biogeochemical cycle
biogeochemical cycle The movement of chemical elements from organism to physical environment to organism in a more or less circular pathway. They are termed ‘nutrient cycles’ if the elements concerned are essential to life. The form and quantity of an element varies through the cycle, with amounts in the inorganic reservoir pools usually greater than those in the active pools. Exchange between the system components is achieved by physical processes (e.g. weathering) and/or biological processes (e.g. protein synthesis and decomposition). The latter form the vital negative-feedback mechanisms that regulate the cycles. Cycles may be described as varying from perfect to imperfect. A perfect cycle (e.g. the nitrogen cycle) has a readily accessible abiotic, usually gaseous, reservoir and many negative-feedback controls. By contrast, the phosphorus cycle, which has a sedimentary reservoir accessed only by slow-moving physical processes, has few biological feedback mechanisms. Human activities can disrupt these cycles, leading to pollution. Theoretically, perfect cycles are more resilient than imperfect cycles.
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biogeochemical cycle