The Aquatic Interface

Abstract

Soil-mediated effects are an important factor in determining the chemistry of surface waters even though (1) some waters do not intimately contact soil before entering lakes and streams and (2) soil-contacted waters often are further modified by contact with rocks and minerals after leaving soils and before being discharged to surface waters. The nature of soil-mediated effects is often not well understood. Some workers have been skeptical that acid deposition could cause significant acidification of surface waters that come into contact with soils because of the large buffering capacity inherent in soils through such processes as cation exchange, mineral dissolution, and protonation of organic acids (Krug and Frink 1983). Others have assumed that the combination of documented increases in acidity along with high SO ²⁻₄ concentrations in areas of heavy acid deposition loading were sufficient a priori evidence to implicate acid deposition as the major causative agent (Schindler 1980; Schofield 1980). The resultant controversy has been enormous, as might be expected when apparently conflicting evidence is available on an issue that bears on regulatory policies that, in turn, could cost huge sums for compliance. It is unrealistic to expect that we can currently contribute sufficient insight into the relevant processes to resolve such a conflict. However, given our current level of understanding, perhaps this chapter can help to focus efforts on those processes that have a valid theoretical basis and, thus, help toward arriving at a rational resolution of the conflict.