Not only does climate variation modulate the vegetative cover and the soil properties that dictate the efficiency of the transformation of precipitation into runoff, but, at least as importantly, it can alter the timing, magnitude and even phase of the water inputs to the landscape. Runoff generated from snowmelt rather than rain events allows prolonged and higher peak discharges of water in rivers, with attendant impacts on sediment transport and river regime, and to the sedimentary record in estuaries. This falls under the umbrella of runoff generation mechanisms, which require attention to the physics of water flowpaths in the shallow subsurface. Knowledge of such systems is a necessary prerequisite for the study of the chemical fate of precipitation as it is transformed into runoff.
Rivers also carry solutes.
These are ultimately derived from the weathering of minerals in soils on the hillslopes in the catchment. A person studying such systems would need to be facile with low temperature aqueous geochemistry, soil physics, and runoff generation mechanisms.