1. Biogeochemical Cycles
Vivek Srivasatava

2. Energy/Matter Flow
• Energy and matter flow through the
biosphere
• Sun >> autotroph >> heterotroph >> fossil
fuel storage >> human fuel consumption
• Biosphere < > lithosphere < > atmosphere
< > hydrosphere
• Elements cycle through both the biological
and geological world, hence
biogeochemical cycles

3. Elemental Cycles
• H, O, and C make up > 99 % of the Earth’s
biomass
• N, Ca, K, Mg, S, and P are significant
nutrients
• Cycling of C, O, N, P, and S are discussed
in this chapter

4. Concepts in Biogeo. Cycles
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Reservoir - where material or mass is stored
Flux: rate of flow of material
Steady state: inflow = outflow
Dynamic state: fluxes are reservoirs are
changing with time
• Residence time: length of time a chemical
stays in a reservoir
• Feedback: positive and negative

5. Reservoirs of Carbon
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Carbon is found in all four spheres
Biosphere - organic matter
Atmosphere - CO2, CH4
Hydrosphere - H2CO3 ,HCO3 - , CO3 =
Lithosphere - CaCO3 , coal, oil, and gas
Processes: photosynthesis, formation of
sediments, weathering, combustion, plate
tectonics

6. Carbon Cycle

7. Human Interference
• Human-induced processes
– Extraction and combustion of fossil fuels
(speeds up the medium-term cycling)
– Cement manufacturing
– Deforestation (biomass burning)
• All of these processes release CO2 into the
atmosphere and affect the natural cycling of
carbon

8. Oxygen Cycle
• Essential for aerobic life
• Closely linked to carbon cycle
• Very large reservoir (20% of gas in atm.),
not susceptible to human interference
• Also, not a greenhouse gas
• Reservoirs: atmosphere, surface organic
material (biosphere), and buried organic
matter (lithosphere)

9. Nitrogen Cycle
• Essential to life - important in forming
amino acids >> proteins
• Most abundant in the atmosphere (79%)
• Flows continuously through the spheres
• Reservoirs: atmosphere and biosphere (soil)
• Processes: Nitrogen fixation/ nitrification
and denitrification
• Atmosphere => soil => plants =>
atmosphere (fig. 5.7)

10. Nitrogen Cycle
• Nitrification/ nitrogen fixation: converts N 2
to forms usable by plants (NH3, and NO3-)
• Denitrification: is the conversion of NO 3back to N2 in the atmosphere or in gases in
the soil
• Symbiotic relationship: bacteria supply the
plant with usable nitrogen and feed off the
sugars and starches made by the plant

11. Nitrogen Cycle
• Human activities account for >50% of
nitrogen fixation (fertilizers, cultivation of
nitrogen fixing plants)
• Denitrification - done mainly by bacteria
not by humans.
• Despite the huge size of the atmospheric
reservoir of nitrogen, human activites
profoundly affect the nitrogen cycle

12. Nitrogen
Cycle

13. Eutrophication
• Consequence of excess nutrients (nitrates,
phosphates) entering bodies of water
• Produces algal blooms (over productivity)
• When these algae die they settle at the bottom of
the water column
• Decomposition process consumes oxygen and
depletes it from water
• This destroys the organisms that need oxygen
(fish)- Lions Lake, Warrensburg, source of
nutrient - goose droppings

14. Phosphorus Cycle
(Phosphorus is required for the manufacture
of ATP and all nucleic acids)
1. Reservoir – erosion transfers phosphorus to water and
soil; sediments and rocks that accumulate on
ocean floors return to the surface as a result of
uplifting by geological processes
2. Assimilation – plants absorb inorganic PO43(phosphate) from soils; animals obtain organic
phosphorus when they plants and other
animals
3. Release – plants and animals release phosphorus when
they decompose; animals excrete phosphorus
in their waste products

15. Phosphorus Cycle
• Long-term cycle: Burial of phosphate in
sediments => uplift => weathering =>
phosphate in soil or ocean
• Residence time ~108 yrs
• Extraction (mining) short-circuits the longterm cycle

16. Phosphorus Cycle
• Reservoirs: Hydrosphere (as phosphate
ion), lithosphere (phosphate minerals), and
biosphere (bones, teeth, shells)
• Short-term cycle: PO43- in soil or ocean =>
assimilation by plants => consumption by
animals => decay or excretion => recycled
to soil or ocean, residence time 100s of yrs

17. Phosphorus Cycle
• Atmosphere is not a source
• As with nitrate, phosphate is an important
nutrient in coastal upwelling zones
• As with nitrate, humans are doubling the
rate of transport of phosphate into the
environment through the application of
fertilizers

18. Nitrogen Cycle

19. Phosphorus Cycle