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)