Anion mobility in soils: Relevance to nutrient transport from forest ecosystems

Abstract

Nutrient transport from forest ecosystems is strongly regulated by the availability of anions in soil solution. Each of the major anions in forest soil solutions has some unique properties which affect its production and mobility. The production of bicarbonate, one of the most common anions, is regulated by soil CO 2 pressure and pH. The mobility of phosphate is most strongly affected by adsorption reactions. The mobility of nitrate is regulated almost solely by biological processes, whereas chloride is relatively uninvolved in either biological or inorganic chemical reactions. Sulfate is intermediate, being involved in both biological and inorganic chemical reactions. Knowing these properties of the major anions, it is possible to assess and to predict the effects of several diverse site manipulations on soil leaching rates. Case studies from a site in Washington State consistently demonstrate the importance of accounting for bicarbonate transformations following site manipulations. Although organic anions are frequently dominant in cold-region soil solutions, very little information on the complex factors affecting their mobilities is available. Further research into organic anion mobility and futher attention to bicarbonate mobility should add greatly to the body of knowledge on nutrient transport processes in forest soils.