A Paleolimnological History of Metals Contamination and Eutrophication in the Great Salt Lake

Multiple sediment cores were used to address how metals contamination and eutrophication has changed over the last 200 years in the Great Salt Lake. The cores from Gilbert and Farmington Bay were sectioned in 0.5-cm intervals, and analyzed for metals & various metrics of nutrient loading and algal growth. Metal concentrations in the cores from Gilbert Bay showed increases that paralleled the known production of the specific metals in Utah. For example, lead in the sediments increased 20 to 40-fold above background levels (pre-1850) and peaked from 1930-1950, coincident with the years of highest production of lead by smelters. However, since the 1950s, concentrations of most metals have declined to 20-40% of the peak levels, likely as a consequence of decreased mining (e.g. lead and zinc), or cleaner smelting technologies (e.g. copper). Consequently, the paleolimnological record indicates that most of the high metal concentrations in the lake are a legacy effect of unregulated smelting practices in the 20th century. Despite the decreasing concentrations for many metals, levels of selenium, copper, arsenic, mercury, cadmium, lead and zinc in the surficial sediments are still above Threshold Effect Concentrations, suggesting that we still need to be concerned with the metals in the lake sediments. The sediment cores also documented eutrophication in both Farmington and Gilbert Bays. In Farmington Bay eutrophication metrics indicated that the system has changed from a mesotrophic ecosystem with submerged aquatic marcrophytes to a hypereutrophic condition. In Gilbert Bay, fossil pigments of algae, nitrogen content and other parameters are now 3 to \u3e10 fold higher in surficial sediments than in those deposited 150 years ago. Brine shrimp cysts are much more abundant in recent sediments of Gilbert Bay than in early sediments, likely because the lake was frequently too salty to support shrimp prior to the construction of the Southern Pacific Railway Causeway in 1959, and because eutrophication has provided additional food for the shrimp. Brine shrimp \u3e200 years old were hatched from cysts preserved in the sediments