HYDROGEOCHEMISTRY OF RIPARIN WETLANDS ALONG THE PLATTE RIVER IN EASTERN NEBRASKA

The Nebraska Army National Guard Camp Ashland Training Site lies along the Platte River near Ashland, Nebraska. Surrounding land is primarily agricultural, with some urban areas. Water from seven wetlands, four groundwater wells and the Platte River on this site was sampled three times during the period from May to November 2006 at the request of The National Guard for the purpose of compiling general information on the health of these wetlands, assessing their evaporative behavior, defining their connection to groundwater and characterizing the geochemical evolution of dissolved constituents. Initial samples were collected, or measurements were made in the field, for pH, conductivity, temperature, total phosphorus, total nitrogen, dissolved oxygen, dissolved organic carbon, major cations, major anions and chlorophyll-A. Samples were also collected and analyzed for deuterium and oxygen-18 in an effort to assess connectivity between the Platte River, the wetlands, and groundwater and to determine the impact of evaporation on surface waters within the wetland. Preliminary wetland results indicate that most values are within typical ranges for pH, major ions and temperature with the exception of one wetland which exhibited a temperature close to that which would be expected for local groundwater, indicating a possible groundwater source for that wetland. Total phosphorus and phosphate trends vary seasonally and may reflect the receipt of agricultural runoff in spring months. Nitrogen as nitrate was not detected in significant amounts in these wetlands, indicating that they may be receiving water in higher proportions from groundwater than surface runoff or precipitation.