USES OF ELEMENTAL CONCENTRATIONS AND ISOTOPIC COMPOSITIONS TO DETERMINE THE SOURCES OF POSSIBLE MINING-RELATED CONTAMINANTS IN UTAH LAKE, UTAH

Recent research has documented (1) elevated concentrations of As and sulfide-mining-related heavy metals, in Utah Lake (Utah), its tributaries, and the shallow groundwater in its watershed (2) the ability of sediment transport processes to move mine tailings from historic mines to Utah Lake in the time available until creation of the reservoirs that would trap the mine tailings (3) the ability of the lineage of the perennial grass Phragmites australis that is invasive to Utah Lake to sequester As and heavy metals. The later work has shown a possible positive impact of an invasive species and has called into question the work of numerous Utah state agencies that are seeking the most efficient way to eradicate the invasive lineage. An intriguing possibility is that invasive species may have a positive impact on ecosystem health if (and perhaps only if) the ecosystem has already been negatively impacted by human activities, such as mining, in which case there would not already be an assemblage of native aquatic plants that were adapted to elevated levels of As and heavy metals. On the other hand, a non-mining-related origin for the As and heavy metals in Utah Lake cannot yet be dismissed because of the many hot springs that discharge into the lake. The objective of this study has been to compare the elemental concentrations and isotopic compositions of Utah Lake, its tributaries and its hot springs in order to determine whether rivers or hot springs are a more likely source of sulfide-mining-related contaminants for the lake. The objective was addressed by measuring concentrations of 43 elements and isotopic compositions of B and Sr at the ICP-MS Metals Lab at the University of Utah. By comparing the loading ratios of river water and groundwater sources, it was found that river water input was dominant for 32 elements, including all mining-related contaminants besides As (6.6 times greater groundwater input). Groundwater was enriched in radiogenic Sr (⁸⁷Sr/⁸⁸Sr = 0.08482) relative to river water (⁸⁷Sr/⁸⁸Sr = 0.08470), while groundwater was depleted in ¹¹B (δ¹¹B = 4.2) relative to surface water (δ¹¹B = 6.4). Based on a steady-state mass balance, lake sediments are acting as sinks for 31 elements, including all sulfide-mining-related contaminants with the exception of Ni. Further results and interpretation will be reported at the meeting.