TRACE ELEMENT CONCENTRATIONS AND ISOTOPIC TRENDS ALONG A MOUNTAIN TO URBAN TRANSITION IN THE PROVO RIVER, UTAH

The Provo River is an important water resource for the >2 million people that live along the Wasatch Front in northern Utah, yet little is known about the potential changes in water quality as agricultural lands are urbanized. With undeveloped headwaters in the Uinta Mountains, an agricultural-to-urban transitional area in the middle section, and a largely urbanized lower section, the Provo River is an ideal system to study natural and anthropogenic impacts on water chemistry. The purpose of this investigation is to evaluate trace element sources along a mountain to urban transition using a variety of isotopic tracers.

We sampled surface water along a transect of the Provo River and two major tributaries on six occasions during the 2013 water year in order to characterize river chemistry across different hydrologic conditions. Samples were analyzed for a suite of trace elements (As, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, REEs, Sb, Se, Sr, Tl, U, and V), major ions, and isotopes (δ¹³C, δ¹⁵N, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr). Preliminary results show increasing concentrations of all major ions and most trace elements from upstream to downstream, as expected, with the largest increases corresponding to urban/agricultural areas. Surprisingly, concentrations of Sb and Tl decreased from upstream to downstream in the agricultural/urban areas during all sampling events, possibly reflecting either unusual in-stream geochemical processes or different sources relative to the other elements. Concentrations of Cr, Mn, Fe, Cu, Pb, and the REEs also decreased from upstream to downstream, but only during May and June, likely reflecting enhanced weathering of these elements during spring runoff or a larger contribution from soil runoff. Whereas Sr concentrations increased from upstream to downstream, ⁸⁷Sr/⁸⁶Sr ratios decreased from 0.714 to 0.709. Continued work will investigate correlations among trace element concentrations and isotopic tracers in order to differentiate trace element sources. This study has implications for improving water quality models for watersheds that are undergoing increased urbanization.