ECOSYSTEM ECOLOGY Ecosystem ecology Chapter 55 Study of biological communities and abiotic environment Thermodynamics First Law of Thermodynamics - Energy is neither created nor destroyed Second Law of Thermodynamics - With each successive energy transfer, less energy is available to perform work or energy transfer is not 100% efficient or entropy increases Energy Energy moves through ecosystems Living organisms require a constant input of energy, since they are ordered Energy must be supplied from an external source to keep biological processes running 1
Energy budgets and productivy vary Energy transfer is not 100% efficient Pyramids result 2
Law of conservation of mass Matter can neither be created or destroyed Generalized materials cycle Hydrologic cycle Most water is stored in the oceans Solar energy continually evaporates water stored in the oceans and land, and distributes water vapor around the globe Condenses over land surfaces, supporting all terrestrial systems 3
The hydrologic cycle Human impacts on the hydrologic cycle Damming rivers slows water and increases evaporation Removal of vegetation increases runoff and erosion while decreasing infiltration and transpiration Overdrawing surface and groundwater lowers water tables Carbon cycle The carbon cycle Carbon is a structural component of organic molecules and provides metabolic energy Begins with intake of CO 2 during photosynthesis. Carbon atoms are incorporated into glucose and then: Remain in plant material until death, eaten, respired, excreted Decomposition returns carbon to the sediment, the largest reservoir of carbon Fossil fuels are carbon sink Oceans are second largest reservoir of carbon Humans affect the carbon cycle Burning fossil fuels moves carbon from the ground to the air Since mid-1700s, people have added over 275 billion tons of carbon dioxide to the atmosphere Cutting forests and burning fields moves carbon from organisms to the air Less carbon dioxide is removed by photosynthesis Today s atmospheric carbon dioxide reservoir is the largest in the past 800,000 years The driving force behind climate change The nitrogen cycle involves bacteria Nitrogen is contained in proteins, DNA, and RNA Nitrogen makes up 78% of the atmosphere Nitrogen is inert gas and cannot be used by organisms 4
Nitrogen must become biologically available Nitrogen-fixing soil bacteria or lightning fixes nitrogen gas into ammonium Nitrogen-fixing bacteria live in legumes (e.g., soybeans) Bacteria then convert ammonium ions first into nitrite ions then into nitrate ions through process of nitrification Plants can take up these ions Nitrite and nitrate also come from pollution Animals obtain nitrogen by eating plants or other animals Denitrifying bacteria convert nitrates in soil or water to gaseous nitrogen, releasing it back into the atmosphere The nitrogen cycle Humans greatly affect the nitrogen cycle The phosphorus cycle Historically, nitrogen fixation limited the flux of nitrogen from air into water-soluble forms Industrial fixation fixes nitrogen on a massive scale Overwhelming nature s denitrification abilities Excess nitrogen leads to hypoxia (no oxygen) in coastal areas Burning forests and fossil fuels leads to acid precipitation, adds greenhouse gases, and creates photochemical smog No significant atmospheric component Most phosphorus is in rocks Weathering releases phosphorus into water The phosphorus cycle Humans affect the phosphorus cycle Fertilizer from lawns and farmlands Increases phosphorus in soil Runoff increases phytoplankton blooms and hypoxia Wastewater containing detergents releases phosphorus to waterways 5
atmosphere respiration atmosphere photosynthesis creosote bush prairie dog creosote bush prairie dog coyote coyote Here lies Grandma Johnson Here lies Grandma Johnson respiration Grandma Johnson worms Grandma Johnson decomposers Ecosystems retain nutrients Increasing temperatures change nutrient cycling Bioremediation removes contaminants Restoration ecology seeks to repair ecosystems 6
7