Download presentation
Presentation is loading. Please wait.
Published byAlina Ogburn Modified over 9 years ago
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 351.2 ppmv in 1988 corresponds to 747 Pg of carbon (1 Pg= 10 15 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 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 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 10 10 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 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 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) 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
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.