ASSESSMENT OF ANTHROPOGENIC IMPACTS ON THE UTAH LAKE (UT) USING STABLE ISOTOPE AND TRACE METAL ANALYSIS

Utah Lake and its wetlands around are critical for fish and wildlife resources, flood mitigation, and recreation, but the ecosystem is under increasing stress due to urban, industrial, and agricultural runoff from an ever-expanding population that now exceeds 500,000 people in Utah Valley, Utah. This project investigated human impacts on Utah Lake using stable isotope and trace metal analysis. A total of 13 one meter-long sediment cores were taken around the fringe of Utah Lake to capture the effect from major river inflows to the lake as well as from farm lands, wastewater treatment plants, and industrial areas around the lake. The sediment cores were subsampled at 5 cm intervals for stable isotope analysis and at 15 cm intervals for trace metal analysis.

The δ¹³C and δ¹⁵N values in the sediment cores range from -26 to -22‰ (vs. V-PDB) and from 1.17‰ to 5.04‰, respectively. The δ¹³C depth profiles show a decreasing trend from the bottom to the top of the cores which likely reflects phosphorous enrichment due to the application of commercial fertilizer and detergent utilization. In contrast, the δ¹⁵N depth profiles of lake sediment organic matter show an increasing pattern from the bottom to the top of the cores. The increase in δ¹⁵N may reflect a combination of factors, including fertilizer utilization and past untreated sewage discharge to the lake.

With respect to trace metals, their concentrations increased with depth for the majority of the metals. For instance, arsenic concentration increased from 0.19 mg/kg at the surface to 7.09 mg/kg at a depth of 100 cm. However, lead concentration in the cores showed the opposite trend with the highest concentrations in the upper sediment layers (11.35 mg/kg) and lowest in the lower sediment layers (1.66 mg/kg), perhaps indicating a constant lead input to the lake from the mining activities which are still active in the surrounding areas.