ANTHROPOGENIC EFFECTS ON EUTROPHICATION OF UTAH LAKE, UTAH SINCE EUROPEAN SETTLEMENT

A rise in the frequency of harmful algal blooms in lakes around the world has illustrated the importance of understanding the role of anthropogenic nutrients on eutrophication of shallow lakes. Recent urbanization of Utah Valley, Utah has highlighted the impacts of anthropogenically-driven eutrophication of Utah Lake, which is the 3^rd largest freshwater lake west of the Mississippi and has experienced large algal blooms. Utah Lake receives treated wastewater from adjacent communities which have grown to 650,000 residents along a narrow urban corridor.

This study examines the extent of anthropogenic contributions to eutrophication, especially since European settlement in the mid 1800’s. Three freeze cores were obtained from Utah Lake representing relatively deep, open water (4 m), a shallow embayment with emergent vegetation (Provo Bay), and Goshen Bay, which is relatively unimpacted by adjacent development. Current core chronologies are approximate and dependent on unpublished studies. Detailed chronologies of each core will be determined using the ²¹⁰Pb method.

X-Ray diffraction analysis established mineralogical differences between cores. Samples from the deep-water core contains 70-80% endogenic calcite, as well as 10-15% quartz and 10% dolomite (detrital). Provo Bay samples contains 50-60% calcite, 20-30% quartz, and 10% dolomite. Provo Bay materials clearly contain a higher detrital component.

RockEval pyrolysis was employed to characterize the organic matter (OM) in the cores and to infer the relative contributions between vascular plant and algae, with the latter expected to increase with enhanced eutrophication. Using the hydrogen index (HI), Provo Bay core exhibits a subequal balance (HI ≈ 50) between vascular plant and algal OM throughout. The deep-water core exhibits dominance by terrestrial vegetation (HI ≈ 300) until the 1950s when an increase in the influence of algae was observed. Goshen Bay OM follows a similar pattern to the deep-water core, except in the recent past there has been a return to lower HI values.

Although Utah Lake may have always been shallow and nutrient-rich, it appears that increasing urbanization has imposed increasing algal loading to the OM budget of Utah Lake sediment since the mid-20^thcentury as evidenced by large, recent algal blooms. This may be expected to continue into the future as populations increase unless improvements are made to wastewater treatment.