Subaqueous Springs Discovered as Transport Conduits for Saline Groundwater from Depth to a Stream within the Saline Wetlands of Eastern Nebraska

Nebraska's saline wetlands are groundwater dependent ecosystems needing the upward transport of saline groundwater from the underlying Dakota Aquifer for their survival. High salinity at the wetland land surface has fostered the propagation of a number of rare endemic salt tolerant plant species. In addition, the endangered Salt Creek Tiger Beetle lives within the wetlands occupying the banks and sand bars of one of the prominent streams – Little Salt Creek - which traverses the area. Ongoing monitoring of stream salinity within this stream has detected high stream salinities, but until recently the specific mechanism for salt transport to the streams had not been identified. In the winter of 2007, during a routine foot traverse of the stream channel at low flow conditions, the authors discovered a number of subaqueous springs discharging into Little Salt Creek. These springs were typically located in shallow circular or oval spring holes ranging in size from a few millimeters to several meters in diameter. In some instances, these holes were surrounded by a raised ring of sediment. In other instances, small rolling sand boils were observed atop the spring hole. Preliminary visual observations of the springs noted the sporadic liberation of bubbles at the surface during discharge events. Discharge was typically warmer (in winter) and more saline than the surrounding stream water. The warmer discharge issuing from the springs was also observed using and infra-red camera which showed several sequential warm “blobs” of water rising (not unlike a lava lamp) to the surface and dissipating as the warmer groundwater water mixed with cooler stream water. Presently efforts are underway to determine spring flow rates and discharge event frequency, and also to measure the chemical and isotopic composition of the spring water to determine if it is upwelling Dakota saline water.