Dissolved Humus in Soil Waters

Humus is defined as being synonymous with soil organic matter, which in turn is the total organic matter in a soil exclusive of the biomass and undecayed material. Dissolved humus consists of the dissolved organic material (DOM) in soil, which influences the overall ecology and geochemistry of soil. This chapter focuses on the DOM's ecological role in the unsaturated zone, with the saturated zone and the surface aquatic ecosystems being peripherally considered. The relation of the DOM to other ecological components in soil is influenced by two types of fluxes. The first one is physical diffusion. The DOM diffuses over a concentration gradient. The second physical flux is convection, which is dependent on a gradient in the soil's water content as a result of precipitation. The dissolved humus is mobile and so it can be fully available theoretically. This mobility and availability is not constant; it can vary both over space and time. The potential ecological function and in situ availability of the dissolved humus are considered in the chapter so that one is able to understand and predict its environmental role.