24.Biogeochem.cycling.15 - Special Topic Biogeochemical...

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Special Topic: Biogeochemical Cycling Introduction Nitrogen Cycle Sulfur Cycle Mercury Cycle Arsenic Cycle Summary and Conclusions
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I. What is Biogeochemical Cycling? Natural recycling of elements in via biological, geological and chemical processes Involves transport and transformation of substances in the environment Many cycles are interconnected: carbon, sulfur, nitrogen, etc. Cycles facilitate prediction of the fate of some chemicals – they essentially jump on the “environmental merry-go-round”
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II. Nitrogen Cycle All life requires N-containing organics (e.g. amino acids, proteins, enzymes and nucleic acids) Air (78% N 2 ), is the major reservoir for N in the environment N 2 is not available for use by most organisms – plants must secure N in "fixed" form: NO 3 , NH 4 + and urea (NH 3 ) 2 CO Animals derive N (amino acids, proteins, etc.) via diet
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Four Main Processes Fixation – microbial absorption of atmospheric N 2 and conversion to ammonium (NH 4 + ) or amino acids Ammonification (microbial decay) – reduction of amino acids to ammonium (NH 4 + ) Nitrification – oxidation of ammonium to NO 2 - and NO 3 - Denitrification – conversion of NO 2 - and NO 3 - to N 2 which returns to the atmosphere
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Nitrogen Cycle
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