SALT DISTRIBUTION AROUND ALKALI LAKE, NEBRASKA SAND HILLS, U.S.A

Saline lakes are commonly found in the arid environment of the Nebraska Sand Hills where evaporation exceeds precipitation. Fresh groundwater with total dissolved solids of 0.3 g/L enters the lakes while evaporation increases salinity to greater than 100 g/L in some lakes. Age of lake bed sediments in Alkali Lake, a gaining lake in Garden County, Nebraska was found to be approximately 6000 years before present from optically-stimulated luminescence and diatom analysis. With existing climatic conditions, lake salinity would be in excess of concentration of mineral precipitation, i.e. on the order of 200-300 g/L. In addition, thick layers of mineral deposits would be expected. However, Alkali Lake has salinity ranging only from 35 to 85 g/L and thin salt crusts forming seasonally along the lake beach. Aeolian transport is a mechanism that may reduce lake salinity in the absence of convective and advective discharge of lake water into the ground. To assess surface crust density, 10.8-cm diameter samples of cohesive salt crusts were collected along lake beaches. To assess salt distribution at the soil surface, a 10.8-cm diameter and 3.8-cm deep cylinder was used to gather samples of the substrate, beneath the site where salt crusts were collected, and dune sands along eight radial directions, separated 45 degree apart, and up to 800 m away from lake. Specific electrical conductivity of aqueous extracts of the samples was measured in the laboratory and converted to salt mass using a previously derived calibration curve. Surface salt crust density ranged from 0.23 to 2.95 kg/m²; volumetric substrate salt density ranged from 14.4 to 94.8 kg/m³; and volumetric dune salt density ranged from 0.14 to 3.91 kg/m³. Preliminary analysis of the spatial salt distribution indicates that Aeolian transport, controlled by hydrology, climate, and topography, may play a significant role in lake salt balance in the region.