Tina Salmassi - Lecture - Biogeochemical Cycles

8/13/2019 Tina Salmassi - Lecture - Biogeochemical Cycles

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BIOGEOCHEMICAL CYCLES

Biology 420 Global Change


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Introduction

! Remember! Lithosphere! Hydrosphere! Atmosphere! Biosphere

! Earth is exposed to cyclicphenomena! Daily rotation/annual revolution

" Variations in orbit glacialcycles

! Plant photosynthesis/respirationcycles

! Water cycle


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Generalized Biogeochemical Cycles

! Major parts of thebiosphere are connected bythe flow of chemicalelements and compounds.

! Exchanges of materialsbetween these differentreservoirs

! Between atmosphere andbiota/oceans can be rapid

! Between rocks, soils andoceans can be more slow.

! What is being exchanged?


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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


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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


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Lets Start with Carbon

! More than 1 million knowncarbon compounds

! Unique ability of carbon atomsto form long stable chains

makes life possible! Oxidation states ranging from

+IV to IV! most common is +IV as in CO2and

carbonate

! CO in trace levels in atmosphere is+II

! Assimilation of carbon byphotosynthesis creates reducedcarbon CH2O

! CH4, also trace gas is IV


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More on Carbon

! Seven isotopes of carbon


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Carbon Reservoirs

! Reservoir: In geochemistry, a reservoir is the mass of an element (such as carbon) ora compound (such as water) within a defined container (such as the ocean or theatmosphere or the biosphere).

! Atmosphere! CO2 based on a CO2concentration of 351.2 ppmv in 1988 #corresponds to 747 Pg

of carbon (1 Pg= 1015g)

! CH4 based on CH4concentration of 1.7 ppmv in 1988#corresponds to 3 Pg of carbon(most abundant organic trace gas and 2ndmost 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,

104Pg C in extractable reserves of oil and coal


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Carbon Flux


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Nitrogen

! Coupled with other elements of living matter (such ascarbon)

! Important biological and abiotic processes! Oxidation states from +V to III! Not found in native rocks, major reservoir is N2in

atmosphere! Biological Transformation of Nitrogen Compounds

(microbial mediation)

! Nitrogen fixation#enzyme-catalyzed reduction of N2to 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 NH3or NH4+! Denitrification#reduction of NO3-to N2or N2O

(nitrous dioxide, gaseous forms)


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Reservoirs and Fluxes


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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 ofbiogeochemical interest deposited on Earth as

! rainfall! dry deposition (sedimentation)! direct adsorption of gases


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Processes of Nitrogen Gas Emissions

! Rapid conversion of NH4+to NH3at high pH andlow soil moisture#results in gas loss to atmosphere

! High organic waste loads (from feedlots) promoteNH3loss

! NO, N2O are byproducts of nitrification! NO, N2O and N2are products of denitrification! Atmospheric N Deposition! Acidic wet and dry deposition due to combustion! NH4+from livestock organic waste


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Wet Deposition NO3/NH4(2009)


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Phosphorus

! Second most abundant mineral in human body (surpassed only by Ca)! This cycle has no atmospheric component (gaseous P3is 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


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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


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Phosphorus Cycle

! A sedimentary cycle withEarths crust as reservoir #erosion processes they arewashed into rivers and oceans

! Plant and animals #adsorption up the foodchain small role incomparison to 1stpoint

! Agriculture#a limitingnutrient! Mined for fertilizer! Form of fertilizer is phosphate! Also contain nitrogen


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Sulfur Cycle

! Essential to life, also relatively abundant and thus notlimiting

! Like phosphorus, has important geochemical cycling! Like nitrogen

! Important gas phases! Oxidation-reduction reactions and oxidation state from -II to +VI


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Sulfur Cycle


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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


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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


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Marine Sulfur Cycle

! Ocean is large source of aerosols (sea salts) thatcontain SO4

2-(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


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Microbial Action

! Assimilative reduction of SO4- to SH groups inproteins

! Release of SH to form H2S during excretion,decomposition and desulfurylation

! Oxidation of H2S by chemolithotrophs to formelemental sulfur or SO4-

! Dissimilative reduction of SO4- by anoxygenicphototrophic bacteria

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Tina Salmassi - Lecture - Biogeochemical Cycles