USING END-MEMBER MIXING ANALYSIS TO UNDERSTAND STORM-EVENT STREAMFLOW IN LOWLAND WATERSHEDS OF COASTAL SOUTH CAROLINA
Watershed-80 (WS-80), in the US Forest Service’s Santee Experimental Forest near Charleston, SC, drains 200 hectares dominated by clayey soils. Upper Debidue Creek (UDC), near Clemson University’s Baruch Institute in Georgetown, SC, drains 162 hectares of mostly sandy soils. Samples from water-table wells, piezometers, lysimeters, and rain gauges at these two sites were analyzed for major cation and anion concentrations, and results were used to construct EMMA models for each site.
Preliminary findings suggested that deep groundwater was less susceptible to chemical fluctuation than shallow and riparian groundwaters, which are subject to effects from storm events and seasonal changes. Rainwater ion chemistry varied widely, in response to meteorological factors. These findings support the use of seasonal and/or event-specific tracer concentrations for end-member chemical characterization. The EMMA models will be used to compare groundwater and stream flow response to storm events at WS-80 and UDC. We hypothesize that the clayey soils at WS-80 will cause faster runoff response to storm events, as indicated by decreased groundwater and increased precipitation contributions to streamflow, than at UDC. In a time of rapid land-use change, this study contributes to a growing understanding of groundwater and surface-water interactions in minimally disturbed, forested, lowland watersheds.