again. Some CO2 is released to the atmosphere from volcanic activity, as has always been the case on Earth. There are many harmful impacts of human activities on the Carbon Cycle which have led to a dramatic increase in the atmospheric CO2 concentrations, which is the main cause of Global Climate Change. Starting with agriculture some 10-12,000 years ago, humans began to burn down forests in order to plant crops. The combustion of wood converts the tons of C in organic molecules that make up the trees into CO2. During the industrial revolution starting in the 18

th century, millions of tons of coal were burned to

power the factories and mills and steam engines. Coal is a fossil fuel made up of C. The combustion of coal results in the release of tons of CO2 into the atmosphere. Oil was discovered in Pennsylvania in 1859. Billions of barrels of oil have been combusted since resulting in a catastrophic increase in atmospheric CO2 levels. The concentration of CO2 in the atmosphere today is dramatically higher than it has been on Earth for the last 900,000 years. Other important biogeochemical cycles include the N cycle, the P cycle and the S cycle. The Nitrogen cycle is also critical for life on Earth. Without N there would be no protein or enzymes. Without proteins and enzymes there would be no life. Most of the N on Earth is in the atmosphere. Soil bacteria play a critical role in making this cycle function. Human activities have also caused many disruption of this cycle, including fertilizer runoff into waterways resulting in fish kills. The Phosphorous cycle is additionally critical to life. Without P the energy transformation reactions that take place in every cell would be impossible. Most of the P on Earth is in certain sedimentary rocks associated with bird guano! Note again, that many disruptions of this cycle are caused by human activities. Sulfur is another important component of living organisms. The sulfur cycle is also degraded and altered by human activities which cause acid rain deposition leading to deforestation and the acidification of lakes. All the biogeochemical cycles are interconnected with each other and with the rock cycle and atmospheric and oceanic circulation. All of these critical biogeochemical cycles are being disrupted by human activities. In this course we will learn how to interact with these important cycles in a more responsible and sustainable way. End of Presentation