ABSTRACT
Dissolved organic carbon (DOC) contributes to the acidity of water, the mobility and toxicity of metals and organic pollutants, and the availability of nutrients in soils and aquatic systems. At the global scale, DOC plays a role on the C cycle primarily through the very large amount stored in the oceans. In using the terms sources and sinks, it should be made clear that a sink for one system may be a source for another and that sinks may be of a temporary, transient nature, with much of the DOC produced ultimately being returned to the atmosphere as CO2. At the global scale, however, the importance of DOC fluxes is lost because there can be internal movement of DOC within systems, such as soils, without export. The chapter examines controls on DOC production and retention in soils and concludes with a discussion of the ways in which disturbance may affect the soil DOC budget and catchment export.
