CHARACTERIZATION OF NONPOINT SOURCE PATHWAYS OF SALT, SE AND B IN THE PARIETTE DRAW WATERSHED, UTAH

In arid landscapes, salt, selenium (Se) and boron (B) released during weathering can become concentrated in soluble soil phases and are easily mobilized by disturbance from anthropogenic activities (farming, mining, oil/gas development and urban growth). When solubilized, these phases can cause water quality to exceed state and federal limits. The Pariette Draw (PD) Creek watershed, located in the Uinta Basin, northeastern Utah, is a tributary to the Green River and is perennial due to irrigation in the upper watershed. A BLM-managed wetland located in the lower watershed exists because of irrigation. The PD Creek is in violation of the Utah Division of Water Quality water quality criteria for total dissolved solids (TDS), Se and B, which can have negative impacts on the abundant wildlife in the wetlands. Rock, soil, surface and groundwater samples were used to identify potential geologic sources of salt, Se and B in the watershed, understand storage and transport under natural and irrigated conditions, and quantify potential flux from landuse change.

The S (sulfate is the dominant salinity source) and Se contents in Upper Green River Formation (GRF) and Lower Uinta Formation (LUF) rocks (n=55) that crop out within the watershed are generally low, with only six containing Se >2 mg kg^-1 (range <0.2-11 mg kg^-1). The Upper Uinta Formation (UUF), which is now eroded from the watershed contains abundant volcanic ash; likely the original source of S, Se, B (and U that forms roll-front deposits in the LUF). We hypothesize that these elements were weathered (oxidized/desorbed) in the past when the UUF was exposed, and transported into the LUF sandstone aquifers where they were immobilized (reduced/adsorbed). Modern weathering of the LUF causes oxidation producing sulfate, Se(VI) and desorption of B. Sulfate, selenate and borate salts form in the soil under the arid climatic conditions. Most streams are ephemeral, but redistribute these soluble phases during precipitation events. However, irrigation provides enough water in PD Creek to transport these phases from soil to wetlands and beyond throughout much of the year. Sulfate isotopes can trace origins of salinity as they are distinct within tributaries. They also help identify redox cycling within the watershed that cycles S and Se in soils during natural weathering and irrigation.