MONITORING SEASONAL STREAM SALINITY IN EASTERN NEBRASKA'S LITTLE SALT CREEK TO ASSIST TIGER BEETLE PRESERVATION

The streams running through, or near the saline wetlands of eastern Nebraska, north of Lincoln, as well as the wetlands themselves are home to the endangered Salt Creek tiger beetle (Cicindela nevadica lincolniana). Adult beetles use the saline stream banks and sand bars for mating and egg laying. Larva feed on passing prey from within burrows excavated into the saline soils. Reintroduction and repopulation efforts are ongoing, but to achieve success, wetland managers need information on the source of the salinity, and about the mixing dynamics of various water inputs to the stream. To that end, this study monitored seasonal variations in stream water quality along one stream reach as part of a larger ongoing stream water quality monitoring program across the region. Little Salt Creek, classified as a second order stream, has a reach length of approximately 21 kilometers from north to south before emptying into Salt Creek. Seven sampling locations have been established along the creek. At each location temperature, electrical conductivity, and salinity measurements have been taken weekly using a YSI 30M probe. Preliminary results indicate that Little Salt Creek's salinity increases as the water moves downstream. Salinities ranged from as low as 0.2 ppt at the headwaters to as high as 8.4 ppt near the confluence with Salt Creek. The salinity source is most likely saline groundwater seepage to the stream upwelling from the underlying Dakota aquifer. Overland flow is another possible source; however, given the surrounding landscape's flatter topography, and soil structure, it is likely a small factor. The highest electrical conductivity recorded was 16.56 mS/cm near the confluence, with a low of 0.407 mS/cm slightly downstream of the headwaters. Temperatures varied between 20° and 30°C during the data gathering period. These temperatures reflect seasonal weather variations and varied hydrologic inputs to the stream. Research on the groundwater flow dynamics in and out of the stream along with chemical analyses will give a better understanding of the sources of salinity. The data collected in this study will assist wetland managers by providing insight on the seasonal and spatial variations in stream salinity.