This document discusses several biogeochemical cycles, including the carbon, oxygen, nitrogen, and phosphorus cycles. It explains that carbon, oxygen, hydrogen, and nitrogen make up over 99% of the Earth's biomass and cycles these and other elements through the biosphere, lithosphere, atmosphere, and hydrosphere. The key concepts of reservoirs, fluxes, residence times, and feedbacks are introduced. Human impacts like fossil fuel combustion and deforestation are noted to affect the natural carbon cycle. The nitrogen cycle is profoundly impacted by human fertilizer use and cultivation, while phosphorus cycling is accelerated by phosphate mining and fertilizer application.

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