BIOGEOCHEMICAL CYCLING

The flow of chemical substances to and from the major environmental reservoirs: Atmosphere, Hydrosphere, Lithosphere, and Biosphere. As chemicals move in the cycle, they often change chemical form, usually existing in a characteristic form in each reservoir. As an example, carbon (in the lithosphere) exists mainly as carbon dioxide in the atmosphere, carbonic acid, bicarbonate, or the carbonate ion when dissolved in water (hydrosphere), and as more complex organic compounds in animals and plants (biosphere).