The chemical environment

Abstract

The chemistry of natural waters has been reviewed in a number of major texts (Hutchinson, 1957b; Davis and DeWiest, 1966; American Chemical Society, 1971; Allen and Kramer, 1972; Broecker, 1974; Holland, 1978; Stumm and Morgan, 1981; Drever, 1982) and the reader is referred to such texts for the complete treatment of the topics to be outlined here. There has been much emphasis of late on the global biogeochemical cycles of nutrients and other elements and the influence of human interference on such cycles (Woodwell and Pecan, 1973; Stumm, 1977; Trudinger and Swaine, 1979). Events in natural waters must be seen as part of a much larger, global picture. The ionic composition of natural waters is as much a function of the solution chemistry of the lithosphere as it is a function of chemical equilibria in situ. The ionic composition of the oceans may be thought of as resulting from a massive titration, with the acids provided by gases from volcanic activity and the bases provided by the rocks (Stumm and Morgan, 1981). Similarly the ionic composition of lakes results from the dissolution of rocks and other materials in the basin. In this case the dominant mechanism of chemical weathering is carbon dioxide dissolved in the groundwater. The quality of water in a lake is therefore heavily influenced by events in the drainage basin and must be seen in the light of soil type, land use and agricultural practice in that basin. In all that follows I will concentrate on events in surface waters where the phytoplankton grow. The distribution of nutrients in surface waters is, however, very much influenced by regeneration in deep water and events at the sediment interface and, where pertinent, such events will be discussed here. The reader is referred to the texts listed above for details of the full cycles of elements within lake and ocean basins.