Biological and Geochemical processes

Biogeochemical cycles: nutrient cycles with both biotic and abiotic factors

The Nitrogen Cycle

In nitrogen fixation, microorganisms convert N₂ to ammonium (NH₄⁺) a more usable form of nitrogen because N₂, which is more abundant, is unusable by plants.

Nitrification: ammonium (NH₄⁺) is oxidized to nitrite (NO₂⁻) and then nitrate (NO₃⁻) by bacteria.

Denitrification: undoes nitrification so that bacteria can get the oxygen they need from nitrate rather than O₂

Ammonification: nitrogen is changed back to ammonium

Hydrologic Cycle: Water Cycle

Very little water is chemically hanged by biotic and abiotic factors. This cycle is more physical than chemical.  

Carbon Cycle

Photosynthesis and respiration cause most of the transformations of carbon. The return of CO₂ in the atmosphere by photosynthesis is balanced by its removal through respiration. Unfortunately, the burning of wood and fossil fuels upsets this balance, increasing the amount of atmospheric carbon dioxide.

Phosphorus Cycle

Phosphorus is not significantly present in atmospheric gases, so it tends to cycle over a small area. Weathering of rocks adds phosphate into the atmosphere. Plants use phosphate, an organic form of phosphorus, for organic synthesis. It is then transferesd to consumers and added to the soil by decomposers.