Lecture 19 Biogeochemical Cycles

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19 Apr 2012
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Lecture 19 BIO220 Biogeochemical Cycles
Nuclear weapons and ecological research, radiation effects on organisms, ecosystems
Nuclear research gave ecological tools and a model
Radioactive tracers allowed following fates of chemicals in natural communities
Chemistry of natural world
Large organic molecules: synthesized, consumed, broken down
Chemical elements not created/destroyed, they cycle
Cycle: pools, fluxes
C/N/P cycles
Tied to hydrologic cycle
N/P limit plant productivity
C Cycle
CO2, C in organisms, inactive sedimentary pool of carbonates
Limited by balance between creation (photosynthesis) and respiration/combustion
Human intervention: combustion of fossil fuels, land conversion
Agricultural impacts on C
Human deforestation
C in trees released by fire
Forest clearance: more pollen from open-country species rather than woodland
species
Current deforestation mainly in tropics
Tropical forests contain great store of C
Human effects on C budget
Larger compounds CO2 release
Strengthening greenhouse effect
N Cycle
Mostly gaseous compounds, high solubility, minimal sediment pools
Limited by N2 usable soluble nitrate/ammonium
Human intervention: combustion of fuels, energy to make synthetic fertilizers
N chemistry
Fixation: N2NH3 requires energy by eubacteria, cyanobacteria, lightning
Nitrification: NH4+ NO3- (nitrate)
Denitrification: NO3- N2
Can make N fertilizers by fixing N2 with electricity, natural gas
Human intervention in N cycle
Atmospheric cycle (fast)
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