NEBRASKA'S EASTERN SALINE WETLAND HYDROLOGY: CLARIFYING THE GROUNDWATER CONNECTION

Public agencies are actively working to protect, rehabilitate, and understand the endangered saline wetland ecosystems of eastern Nebraska. Originally encompassing approximately 8100 hectares, only 1600 hectares remain of the saline wetlands. These wetlands are home to a federally endangered insect and a variety of rare, salt tolerant Nebraska plants. Two publicly owned saline wetland sites are the Little Salt Creek Wildlife Management Area and the Frank Shoemaker Marsh Wetland Complex, both located in northern Lancaster County, Nebraska. The source of saline water to the wetlands is deemed to be from groundwater inflow from deeper in the underlying Dakota Formation. The Dakota Formation is composed of Cretaceous-age sedimentary rocks including sand, silt and clay units. This study installed four wells at the two sites to monitor long-term changes in water level and water chemistry. Preliminary water level measurements detected the water table at approximately 3.7 meters below the surface at the Frank Shoemaker Marsh inferring no direct groundwater to surface connection for saline water. Comparatively at the Little Salt Creek site, one study well flows at the surface, clearly indicating a groundwater surface connection. The disparity in water levels between sites despite similar saline wetland surface expressions motivates further groundwater flow chemistry analysis to determine surface connection of saline groundwater. Initial water quality measurement at the Little Salt Creek flowing well yielded a water specific conductance of 22.15 mS/cm compared to 14.79 mS/cm at a well adjacent to the channel with a water table level of 3.7 meters below the ground surface. In contrast, the well adjacent to Little Salt Creek at Frank Shoemaker Marsh had a higher specific conductance of 34.05 mS/cm compared to a specific conductance of 9.78 mS/cm for a well set 91 meters from the channel. Creek channelization, streambed degradation, and head-cutting on surface seeps and saline wetlands play a significant role in the loss of the unique saline wetlands. In addition, continued threats from agriculture and urban development warrant a further understanding of the hydrological functions of the saline wetlands for future protection and rehabilitation of the remaining unique ecosystems.