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Transcript
What are biogeochemical cycles? • Earth system has four parts – – – – Atmosphere Hydrosphere Lithosphere Biosphere • Biogeochemical cycles: The chemical interactions (cycles) that exist between the atmosphere, hydrosphere, lithosphere, and biosphere. • Abiotic (physio-chemical) and biotic processes drive these cycles • Focus on carbon, nitrogen, water cycles (but could include all necessary elements for life) What is common amongst them? • • • • • • Typical exist in all four parts of the Earth System There are ‘pools’ Are transformed chemically or biochemically There are fluxes between the pools Transformations are important Transformations can lead to positive and negative consequences Transformations Examples of Transformations 1. Carbon cycle: Organic compounds to CO2 (process: decomposition or fire) 2. Carbon cycle: CO2 to organic compounds (process: photosynthesis) 3. Nitrogen cycle: N2 to NO3 (atmospheric nitrogen to plant utilizable nitrate) (process: N-fixation) 4. Nitrogen cycle: N2 to NH3 (plant utilizable ammonia) (process: Haber-Bosch Industrial N-fixation) 5. Water cycle: Liquid water to water vapor (process: evaporation and evapo-transpiration) 6. Water cycle: Water vapor to liquid water (process: condensation) Carbon Cycle 760 5000 http://www.epa.gov/climatechange/kids/carbon_cycle_version2.html Key Aspects of the Carbon Cycle • Carbon is the skeleton of all life. • Carbon dioxide is a critical gas: – Taken up by plants in photosynthesis – Released by plants and animals in respiration – Released during decomposition (and fires) – Greenhouse gas (greenhouse effect - your car in the sun) Nitrogen Cycle Forms Sources of biologically Forms of&Nitrogen Losses of nitrogen from available systemnitrogen 1. N2 - inert gas, 78% of the atmosphere plants 2.For NO, N20, NO2 - other gases of nitrogen, not directly biologically important. Part •• NO In bogs, lakes of 3the gases found(places in smog. of low oxygen), NO3 is converted to N2 ++ -- ionic forms of nitrogen that are biologically usable. NH 3.• by NO4bacteria 3 and NH4 (get their oxygen from the NO3) • Sources: N-fixation by plants (N2 to NH3 and N2 to NO3), lightening, bacteria + (urea) • Volatilization of NH to ammonia decomposition of organic 4N (amino acids & proteins) gas (NH3) - warm, dry conditions. For animals of NO - (nitrate) • Leaching 3 • Organic forms: amino acids and proteins (from plants or other animals) • Erosion • Fire (combustion) http://soil.gsfc.nasa.gov/NFTG/nitrocyc.htm Nitrogen Sources over time Nitrogen Cycle: Key Points • Nitrogen is in the atmosphere as N2 (78%) • N2 is an inert gas and cannot be used by plants or animals • N2 can be converted to a usable form via – Lightening – N-fixing plants and cyanobacteria – Industrial process • Nitrogen limits plant growth Summary • • • • • 1. What are systems? 2. What are biogeochemical cycles? 3. Why are they important? 4. What is common about them? 5. Carbon and nitrogen cycles