Fish Lake limnology and watershed aqueous geochemistry, Fish Lake Plateau, Utah

Abstract

Fish Lake is located at 2696 m elevation on the Fish Lake Plateau with a bedrock geology of Oligocene to Pliocene age volcanics and Cretaceous to Eocene age sedimentary rocks. Lake bathymetry indicates a maximum depth of ~27 m and volume of 2.31 x 108 m3. The lake is dimictic with summer water column temperature declines of 13˚C between 7 to 15 m depth, whereas in spring and fall water column is isothermal. Numerous surface streams flow into the lake and there is one surface outflow stream, Lake Creek, which drains to the northeast into Johnson Valley Reservoir and the Fremont River, which is a tributary of the upper Colorado River. Surface inflow streams and spring waters are generally dilute and ionic compositions are consistent with bedrock geology. Spring and creek water oxygen and hydrogen stable isotope compositions indicate snowmelt is the predominant water source to the lake. High evaporative enrichment is indicated by lake water stable oxygen and hydrogen compositions and conservative ions, which suggest evaporative water loss equal or greater than inflow. The ionic and isotope data combined with preliminary discharge measurements provide a preliminary estimated lake-water residence time between approximately 15 and 30 years, although groundwater flux is currently unknown. Dissolved silica concentrations decline by two orders of magnitude between inflowing waters and summer lake waters, indicating substantial uptake by freshwater diatoms and high biological productivity. During summer, epilimnion pH values of 8.7 contribute to slight oversaturation with respect to calcite/aragonite, which suggests that precipitates could form in minor concentration. Below the thermocline pH is near neutral and carbonate mineral dissolution within the water column is likely.