DETERMINING THE HYPORHEIC INTERFACE AND SCALE OF ECOLOGICAL SIGNIFICANCE IN THREE WESTERN NEW YORK STREAMS

Hyporheic activity in Western New York streams is poorly studied and may play an important ecological role in governing water quality. Three streams in the Cattaraugus Creek Watershed were studied at reach scale to determine the extent and significance of groundwater surface water interactions. Due to the glacial history of the watershed, it is extremely physically heterogeneous, but chemically homogenous. This is a result of varying depositional facies with similar source materials. Thus, over the entire watershed, chemical variation from groundwater surface water interaction should be dependent upon physical heterogeneity and biological activity. Highly impermeable till and lacustrine clays inhibit flow so that ecological hot zones in the stream bed can only occur in specific places within the watershed, such as more permeable gravel deltas and glaciofluvial sediments that streams now cut through. These areas are of particular interest for ecosystem restoration, as these geologically controlled zones of enhanced cycling will require special attention. Distributed temperature sensing (DTS) and stream gaging were used to guide reach scale chemical and hydrologic sampling. These tools were seen to average hyporheic potential over a reach, as heterogeneities and smaller scale relationships appear to dominate the groundwater surface water interaction in these streambeds. This suggests a smaller scale of consideration. Head difference, nitrate, dissolved organic carbon (DOC), dissolved oxygen (DO%), conductivity, pH, and temperature data were gathered from minipiezomenter transects over a four-month period (summer to fall transition). With these data, signatures of groundwater and surface water mixing were determined to constrain a conceptual model for hyporheic activity in the watershed. Streambed topography appears to play its theoretical role regarding hyporheic flow, but spatial heterogeneity further constrains the interface of mixing within a single watershed such that it limits ecological factors. Deep groundwater upwelling from the watershed scale appears to play a variable role in these parts of the watershed as noted from stratified chemistry.