ABSTRACT
Mass balance simply means a budget. In the context of catchment studies, it is a budget that describes fluxes of solutes into and out of a catchment, and assigns the solutes to specific sources and sinks such as atmospheric deposition, biomass change, or bedrock weathering. Soils contain exchangeable cations and anions that are in equilibrium with the soil solution. As the composition of the soil solution changes, ions will be exchanged between the solid phase and solution. If the soil solution composition does not change with time, adsorbed ions will not change either and ion exchange will make no contribution to the solute budget. There is no simple direct way of measuring the contribution of chemical weathering to the solutes measured at the output of a catchment.
