1. Chapter 22 Biogeochemical cycling

2. 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

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

4. 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

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

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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 / 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

15. 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

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

17. 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

18. 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

19. 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

20. 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

21. 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 :16:1
106CO2 + 16NO3- + HPO H2O + 18H+
(CH2O)106(NH3)16(H3PO4) O2