USING SURFACE AND GROUND WATER CHEMISTRY TO INVESTIGATE SPATIAL VARIATIONS IN STREAMWATER CHEMISTRY AND THEIR POSSIBLE CONNECTION TO PREVIOUS LAND USE IN A HEADWATER STREAM

Determining controls on stream water chemistry is vital to developing a better understanding of runoff generation and improving management plans in first- and second-order watersheds. In order to investigate these controls, we investigated where connections between groundwater and stream water occurred during baseflow in the 43 ha Gribble Gap watershed located in Cullowhee, NC. Seven focus sites were selected in the watershed, each with a stream water sample point and a groundwater well on either side of the stream. We took 3 baseflow samples over the course of 3 weeks, which were analyzed for a variety of constituents, and measured hydraulic head in relation to the height of stream water. Additionally, topographic metrics for each sub-watershed were compared to patterns in stream water chemistry. We found that groundwater and stream water chemistry were variable throughout the watershed at baseflow, and that each tributary had its own unique chemical signature. The high variability in groundwater concentrations suggested that groundwater could not be used as an end-member to describe spatial patterns in runoff generation, and the unique concentrations at each stream head were likely indicators of either lithologic changes or variations in the length of flow paths, potentially from the affects of past land use. The hydraulic head data indicated that the stream was losing in some reaches and gaining in others. These data indicate there is a complex and dynamic interplay between groundwater and surface water, even during baseflow in a small headwater catchment. Finally, topographic analyses suggests some of the variability in stream water chemistry may be explained by landscape changes driven by past land-use. These findings may help us better understand baseflow and runoff generation and aid in watershed management in similar settings.