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BIOGEOCHEMICAL CYCLES Biology 420 Global Change. Introduction  Remember  Lithosphere  Hydrosphere  Atmosphere  Biosphere  Earth is exposed to cyclic.

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Presentation on theme: "BIOGEOCHEMICAL CYCLES Biology 420 Global Change. Introduction  Remember  Lithosphere  Hydrosphere  Atmosphere  Biosphere  Earth is exposed to cyclic."— Presentation transcript:

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 C 106 N 16 P (known as the Redfield Ratio) also C 106 O 138 N 16 P

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 (H 2 O)  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 CO 2 and carbonate  CO in trace levels in atmosphere is +II  Assimilation of carbon by photosynthesis creates reduced carbon CH 2 O  CH 4, 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  CO 2 – based on a CO 2 concentration of ppmv in 1988  corresponds to 747 Pg of carbon (1 Pg= g)  CH 4 – based on CH 4 concentration of 1.7 ppmv in 1988  corresponds to 3 Pg of carbon (most abundant organic trace gas and 2 nd 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, 10 4 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 N 2 in atmosphere  Biological Transformation of Nitrogen Compounds (microbial mediation)  Nitrogen fixation  enzyme-catalyzed reduction of N 2 to NH 3, NH 4 + or any organic nitrogen  Ammonia assimilation  uptake of NH 3, NH 4 +  Nitrification  oxidation of NH 3, NH 4 + to NO 2 - or NO 3 - as a means of producing energy  Assimilatory nitrate reduction  reduction of NO3- then conversion to biomass  Ammonification  organic nitrogen to NH 3 or NH 4 +  Denitrification  reduction of NO 3 - to N 2 or N 2 O (nitrous dioxide, gaseous forms)

11 Reservoirs and Fluxes

12 More Nitrogen  NOx  NO (nitric oxide) and NO 2 (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 NH 4 + to NH 3 at high pH and low soil moisture  results in gas loss to atmosphere  High organic waste loads (from feedlots) promote NH 3 loss  NO, N 2 O are byproducts of nitrification  NO, N 2 O and N 2 are products of denitrification  Atmospheric N Deposition  Acidic wet and dry deposition due to combustion  NH4 + from livestock organic waste

14 Wet Deposition NO 3 /NH 4 (2009)

15 Phosphorus  Second most abundant mineral in human body (surpassed only by Ca)  This cycle has no atmospheric component (gaseous P 3 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  PO 4 3-  Organic Forms  phosphate in DNA, RNA, ATP, phospholipid  Minerals  apatite [Ca(PO 4 ) 3 OH]  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 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 1 st 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 (CaSO 4 ) and pyrite (FeS 2 )  Distribution  Lithosphere: 2 x Tg S  Ocean: 1.3 x 10 9 Tg S  Ocean Sediments: 3 x 10 9 Tg S  Marine Biota: 30 Tg S  Soils and Land Biota: 3 x 10 5 Tg 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  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 SO 4 2- (mostly re-deposited onto ocean)  DMS  dimethyl-sulfide (CH 3 ) 2 S 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) 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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