MEASURING SEASONAL STREAM SALINITY IN EASTERN NEBRASKA'S ROCK CREEK TO AID TIGER BEETLE PRESERVATION

The saline wetlands in Lancaster County, NE are a unique ecosystem that provide habitat for the endangered Salt Creek Tiger Beetle (Cicindela nevadica lincolniana). Current populations numbering only in the hundreds, utilize the saline soils along banks and on channel bars within several creeks in the area for mating, oviposition, and larval burrowing. Efforts are currently underway to better characterize beetle habitat in order to preserve existing populations and to aid reintroduction of the species. The dissolved salts found in the region's streams are believed to originate from saline groundwater discharge to the streams from within the underlying Dakota aquifer. One of these streams, Rock Creek, flows through northeastern Lancaster County and traverses saline wetland areas before flowing into the larger Salt Creek. To better constrain seasonal variations in stream water chemistry and its potential impact on tiger beetle behavior, this study monitored stream temperature, specific conductance and salinity in the Rock Creek watershed as part of a larger ongoing stream water quality monitoring study. Weekly measurements were taken on approximately the same day and at the same time at three specific sites along the water course. Three readings were taken at each site and averaged to get the final recorded reading. Preliminary findings showed that the specific conductance and salinity of the stream varied following rainfall events, but overall were fairly constant at each site. The site farthest upstream, along US Highway 77, had the lowest specific conductance (typically ranging from 0.668 to 0.716 mS/cm) and thus lowest salinity (between 0.2 and 0.4 ppt) of the three sites measured. The middle site at Rock Creek Road had the highest specific conductance typically ranging between 0.771 and 1.165 mS/cm. The site farthest downstream, on Greenwood Road, typically had specific conductance values ranging from 0.734 and 1.051 mS/cm. The salinity of the two downstream sites ranged from 0.3 to 0.6 ppt. Determining variations in the specific conductance and salinity within Rock Creek, and the other streams flowing through the saline wetlands will lead to better understanding of the Salt Creek Tiger Beetle's habitat requirements and improve its chances for survival.