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BGC- day 2

BGC- day 2. Nitrogen, Sulfur and Mercury Biogeochemical Cycles. Nitrogen Cycle. Limiting Nutrient (on land) Amino acids Nucleic acids (DNA/RNA) 3% by mass 78% atmosphere = N 2 FIXATION: N 2  NH 3 by cycanobacteria & legumes, then NH 4 + into soils. Nitrogen Cycle- 5 steps.

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BGC- day 2

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  1. BGC-day 2 Nitrogen, Sulfur and Mercury Biogeochemical Cycles

  2. Nitrogen Cycle • Limiting Nutrient (on land) • Amino acids • Nucleic acids (DNA/RNA) • 3% by mass • 78% atmosphere = N2 • FIXATION: N2 NH3 by cycanobacteria & legumes, then NH4+ into soils

  3. Nitrogen Cycle-5 steps • Fixation (atmosphere-->soil) • Assimilation (soil into biological organisms) • Ammonification (biological --> inorganic) • Nitrification (in soil) • Denitrification (back to atmosphere)

  4. (1)N-Fixation • unuseable --> useable form by organisms • Lightning/Combustion • Cyanobacteria • Fix in absence of oxygen

  5. (1)N-Fixation • Legume plants • Mutualistic relation with Rhizobium • Nodules

  6. (1) Fixation • N2 fixed abiotically in nature: N2 NO3- • Lightning • Combustion • Humans synthesize fertilizers from N2

  7. (2)Assimilation • ammonia, ammonium and nitrates into plant tissues • creation of biological nitrogen compounds

  8. (3)Ammonification • biological nitrogen compounds back to NH3& NH4+ • organic to inorganic form • Wastes have urea (urine & scat) • Decomposers • Ammonifying bacteria

  9. (4)Nitrification • NH4+ to NO2-to NO3- • Nitrifying bacteria • NO3- LEACHES through soil

  10. (5)Denitrification • Conversion of NO3-to N2O to N2 • Denitriying bacteria (O2 free areas)

  11. Nitrogen Cycle

  12. Nitrogen Cycle

  13. Human Impacts-N • Human Produced: Commercial Fertilizer overuse (fixed-N) = mobility • Eutrophication & fish kills • Groundwater contamination

  14. Human Impacts-N • Combustion of Fossil Fuels • NOx and autos • Global warming & Ozone depletion • Photochemical smog • Acid rain

  15. Human Impacts-N • In the 20th century, humans have doubled the amount of fixed nitrogen entering the global nitrogen cycle (source: R&B:p.108) • Half the fertilizer used in history have been applied since 1984 (source: NYT: 12/10/1996)

  16. S in Living Organisms • Plants uptake SO42- • S for proteins • Dimethyl sulfide (DMS) forming clouds and SO42- • BACTERIA drive the cycle: SO42- to H2S or to metallic S • “Chemosysnthesis”

  17. Sulfur Cycle • Source: rock deposits bound as minerals • Sea spray, dust storms (CaSO4) and volcanoes • atmosphere: H2S ---> SOx --> H2SO4

  18. Human Impact-S • Fossil Fuels: Coal & Diesel burning -->SO2 • Smelting of ores (FeS --> Fe + SOx) • Ice cores show Industrial revolution trend • Mined for H2SO4 industrial processes • biomining for metals in low-grade ores

  19. Why Care About mercury? • It is so “trace” • Mercury is one part per hunderedthousanth by mass. If a power plants burns 14,00 tons of coal a day, how many pounds (lbs) of mercury is released into the atmosphere? (given 2,000 lbs in one ton)

  20. Human Impacts-Hg • Burning Coal (1 plant - 170 lbs/yr) • Smelting Ores • Incineration • Mining Au • Vaccines

  21. Example: Minamata Bay Japan

  22. Proof Positive Proof Positive

  23. Mercury Cycle • Sources: Rocks and Coal • Sinks: sediments (?organisms?) • Inorganic mercury • Organic mercury: methylmercury

  24. MOVIE: Humans Mitigating Climate Change-Geoengineering

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