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BIOgeochemical cycles

BIOgeochemical cycles. Biology 420 Global Change. Introduction. Remember Lithosphere Hydrosphere Atmosphere Biosphere Earth is exposed to cyclic phenomena Daily rotation/annual revolution Variations in orbit – glacial cycles Plant photosynthesis/respiration cycles Water cycle.

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BIOgeochemical cycles

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  1. BIOgeochemical cycles Biology 420 Global Change

  2. Introduction • Remember • Lithosphere • Hydrosphere • Atmosphere • Biosphere • Earth is exposed to cyclic phenomena • Daily rotation/annual revolution • Variations in orbit – glacial cycles • Plant photosynthesis/respiration cycles • Water cycle

  3. Generalized Biogeochemical Cycles • Major parts of the biosphere are connected by the flow of chemical elements and compounds. • Exchanges of materials between these different reservoirs • Between atmosphere and biota/oceans can be rapid • Between rocks, soils and oceans can be more slow. • What is being exchanged?

  4. Major Elements • Six elements account for 95% of biosphere • C, H, O, N, P, S • In 1958, Albert Redfield published a paper of great importance to marine biogeochemistry • Fairly constant molar ratio of N and P in phytoplankton • C106N16P (known as the Redfield Ratio) also C106O138N16P

  5. Major Element Cycles • There are others – iron, metals, Ca/Si for example • Here we will consider these: C, H, O, N, P, S • Water Cycle last time (H2O) • Today • Carbon Cycle • Nitrogen Cycle • Phosphorus Cycle • Sulfur Cycle

  6. Let’s Start with Carbon • More than 1 million known carbon compounds • Unique ability of carbon atoms to form long stable chains makes life possible • Oxidation states ranging from +IV to –IV • most common is +IV as in CO2 and carbonate • CO in trace levels in atmosphere is +II • Assimilation of carbon by photosynthesis creates reduced carbon CH2O • CH4, also trace gas is –IV

  7. More on Carbon • Seven isotopes of carbon

  8. Carbon Reservoirs • Reservoir: In geochemistry, a reservoir is the mass of an element (such as carbon) or a compound (such as water) within a defined “container” (such as the ocean or the atmosphere or the biosphere). • Atmosphere • CO2 – based on a CO2 concentration of 351.2 ppmv in 1988  corresponds to 747 Pg of carbon (1 Pg= 1015g) • CH4 – based on CH4 concentration of 1.7 ppmv in 1988  corresponds to 3 Pg of carbon (most abundant organic trace gas and 2nd most important changing greenhouse gas) • CO –ranging from 0.05 to 0.20 ppmv 0.2 Pg carbon • Hydrosphere (oceans) • Dissolved inorganic carbon (DIC)  37,900 Pg C • Dissolved organic carbon (DOC)  1000 Pg C • Particulate organic carbon (POC)  30 Pg C • Marine biota  3 Pg C • Terrestrial Biosphere ranging from 480 – 1080 Pg C • Lithosphere – carbon in rocks, fossil fuels  huge reserves 20 million Pg C in rocks, 104 Pg C in extractable reserves of oil and coal

  9. Carbon Flux

  10. Nitrogen • Coupled with other elements of living matter (such as carbon) • Important biological and abiotic processes • Oxidation states from +V to –III • Not found in native rocks, major reservoir is N2 in atmosphere • Biological Transformation of Nitrogen Compounds (microbial mediation) • Nitrogen fixation  enzyme-catalyzed reduction of N2 to NH3, NH4+ or any organic nitrogen • Ammonia assimilation  uptake of NH3, NH4+ • Nitrification  oxidation of NH3, NH4+to NO2- or NO3- as a means of producing energy • Assimilatory nitrate reduction  reduction of NO3- then conversion to biomass • Ammonification organic nitrogen to NH3 or NH4+ • Denitrification reduction of NO3- to N2 or N2O (nitrous dioxide, gaseous forms)

  11. Reservoirs and Fluxes

  12. More Nitrogen • NOx • NO (nitric oxide) and NO2 (nitrogen dioxide) • Formed due to reactions of N and O in air during combustion • Air pollution and reactions to form acid rain • Atmospheric deposition: elements of biogeochemical interest deposited on Earth as • rainfall • dry deposition (sedimentation) • direct adsorption of gases

  13. Processes of Nitrogen Gas Emissions • Rapid conversion of NH4+ to NH3 at high pH and low soil moisture  results in gas loss to atmosphere • High organic waste loads (from feedlots) promote NH3 loss • NO, N2O are byproducts of nitrification • NO, N2O and N2 are products of denitrification • Atmospheric N Deposition • Acidic wet and dry deposition due to combustion • NH4+ from livestock organic waste

  14. Wet Deposition NO3/NH4 (2009)

  15. Phosphorus • Second most abundant mineral in human body (surpassed only by Ca) • This cycle has no atmospheric component (gaseous P3 is negligible) • Restricted to solid and liquid phases (many mineral reactions) • Unlike nitrogen, not really involved in microbial reactions • Oxidation-reduction reactions play a minor role in reactivity and distribution of phosphorus • Only 10% of phosphorus from rivers to oceans is available to marine biota • It is suggested that terrestrial net primary productivity is determined by level of available phosphorus in soil • P in low concentrations in rocks • N abundant in atmosphere • Other essential plant nutrients are more abundant than P (S, K, Ca, Mg) • Bacteria involved in N cycle require P also

  16. More on Phosphorus Forms • Dissolved Inorganic Phosphorus  PO43- • Organic Forms phosphate in DNA, RNA, ATP, phospholipid • Minerals  apatite [Ca(PO4)3OH] • Distribution • Sediments 4 million Pg P • Land 200 Pg P • Deep Ocean 87 Pg P • Terrestrial Biota 3 Pg P • Surface Ocean 2.7 Pg P • Atmosphere 0.000028 Pg P

  17. Phosphorus Cycle • A “sedimentary” cycle with Earth’s crust as reservoir  erosion processes they are washed into rivers and oceans • Plant and animals  adsorption up the food chain… small role in comparison to 1st point • Agriculture  a limiting nutrient • Mined for fertilizer • Form of fertilizer is phosphate • Also contain nitrogen

  18. Sulfur Cycle • Essential to life, also relatively abundant and thus not limiting • Like phosphorus, has important geochemical cycling • Like nitrogen • Important gas phases • Oxidation-reduction reactions and oxidation state from -II to +VI

  19. Sulfur Cycle

  20. Sulfur Reservoirs • The crust  as gypsum (CaSO4) and pyrite (FeS2) • Distribution • Lithosphere: 2 x 1010Tg S • Ocean: 1.3 x 109Tg S • Ocean Sediments: 3 x 109Tg S • Marine Biota: 30 Tg S • Soils and Land Biota: 3 x 105Tg S • Lakes: 300 Tg S • Continental Atmosphere: 1.6 Tg S • Marine Atmosphere: 3.2 Tg S

  21. Sources of Sulfur in Atmosphere • Volcanic eruptions • 12-30 Tg S averaged over many years • Tambora, Indonesia in 1815, 1816 – year without summer ~50 Tg S • Soil dust • Biogenic gases • Anthropogenic emission

  22. Marine Sulfur Cycle • Ocean is large source of aerosols (sea salts) that contain SO42- (mostly re-deposited onto ocean) • DMS • dimethyl-sulfide (CH3)2S is a major biogenic gas emitted from sea • Produced during decomposition of dimethyl-sulfonpropionate (DMSP) from dying phytoplankton • Small fraction is lost to atmosphere • Oxidation of DMS to sulfate aerosols  greater cloud condensation nuclei  more clouds • Layer of sulfate aerosols (Junge layers) 20-25 km altitude

  23. Microbial Action • Assimilative reduction of SO4- to –SH groups in proteins • Release of –SH to form H2S during excretion, decomposition and desulfurylation • Oxidation of H2S by chemolithotrophs to form elemental sulfur or SO4- • Dissimilative reduction of SO4- by anoxygenic phototrophic bacteria

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