The concept of biogeochemical cycles provides the framework for this project. It is a concept that recognizes the dynamism of multiple, complex processes that move, transform and store chemicals in the geosphere, atmosphere, hydrosphere, and biosphere. The term biogeochemical cycles expresses the interactions among the organic (bio-) and inorganic (geo-) worlds, and focuses on the chemistry (chemical-), and movement (cycles) of chemical elements and compounds. In its simplest form, cycling describes the movement of elements through various media and their return to their original state. Applying the concept of biogeochemical cycles provides a framework to identify and evaluate the sources and fates of chemical elements in a systems approach.
Separate biogeochemical cycles can be identified for each chemical element, such as the nitrogen (N), phosphorous (P), and carbon (C) cycles. However, through chemical transformations, elements combine to form compounds, and the biogeochemical cycle of each element must also be considered in relation to the biogeochemical cycles of other elements.
Elements and compounds also exist in the gaseous, solid, and liquid phases and can be transformed from one phase to another. In studying biogeochemical cycles, it is important to express in a common unit the amount of each element in all its phases and all its chemical compounds. This allows for establishing an "accounting system" for each element and for consideration of the conservation of mass. The principle of conservation of mass assumes that elements are neither created nor destroyed in the system. This assumption allows for conducting mass balance studies. Mass balance studies track all chemical forms and physical phases of an element, accounting for storage, transport, and transformation of the element.
Elements and compounds are stored in major reservoirs - the atmosphere, hydrosphere,
geosphere, and biosphere. The reservoirs are also interconnected, such that the output from one
reservoir can become the input to another. Movements of elements and compounds within each
reservoir and among reservoirs are called fluxes. Thus, interactions among the atmosphere, surface
waters, ground waters, soils, plants, trees, and sediments must be considered in biogeochemical
cycles. Water (H2O) is an important medium for transporting and transforming chemicals and the
hydrologic cycle is an important factor in biogeochemical cycles.
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