ABSTRACT
Soil water, or the aqueous phase, is arguably the most important phase in the soil. Almost all chemical reactions in soil are mediated by or occur in the soil solution. Some of the more important types of chemical reactions that occur in soil water, affecting the fate and behavior of substances in the environment, are: hydration-hydrolysis, acid-base, oxidation-reduction, and complexation. The soil solution mediates many of the reactions that control the retention of substances by soil solids, such as precipitation-dissolution, adsorption-desorption, and ion exchange. The extent to which these retention-controlling reactions occur is dictated by substance behavior in soil water. The soil solution is also the principal phase in which substances move in and through the soil. It is for these reasons that considerable emphasis is placed on understanding the processes that occur in the soil solution, as well as the ability to predict how these processes will impact substance fate and behavior.
