Specific conductance–stage relationships in Appalachian valley fill streams

Surface coal mining impacts on water resources in the Appalachian region, USA, are widely studied. Total dissolved solids (TDS), which are estimated in situ by the proxy variable specific conductance (SC), are of interest due to potential aquatic macroinvertebrate effects. Prior studies have documented the hydrochemical impacts of surface mining on streams, but research on the relationships between SC and discharge is limited. SC–Stage relationships can help infer potential hydrologic flow paths, as well as source water TDS concentrations in mining-influenced watersheds. The objectives of this study were to compare baseflow and stormflow hydrochemistry and determine SC–Stage relationships in valley fill (VF) streams. Five VF streams of varying ages in Virginia were equipped with continuous SC and stage data loggers for up to 12 months (December 2013–November 2014). Data analyses included baseflow and stormflow hydrochemistry, and SC–Stage regressions and storm hysteresis patterns. Data were analyzed seasonally. Stages were generally highest in winter and lowest in summer, while SCs were generally highest in summer and lowest in winter. All SC–Stage regressions indicated SC dilution during stormflow, but significance differed seasonally. Storm SC–Stage hysteresis patterns varied with storm precipitation amounts, season, and vegetative period, implying climatic controls on VF stream storm responses. Counterclockwise storm hysteresis likely occurred in response to high rainfall amounts exceeding the mine soil infiltration capacity. Clockwise storm hysteresis likely resulted from precipitation dissolving salts brought to the surface by evapotranspiration, but may have also resulted from rapid flow through pseudokarst features within the VF.