Biogeochemical cycles

Absorption by roots (P)

plant roots absorb the phosphates that they will use in metabolic processes. Plants have symbiotic relationships with mycorrhizal fungi. These have extensive networks of fungal hyphae in the soil which increases the surface area for phosphate absorption

Decomposition (P)

the breakdown of phosphorylated proteins in dead organic matter releases phosphates that are often made more soluble by soil microbes so they can be absorbed by plants

Sedimentation (P)

the phosphorous in organisms that die and become incorporated into sediments may no longer be available to other organisms. This reduces the productivity of the surface waters of oceans because phosphorous availability is often a limiting factor

Mountain building/weathering (P)

processes that mobilise phosphorous and make it available to living organisms are often slow. The phosphorous in marine sediments may not become available again until continental drift forms new mountain ranges and weathering of rocks releases phosphates

Mining of phosphate rocks

most phosphorous is mined as calcium phosphate then treated to produce ammonium phosphate which is more soluble. Example is bird droppings forming deposits of guano which have nearly all been fully exploited in areas such as Peru

Fertiliser use (P)

the use of fertilisers mobilises phosphorous compounds into the environment in more soluble forms. This increases crop production but can also contribute to eutrophication

Sustainable management of the P cycle

• large areas of farmland experience shortage of phosphates due to the removal of biomass and the loss of phosphates by soil erosion. Maintaining future supplies of phosphates to compensate for these losses by mining rock phosphates is unsustainable

• Biological wastes used as fertilisers to maintain P nutrient availability

• Crop breeding programmes are increasing the efficiency of P absorption by crops

In what forms does C exist in the atmosphere

CO2, CH4, CO

In what forms does C exist in the hydrosphere

hydrogen carbonate ions, dissolved CO2

In what forms does C exist in the biosphere

carbohydrates, proteins, lipids

In what forms does C exist in the lithosphere

carbonaceous rocks and fossil fuels

Fossilisation (C)

The incomplete decomposition of dead organic matter, often under anaerobic conditions, can produce substances that form long-term carbon stores such as fossil fuels. Some organisms such as molluscs, corals and many planktonic organisms produce exoskeletons that include calcium carbonate. This may produce rocks such as limestone, which now contain most of the carbon in the lithosphere

Changes in photosynthesis affect on C cycle

• deforestation reduces movement of C from atmosphere into biomass

• marine pollution reduces the absorption of CO2 as phytoplankton die, so more CO2 from the atmosphere dissolves in the ocean to maintain equilibrium

Changes in aerobic respiration affect on C cycle

Ploughing increases O2 supply to decomposers so aerobic decomposition occurs more rapidly, more carbon released into atmosphere and removed from the dead organic matter

Changes in anaerobic respiration affect on C cycle

Anaerobic environments produced by humans that produce methane gas:

• rice padi fields

• landfill sites

• anaerobic sediments in reservoirs

• livestock intestines

Anaerobic environments destroyed by drainage:

• waterlogged fields

• marshlands

• peat bogs

Changes in carbonic acid conc in the sea affect on C cycle

Humans indirectly cause increased carbonic acid as anthropogenic activities increase CO2 which causes more to dissolve into oceans and decrease the pH.

Changes in methane released from fossil fuels affect on C cycle

methane may be released into the atmosphere during fossil fuel extraction

Changes in combustion affect on C cycle

the combustion of fossil fuels and wood releases large amounts of CO2 into the atmosphere

Changes in biomass movements affect on C cycle

Human activities can produce local changes that have environmental impacts:

• addition of compost/mulch to improve soil fertility

• deforestation + crop harvesting leads to reduced soil organic matter + more soil erosion

• movement of marine biomass into terrestrial system by fishing/aquaculture