Equilibrium is necessary in the various bio-geo-chemical cycles.
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Along with energy, water and several other chemical elements cycle through ecosystems and influence the rates at which organisms grow and reproduce. ... The most important biogeochemical cycles affecting ecosystem health are the water, carbon, nitrogen, and phosphorus cycles.
A biogeochemical cycle or inorganic-organic cycle is a circulating or repeatable pathway by which either a chemical element or a molecule moves through both biotic ("bio-") and abiotic ("geo-") compartments of an ecosystem. In effect, an element is chemically recycled, although in some cycles there may be places (called "sinks") where the element accumulates and is held for a long period of time. In considering a specific biogeochemical cycle, we focus on a particular element and how that element participates in chemical reactions, moving between various molecular configurations. Of the 90-odd elements known to occur in nature, some 30 or 40 are thought to be required by living organisms (Odum, 1959). We will be considering only a few of these, mainly those utilized in fairly large quantities by living organisms. The principal elements of life are carbon, hydrogen, oxygen, and nitrogen. However, a number of others are certainly important to understand as well, notably phosphorus and sulfur. Some "non-essential" elements participate in biogeochemical cycles, entering organism tissues because of chemical similarity to essential elements. For example, strontium can behave like calcium in the body.