"GROUNDWATER DYNAMICS WITHIN THE SALINE WETLAND ALLUVIUM OF THE LITTLE SALT CREEK VALLEY, LANCASTER COUNTY, NEBRASKA" Gordon Richard Coke; Advisor: Dr. Ed Harvey The eastern saline wetlands of Nebraska are the state’s most endangered ecosystem. They are the product of a unique mixing relationship between deep saline groundwater and fresh surface water runoff in floodplain depressions and swales, and stream channels in the Salt Creek basin. These wetlands are home to a variety of unique salt-tolerant plants such as salt wort (Salicornia rubra), sea blite (Suaeda depressa), and inland salt grass (Distichlis spicata), and the federally endangered Salt Creek tiger beetle (Cicindela nevadica lincolniana). The wetlands have diminished considerably in size over the past century due to development and drainage and their future is in jeopardy. To further understand the mixing dynamics that occur to sustain these wetlands, a large saline wetland hydrology study was initiated in the spring of 2007. This study examined the shallow hydrology and the impact of that hydrology on the endemic species within the wetlands. Specifically, an investigation into the groundwater dynamics of the alluvium was conducted to determine sedimentary layer salt content, transport pathways and groundwater levels. By expanding present knowledge about the saline wetland ecosystem, wetland managers will be equipped with better science to develop further management tactics for the protection and restoration of saline wetlands. The channelization of Salt Creek and subsequent streambed incision of its tributaries caused considerable groundwater drainage of the saline wetlands, especially the wetlands adjacent to the deeply incised channels. Between the three primary study sites of Raymond Road, Frank Shoemaker Marsh and the Whitehead Wetland, groundwater levels decline steeper toward the channel at Frank Shoemaker Marsh and Whitehead Wetland when compared to the Raymond Road site. Electrical conductivity values for water in observation wells, channel seeps and springs measured as high as 38,000 uS/cm. Vertical hydraulic gradients are positive at the two project sites included in the gradient calculation and this indicates upward groundwater flow. Well logs collected during observation well installation showed successive sedimentary layers of sands, silts and clays within the wetland alluvium.