THE EXTREME ANTHROPOGENIC IMPACTS OF HUMAN ACTIVITY ON FARMINGTON BAY, GREAT SALT LAKE, USA

The Great Salt Lake is the largest saline lake in the Western Hemisphere, and Farmington Bay (FB), its large southeastern arm, has been profoundly impacted by human activity since European settlement began in 1847. It serves as a case study for wholesale modification from a shallow, hypersaline to a brackish-water ecosystem. Depending on one’s perspective, these changes may not be entirely negative. Modifications to FB has occurred in three categories: a) rerouting of stream inflows, b) restriction of water exchange from dikes and causeways with the open lake, and c) wastewater discharges including sewage and industrial effluents. Recently, large algal blooms have occurred in FB, including the summer of 2016 where high concentrations of nodularin were detected.

Material from three freeze cores has been analyzed to assess ecosystem changes and health. Core chronologies were established by ²¹⁰Pb methods. Pore-water chemistry shows that mid-20^th century causeway construction, isolating FB from exchange with the remainder of the lake, caused Cl^- to decrease from ~3700 to ~200 mg/L due to dilution from stream inflows, resulting in a brackish-water wetland. Prior to this, hypersaline water precluded diverse algal communities and diatoms were effectively absent. Coupled with freshening, emergent vegetation growth was enhanced by wastewater inflows. For example, d¹⁵N increased from as low as 4 to 10‰ following construction of a sewage canal 1911 bringing waste from Salt Lake City to FB. RockEval pyrolysis hydrogen indices (HI) of organic matter (OM) are ~100 mg-H/g-TOC prior to freshening, indicative or terrestrial sources. Afterward, a prominent excursion to as high as ~500 mg-H/g-TOC shows the increasing dominance of algal OM in sediment despite cores being located in an emergent vegetation phragmites wetland. Pore-water orthophosphate and total phosphorous trapped since 1950 ranges from a few to several tens of mg/L.

Despite the conversion of much of FB from a shallow hypersaline waterbody into excellent waterfowl habitat, nutrient loading will likely to continue to drive algal blooms due to population growth along the urban Wasatch Front corridor unless reductions are realized. Enhanced evaporation due to climate change and decreasing inflows due to water diversions will also increase relative nutrient concentrations in FB via wastewater discharges. Furthermore, high pore-water phosphorous contents may continue to release nutrients to FB due to diffusion and resuspension of sediment by storms.