Causes of concentration/discharge hysteresis and its potential as a tool for analysis of episode hydrochemistry

Episodic variations in dissolved solutes are frequently complicated by a cyclical relationship between concentration and stream discharge. Established three‐component models of runoff generation are used to explain this hysteresis effect and to illustrate how different component concentrations produce different hysteresis forms. It is demonstrated that a two‐component model cannot reproduce all the hysteresis forms commonly observed. A method, based on the three‐component system, is derived by which C/Q hysteresis can be used to predict relative component concentrations. This may provide a qualitative chemical description of sources supplying runoff for locations where these have not yet been directly established or a validation test where possible components have been sampled. The method has been tested using data collected at streams in the Adirondacks, New York, and the Northern Appalachian Plateau, Pennsylvania, during the Episodic Response Project of the U.S. Environmental Protection Agency. Predicted component compositions were in good agreement with measurements made during other studies and with those subsequently obtained from one of the Pennsylvania watersheds.