CHARACTERIZATION OF GREAT SALT LAKE SOUTH ARM SALT MASS AND CONCENTRATION DYNAMICS IN RELATION TO LAKE LEVEL

The Great Salt Lake (GSL) is one of the largest hypersaline lakes in the western hemisphere, providing critical habitat and food for millions of migratory birds and generating over $1 billion annually from multiple industries and recreational uses. A railroad causeway divides the GSL into North and South Arms, resulting in two water bodies with distinct water quality and biological characteristics. On July 3^rd, 2022, the GSL South Arm reached historic low lake levels, with water levels expected to continue dropping through the summer as a result of water use and ongoing drought. At low lake levels, GSL’s resident salt mass concentrates in a decreasing volume of water, leading to high salinity concentrations that exceed recommended ranges for GSL South Arm biota. To inform resource managers seeking to manage GSL water quality for multiple uses, the USGS sought to improve understanding of GSL salt mass and concentration dynamics. Routinely monitored salinity and lake level data collected in the South Arm of GSL by the USGS and state partners illustrate that: 1) seasonal fluctuations in salinity are inversely related to lake levels, and 2) stratification of the water column occurs with a persistent deep brine layer, modulating water column mixing and impacting salt and nutrient cycling. Further, quantification of salt mass fluctuations from 2011 to 2021 revealed various transient states of South Arm salt mass, controlled by the interplay between hydroclimatic variability and shifting management paradigms. From 2017 to 2021 South Arm salt mass rose steadily, amplifying increasing salinity during a period of persistent lake level decline and raising concerns of further exceedance of recommended salinity ranges.