Snowmelt river systems exhibit seasonal fluxes in water chemistry, potentially affecting the water supply of one-sixth of the worlds population. In this study, we examined water chemistry of the upper Provo River, northern Utah, which supplies water to over two million people along the urban Wasatch Front. Seasonal changes in water chemistry were characterized by analyzing discharge and dissolved organic carbon (DOC) with dissolved trace metal and cation concentrations (La, Pb, Cu, Al, Be, Sr and K) over three consecutive water years 2014”2016, with intensive sampling during snowmelt runoff. To better understand links between metal movement and DOC, we sampled the river in three locations (Soapstone, Woodland, and Hailstone), snowpack, and ephemeral snowmelt channels. Concentrations of La, Pb, Cu, Al, and Be increased with discharge/snowmelt during the 2014, 2015 and 2016 water years. Over 90% of La, Pb, Cu, Al, Be and between 70-90% Sr and K loads occurred during the snowmelt season (April-June). In relation to discharge, concentrations of each element varied between the river sampling sites. At Soapstone, DOC, La, Pb, Cu, Al and Be increased slightly with discharge, but Sr and K remained chemostatic. At Woodland and Hailstone, DOC, La, Pb, Cu, Al and Be had sharp increases with discharge, and Sr and K were diluted. Hysteresis patterns showed that concentrations of DOC, La, Pb, Cu, Al, Be, Sr and K all peaked on the rising limb of the hydrograph at the higher elevation Soapstone site but patterns were variable at the lower elevation Woodland and Hailstone sites. Concentrations for ephemeral channels were significantly higher than river and snow concentrations in La, Pb, Cu and Al, suggesting soil water was a significant source of flushed metals and DOC to the upper Provo River. DOC was highly correlated with La (R2 = 0.94, P = <<> .0001), Pb (R2 = 0.76, P = <<> .0023), Cu (R2 = 0.83, P = <<> .0001), Al (R2 = 0.94, P = <<> .0001) and Be (R2 = 0.93, P = <<> .0005), and likely facilitating metal transport. More work is needed to determine the mechanisms of DOC and metal transport, and potential metal complexation. This study has implications for understanding water quality impacts from metal flushing during snowmelt in mountain watersheds.

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