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Biological Sciences
Mary Olaveson

Chapter 56 – Ecosystem & Global Economy Unlike energy, which is lost as it travels up the trophic levels; chemical compounds remain unchanged and can be reused, in processes which are often cyclic The movement of energy and materials on Earth is between 4 compartments: Oceans, Fresh Waters, Atmosphere, and Land Oceans At one point or another, most materials that cycle through the four compartments end up in oceans Despite their massive size, oceans only exchange materials with the atmosphere on the surface therefore they respond very slowly from input of other departments In most of the oceans, there is very slow mixture. Most material sink to the bottom and stay there for millions of years, however sometimes the material is brought back up to surface water, causing upwelling zones which support high rates of photosynthesis Freshwater Freshwater consists of rivers, lakes, and groundwater. Water travels very fast through them In lakes, minerals and nutrients are taken up by organisms which they incorporate into their cells. Once these organisms die, they take with them the nutrients and minerals. Often, deteritivores consume the oxygen by eating their tissues Therefore the surface waters of lakes quickly become depleted of nutrients while deeper waters become depleted of oxygen This is often resolved by a process known as turnover, which brings nutrients to the surface of lakes and oxygen to the bottom of the lakes Turnovers in shallow lakes are driven by winds whereas in deep lakes, it is driven by temperature In the case of deep lakes, turnovers occur because water is at its densest at 4®, anything above or below that causes it to expand. Therefore in the winter, the coldest waters float to the surface and are usually covered by ice and the waters below remains at 4®. When spring comes and ice melts, the surface also becomes 4®. At this point all the water is uniform and the wind can mix the water, allowing nutrients to float to the top and oxygen to reach the bottom SEE FIG. 56.3 Atmosphere The atmosphere is a thin layer of gas surrounding Earth that contains the highest levels of nitrogen (78.08%) and oxygen (20.95%) of anywhere on Earth Troposphere: the lowest layer of the atmosphere. Contains 80% of the atmospheric mass. Also, most global air circulation is found in this level as well as virtually all the water vapour 10-17km from Earth’s surface Stratosphere: Extends from the top of the troposphere to 50 km above Earth’s surface Material enters the stratosphere through the troposphere in the inter-tropical convection zone, where hot air raises to high altitudes A layer of ozone in the stratosphere absorbs most of the biologically damaging short wavelength UV radiation entering the atmosphere Also, it has an important role in temperature regulation because it is transparent to light however it traps heat and doesn’t allow it to leave Greenhouse Gases: Chemical gases which are especially good at trapping heat. I.e. carbon dioxide Land Covers about 25% of earth’s surface The terrestrial compartment is connected to the atmosphere by organisms that take chemical elements from, and release them back into the atmosphere It is connected to oceans by the soils which are carried into the ground water and eventually into the oceans Although land covers a small amount of Earth’s surface, much of life depends on the soil’s fertility and the productivity of terrestrial ecosystems Solar Energy All energy utilized by organisms has come from the sun (with the exception of few ecosystems like caves, deep sea hydrothermal vents, etc) Solar energy enters ecosystems by way of plants and other photosythesizer organisms. Despite that, only 5% of all the solar energy that hits Earth is captured by photosynthesis. The rest is reradiated back into the atmosphere or taken up by chemical compounds Gross Primary Productivity (GPP): The rate at which energy is incorporated into the bodies of photosynthetic organisms (primary producers) Gross Primary Production: the accumulated energy of GPP GPP is the rate; gross primary production is the product Net Primary Production (NPP): The amount of energy available to a primary consumer. It is the gross primary production minus the amount of energy expanded on its own metabolism Only the NPP is available to organisms consuming it The geographic distribution of the energy assimilated by primary producers depends on the distribution of land mass, temperature, moisture etc. Those areas with adequate factors such as the tropics thrive in ecosystem productivity while other areas that do not possess these factors do not thrive (i.e. desserts, poles) Human advances change the way GPP and NPP is used by other organisms and its distribution in both good ways (increased agriculture) and bad ways (cutting down forest fo
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