General concepts of nutrient flux and stability

Abstract

Water can carry a wide array of dissolved substances, including every bioelement [human urine, for example, contains up to 80 dissolved compounds (Botkin, 1990)]. Thus the fluxes of many important nutrients are closely connected with the hydrological cycle, nutrients with gaseous forms such as N₂ and CO₂ being partial exceptions. The concentration of any given dissolved substance in the waters on the earth’s surface is variable, both in space and time. The dissolved substances in a particular unit volume of water depend on the recent history of that water. Passage of water through rocks and soil dissolves chemical compounds, whole processes such as diffusion, the mixing of water from different sources, and evaporation causes changes in concentrations. These processes go on even in the absence of biota, and it will be useful to begin the mathematical description of these nutrient dynamics in physical systems without the complication of biota.