Thermal groundwater contributions of arsenic and other trace elements to the middle Provo River, Utah, USA

Groundwater inputs can impact river water quality but are difficult to disentangle from agricultural, urban, and storm runoff. To better understand the multiple processes affecting water quality, we used major solute and trace element concentrations with continuous measurements of flow rates and specific conductance to track temporal and spatial changes in surface water and groundwater solute inputs into the middle Provo River, located in northern Utah, USA. Thermal groundwater was the most important source of major solutes and trace elements to the middle Provo River, with concentrations of As, B, Cs, Li, Sr, and Rb increasing dramatically (twofold to tenfold) downstream of thermal water inputs in the Snake Creek tributary. Snake Creek accounted for only 20% of the flow to the Provo River but increased the As concentrations ~four-fold. Diffuse groundwater inputs, including thermal water, along the Provo River also contributed a measureable increase in solute concentrations. Mixing calculations indicate that groundwater contributed up to 10% of the total streamflow to the middle Provo River, causing an increase in thermal groundwater-derived trace element concentrations. In addition to natural groundwater inputs, water quality was impacted by anthropogenic trace and major element inputs from surface water tributaries. Nitrate, Ba, and V concentrations increased substantially downstream of agricultural/urban inputs. Specific conductance data showed that tributaries added solutes to the Provo River during runoff events, likely from the washoff of road salts. With evidence of both natural and anthropogenic inputs of trace and major elements to the middle Provo River, our study has implications for understanding water quality in complex coupled human–natural systems and demonstrates the influence of thermal groundwater inputs on water quality where such systems discharge.