biogeochemical cycles

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BIOGEOCHEMICAL CYCLES Biology 420 Global Change

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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. - PowerPoint PPT Presentation

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Page 1: BIOgeochemical  cycles

BIOGEOCHEMICAL CYCLESBiology 420 Global Change

Page 2: BIOgeochemical  cycles

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

Page 3: BIOgeochemical  cycles

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?

Page 4: BIOgeochemical  cycles

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

Page 5: BIOgeochemical  cycles

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

Page 6: BIOgeochemical  cycles

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

Page 7: BIOgeochemical  cycles

More on Carbon Seven isotopes of carbon

Page 8: BIOgeochemical  cycles

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

Page 9: BIOgeochemical  cycles

Carbon Flux

Page 10: BIOgeochemical  cycles

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)

Page 11: BIOgeochemical  cycles

Reservoirs and Fluxes

Page 12: BIOgeochemical  cycles

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

Page 13: BIOgeochemical  cycles

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

Page 14: BIOgeochemical  cycles

Wet Deposition NO3/NH4 (2009)

Page 15: BIOgeochemical  cycles

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

Page 16: BIOgeochemical  cycles

More on Phosphorus Forms Dissolved Inorganic Phosphorus PO4

3-

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

Page 17: BIOgeochemical  cycles

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

Page 18: BIOgeochemical  cycles

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

Page 19: BIOgeochemical  cycles

Sulfur Cycle

Page 20: BIOgeochemical  cycles

Sulfur Reservoirs The crust as gypsum (CaSO4) and pyrite (FeS2) Distribution

Lithosphere: 2 x 1010 Tg S Ocean: 1.3 x 109 Tg S Ocean Sediments: 3 x 109 Tg S Marine Biota: 30 Tg S Soils and Land Biota: 3 x 105 Tg S Lakes: 300 Tg S Continental Atmosphere: 1.6 Tg S Marine Atmosphere: 3.2 Tg S

Page 21: BIOgeochemical  cycles

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

Page 22: BIOgeochemical  cycles

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

Page 23: BIOgeochemical  cycles

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