WORTH ITS SALT: THE ROLE OF SHALLOW GROUNDWATER IN EASTERN NEBRASKA'S SALINE WETLANDS

Eastern Nebraska's saline wetlands are a unique, but critically imperiled ecosystem. These saline wetlands are sustained by complex interactions between surface water and groundwater. Understanding these interactions is crucial to the preservation of threatened animal and plant species, specifically the federally-endangered Salt Creek tiger beetle and state-endangered salt wort. A site on the north edge of Lincoln, NE was chosen to investigate the physical and chemical characteristics of groundwater beneath a typical saline wetland area. The site is located along the lower reaches of Little Salt Creek, near its confluence with Salt Creek. The site's geology consists of Quaternary alluvium overlying Cretaceous-age Dakota sandstone. Alluvium thickness varies between 7.6-24 meters across the site. Four monitoring wells were installed on both sides of the stream in lines perpendicular to the channel to characterize lateral groundwater flow across the floodplain. A monitoring well was also installed on each side of the creek, separate from the transect line of monitoring wells, to determine the water table position and groundwater flow direction within the study area. All wells were screened in a sand layer within the alluvium at depths of 6 to 9 meters. Initial water level measurements indicated that the water table in the floodplain exists between 3.6-4.6 meters below surface. Initial specific conductance (temperature-corrected to 25°C) and salinity measurements showed a wide range of values across the site. Specific conductance values ranged from 0.9 mS/cm to 28.43 mS/cm. Salinity values varied similarly, with a range of 0.4 to 17.6 ppt. The investigation at this site was also augmented by observation at the remnants of an old railroad trestle whose support posts were cut off near the ground surface. The posts are encrusted with salt and presumably provide a conduit for shallow (about 3 meters below surface) saline water to reach the surface. Water bubbling to the surface adjacent to one of these posts had a specific conductance of 22.0 mS/cm. The understanding gained from long-term monitoring of water levels and chemistry will aid the City of Lincoln, the local Natural Resource Districts, and other involved agencies in the management and conservation of these endangered saline wetlands.