Chapter 22 Biogeochemical cycling

The Universe When? How? 15 X 109 years ago Matter existed in its most fundamental form. Elements formed as universe expanded and cooled. 13.8 sec post ‘Big Bang’ –formation of H and He nuclei 700,000 years later—electrons attached to nuclei

Formation of elements Elemental formation is linked to evolution of stars. Stars derive energy from nuclear reactions that synthesize elements. 4He + 4He  8Be 8Be + 4He  12C 1H + 4He  5Li 12C + 4He  16O

Ecosystems are linked Input and output of nutrients link ecosystems Gaseous cycle— atmosphere and ocean Sedimentary cycle— soil, rocks and minerals dissolved salts and rock phase

Carbon Basic element of all organic compounds Inseparable with energy flow Source of CO2 atmosphere/water Primary producers decomposers

Net ecosystem productivity Rate at which C is taken up in photosynthesis and lost due to respiration. Determined by Primary production Decomposition Terrestrial ecosystems—slower in cooler climates— slower decomposition and production

Aquatic C cycling Phytoplankton uses CO2 or carbonate CO2 enters back into system through respiration and decomposition

Variation in C cycling Varies with time of day— photosynthesis highest in afternoon respiration highest just before daylight Seasonal variation— varies according to weather varies with climate varies with seasonal More pronounced in terrestrial ecosystems

Carbon stores 1023 grams of C = 100 million Gt (1 Gt = 109 tons) 55,000 Gt in C pool Oceans –38,000 Gt dead organic matter –1500 Gt living biomass – 750 Gt Terrestrial – dead organic matter – 1500 Gt living biomass – 560 Gt Atmosphere – 750 Gt

Carbon exchange Ocean exchange site — surface water Circulates via currents and movement through food chain Terrestrial exchange site – governed by photosynthesis / respiration Large stores in soil increases from tropics poleward

Nitrogen cycle Essential in proteins rubisco Usable forms = NH4+ and NO3- N stores in atmosphere = N2 N enters ecosystem through: wetfall/dryfall N fixation Cosmic radiation/lightening/meteor trails biologically— N fixing bacteria

Biological N fixation Provides 90% of available N to ecosystems Splits N2 into 2 N + H+  NH3 For each gram NH3 use 10 grams glucose Agents Legumes/symbiotic bacteria free-living aerobic/anaerobic bacteria—Azotobacter/Clostridium Cyanobacteria (blue-green algae)—Nostoc/Calothrix Lichens

N availability Ammonification –process of breaking down organic matter and producing NH3 Soils slightly acidic Quickly converts to NH4+ Nitrification –converting NH4+ to NO2- and then to NO3- Denitrification—reduction of NO3- to N2O and N2

N export & stores NO3- most common form exported High demand for N ecosystem and global cycling similar N stores Atmosphere –largest pool 3.9 X 1021 Biomass and soils – 3.5 X 1015 / 95-140 X 1015 Oceans—inputs from rivers and atmosphere 36 X 1012 / 30 X 1012 Biomass—15 X 1012 Denitrification returns 110 X 1012 to atmosphere

Phosphorus cycle No atmospheric input--follows hydrological cycle only Often in short supply Reservoirs – Rock + natural phosphate deposits Internal cycling important—3 states organic P, dissolved organic P & inorganic P Inorganic P taken up by primary producers eaten by zooplankton—excreted or retained P used by bacteria not recycled

P can be deposited into sediments Global cycling unique—no atmospheric inputs / river inputs important in oceans High turnover rate

Sulfur cycle Sedimentary and gaseous phases Carried in salt solutions tied up in deposits—released by weathering Atmospheric input—fossil fuels, volcanic eruption, ocean surface water, decomposition

Enters as H2S—oxidized to SO2 carried as H2SO4 –result = acid rain Important in amino acids Decomposition—released as HSO4- or SO42- Presence of Fe, S precipitates out as FeS2

Global cycling of S Least understood of nutrients Gas phase allows global cycling Inputs: Oceans contain large pools, but do not contribute much Input into atmosphere: Forest fires Volcanic Industrial

Oxygen cycle Complex cycle—linked to other nutrients Sources of O2 photosynthesis breakup of H2O in atmosphere Presently --balance of photosynthesis and respiration O2 produced as byproduct of anaerobic respiration O2 released by weathering of rocks O available in water and carbon dioxide

Redfield ratio Cycles of nutrients are linked Stoichiometry—quantitative relationships of elements in combination Redfield ratio—constant atomic ratio despite ambient nutrient concentrations C:N:P 106:16:1 106CO2 + 16NO3- + HPO42- + 122 H2O + 18H+ (CH2O)106(NH3)16(H3PO4) + 139 O2