INVESTIGATING TRANSPORT OF DUST-BORNE TRACE ELEMENTS FROM SNOWPACK TO SNOWMELT RUNOFF IN THE PROVO RIVER, UTAH

Aeolian dust is an important physical and chemical flux to mountain snowpack with potentially significant contributions of trace elements to mountain streams during snowmelt. However, it is difficult to differentiate solute contributions from dust relative to soil erosion and bedrock weathering. Sr isotopes show promise as a tracer of the soluble fraction of dust through the hydrologic system. We analyzed ⁸⁷Sr/⁸⁶Sr ratios, Sr and other trace element concentrations in bulk snowpack (wet and dry deposition), dust, and snowmelt runoff in the upper Provo River watershed in the Uinta Mountains (Utah, USA) over three years (2014-2016). Preliminary results using a two end-member mixing model (end-members of bulk snowpack and river baseflow) indicate that dust contributed up to 40% of Sr riverine load during peak runoff in 2014. In contrast, in 2015 the river Sr data plotted off the mixing line suggesting a different source of solutes. Analyses are ongoing for the 2016 samples. Sequential leaching experiments of dust samples show that Sr is likely associated with the highly soluble carbonate mineral fraction in dust, but other elements such as Cr, Cu, Pb, and U are associated with the relatively insoluble organic fraction. Additional work is underway to investigate transport of these less soluble dust-borne metals during snowmelt by complexation with organic matter or other mechanisms. These results suggest that dust on snowpack is an important but variable source of soluble elements during snowmelt, and that dust should be considered when investigating trace element loads in mountain streams.