REGIONAL GROUND-WATER AND SALT TRANSPORT FLOW PATTERNS OF EASTERN NEBRASKA'S SALINE WETLANDS

Eastern Nebraska's saline wetlands are the most limited type of wetland in the state, have a long history of anthropogenic degradation and are home to endangered plant and insect species. Since 1993, conceptual models of the wetland areas have been developed according to continuous research. The saline wetlands are associated with the Rock and Little Salt Creek watersheds along with the Maha, or Dakota, aquifer. Derived from both terrestrial and marine depositional environments, this Cretaceous-age aquifer is a sedimentary system of interbedded clay, silt and sand units. This environment has created a complex system of ground-water flow routes, and from the flow regime, unique geochemistry. Measured concentrations of NaCl range from 5,900 to 15,700 mg/L across the study sites. Research indicates that the occurrence of salt is not from evaporative concentration at the surface, but rather from a deeper, hydrogeologic source, likely the underlying Pennsylvanian deposits. An upward vertical gradient, up to 0.04 in Rock Creek, aids in discharging salt water to the ground surface.

The conceptual model is now being expanded into the uplands around the wetlands. Four multi-level, monitoring well nests with transducers were installed in the areas surrounding the Rock Creek study site. The purpose of these new wells is to help establish regional flow patterns and salt transport pathways. Test hole drilling also has expanded the hydrogeologic understanding of the region. In summer of 2005, a suite of chemical samples will be taken, including major ions and isotopes to further constrain these flow systems and to explore the mixing relationships between them. It is expected that TDS at the deepest sampling depths, near the Dakota-Pennsylvanian contact, will be higher than indicated in any of the central wetland samples.