Modeling Soil Solution, Mineral Formation and Weathering

Simulation models are valuable tools to increase understanding of complex soil chemical processes. Initially modeling was restricted by limited computational power; thus, complex natural systems were often simulated with site-specific, regression-based models. These models (classified as functional models by Hoosbeek & Bryant, 1992) do not deal with the actual processes but were designed to simulate the response of the studied system to specific variables. Although useful for the conditions represented by the collected data set, these models are usually not suited for other environments. Often the process controlling variables or responses to these variables are different in different environments. Nonetheless, due to the complexity of natural systems, quantitative mechanistic models often do not exist. The development of quantitative models has evolved from initial attempts to determine species distributions and ion activity, to models that attempt to represent chemical processes including soil mineral formation and prediction of soil solution composition and rates of mineral weathering. In this chapter we present an overview of the types of quantitative models suitable for describing soil chemical processes including mineral weathering. Generally following a chronological development, the models can be classified into a series of increasingly complex treatments of the natural system.