chapter 22 biogeochemical cycling. the universe when? how? 15 x 10 9 years ago matter existed in its...
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Chapter 22Biogeochemical 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
Basic element of all organic compounds
Inseparable with energy flow
Source of CO2
atmosphere/water
Primary producers decomposers
Carbon
Net ecosystem productivityRate at which C is taken up in
photosynthesis and lost due to respiration.
Determined by Primary productionDecomposition
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 afternoonrespiration highest just before daylight
Seasonal variation—varies according to weathervaries with climatevaries 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 poolOceans –38,000 Gt
dead organic matter –1500 Gtliving biomass – 750 Gt
Terrestrial – dead organic matter – 1500 Gt living biomass – 560 GtAtmosphere – 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 cycleEssential 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 glucoseAgents
Legumes/symbiotic bacteriafree-living aerobic/anaerobic bacteria—Azotobacter/ClostridiumCyanobacteria (blue-green algae)—Nostoc/CalothrixLichens
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 Necosystem and global cycling similarN 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 supplyReservoirs – Rock + natural phosphate
depositsInternal cycling important—3 states
organic P, dissolved organic P & inorganic PInorganic P taken up by primary producers
eaten by zooplankton—excreted or retainedP used by bacteria not recycled
P can be deposited into sediments
Global cycling unique—no atmospheric inputs /
river inputs important in oceansHigh turnover rate
Sulfur cycle
Sedimentary and gaseous phasesCarried in salt solutions
tied up in deposits—released by weatheringAtmospheric input—fossil fuels, volcanic
eruption, ocean surface water, decomposition
Enters as H2S—oxidized to SO2 carried as H2SO4 –result = acid rainImportant in amino acids
Decomposition—released as HSO4- or SO4
2-
Presence of Fe, S precipitates out as FeS2
Global cycling of SLeast understood of nutrientsGas phase allows global cyclingInputs:Oceans contain large pools, but do not contribute much Input into atmosphere:Forest fires Volcanic Industrial
Oxygen cycleComplex cycle—linked to other nutrients
Sources of O2 photosynthesis
breakup of H2O in atmospherePresently --balance of
photosynthesis and respiration
O2 produced as byproduct of anaerobic respiration
O2 released by weathering of rocksO available in water and carbon dioxide
Redfield ratio
Cycles of nutrients are linkedStoichiometry—quantitative relationships of
elements in combinationRedfield ratio—constant atomic ratio despite
ambient nutrient concentrations C:N:P 106:16:1
106CO2 + 16NO3- + HPO4
2- + 122 H2O + 18H+ (CH2O)106(NH3)16(H3PO4) + 139 O2