Developing and adapting soil process submodels for use in the pedodynamic orthod model.

This chapter examines the development and structure of the ORTHOD computer model which simulates soil forming processes involved in the formation of a Typic Haplorthod. It presents newly developed and adapted soil process sub models used as building blocks in an integrated pedodynamic model. The LEACHM model uses a numerical solution to the convection-dispersion equation to estimate chemical fluxes. Solute movement consists of three components: convective, diffusive, and dispersive transport. The soil temperature and volumetric water content data used as input to the microbial decomposition submodel were derived from the output of the soil temperature and water movement submodels. Ion exchange was recognized as an important process controlling the chemistry of the soil solution. Since the objective of the pedodynamic model is to simulate the chemistry and movement of the major chemical components, a chemical speciation and precipitation submodel was needed.