Event Title

Evaluating Dust Contributions to the Solute Chemistry of Mountain Streams in Northern Utah

Presenter Information

Hannah Checketts
Natalie Shepherd

Location

USU Eccles Conference Center

Event Website

http://water.usu.edu

Start Date

4-5-2016 4:42 PM

End Date

4-5-2016 4:45 PM

Description

Wind-blown dust is an important flux to mountain snowpack, with potentially significant contributions of trace metals and solutes to mountain streams during snowmelt. However, it is difficult to differentiate dust contributions in runoff from soil erosion and weathering inputs. Sr isotopes show promise as a tracer of the soluble fraction of dust through the hydrologic system. We analyzed 87Sr/86Sr ratios, Sr concentrations, and other parameters in bulk snowpack (wet and dry deposition), dust, and snowmelt runoff in three snowmelt dominated watersheds in northern Utah during snowmelt in 2014 and 2015. The Provo River, Logan River, and Little Cottonwood Creek watersheds were selected because they provide contrasting geologic settings to evaluate dust contributions to water chemistry. Sr concentrations and 87Sr/86Sr ratios ranged across the watersheds and varied throughout the snowmelt season. For each sampling site, a two component mixing model was developed with end members of bulk snowpack (dominated by dust contributions) and pre-runoff river baseflow (assumed to represent groundwater contributions). Mixing models for the upper Provo River at the Soapstone sampling site indicated that about 40% of the Sr load was from dust during the 2014 snowmelt season at peak runoff, with early season samples plotting below the mixing line likely due to soil water contributions. In 2015, mixing models indicated that dust contributed about 20% of the Sr load at Soapstone. Further downstream on the Provo River at the Hailstone sampling site, mixing models were less conclusive because the majority of stream samples did not plot on the mixing line. Soil water is perhaps the dominant source of Sr at Hailstone with a larger watershed and more complex lithology relative to the Soapstone site. Likewise, water samples collected at Little Cottonwood Creek did not plot on the mixing line with endmembers of snowpack and groundwater, suggesting that soil water is a more important source of Sr relative to dust. At the Logan River, mixing models indicate that approximately 20% of the Sr load in the river was from dust. These preliminary 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 solute loads in mountain streams. Further work is underway along the upper Provo River, utilizing additional isotopic tracers such as ?11B and ?34S to provide more evidence of dust contributions to stream solute loads. Mixing models will be improved by adding measurements of solute and isotopic composition of soil water. Also, work on measuring DOM will be done for the purpose of understanding trace metal transport with organic material.

Comments

A poster by Hannah Checketts, who is with Brigham Young University, Geological Sciences

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Apr 5th, 4:42 PM Apr 5th, 4:45 PM

Evaluating Dust Contributions to the Solute Chemistry of Mountain Streams in Northern Utah

USU Eccles Conference Center

Wind-blown dust is an important flux to mountain snowpack, with potentially significant contributions of trace metals and solutes to mountain streams during snowmelt. However, it is difficult to differentiate dust contributions in runoff from soil erosion and weathering inputs. Sr isotopes show promise as a tracer of the soluble fraction of dust through the hydrologic system. We analyzed 87Sr/86Sr ratios, Sr concentrations, and other parameters in bulk snowpack (wet and dry deposition), dust, and snowmelt runoff in three snowmelt dominated watersheds in northern Utah during snowmelt in 2014 and 2015. The Provo River, Logan River, and Little Cottonwood Creek watersheds were selected because they provide contrasting geologic settings to evaluate dust contributions to water chemistry. Sr concentrations and 87Sr/86Sr ratios ranged across the watersheds and varied throughout the snowmelt season. For each sampling site, a two component mixing model was developed with end members of bulk snowpack (dominated by dust contributions) and pre-runoff river baseflow (assumed to represent groundwater contributions). Mixing models for the upper Provo River at the Soapstone sampling site indicated that about 40% of the Sr load was from dust during the 2014 snowmelt season at peak runoff, with early season samples plotting below the mixing line likely due to soil water contributions. In 2015, mixing models indicated that dust contributed about 20% of the Sr load at Soapstone. Further downstream on the Provo River at the Hailstone sampling site, mixing models were less conclusive because the majority of stream samples did not plot on the mixing line. Soil water is perhaps the dominant source of Sr at Hailstone with a larger watershed and more complex lithology relative to the Soapstone site. Likewise, water samples collected at Little Cottonwood Creek did not plot on the mixing line with endmembers of snowpack and groundwater, suggesting that soil water is a more important source of Sr relative to dust. At the Logan River, mixing models indicate that approximately 20% of the Sr load in the river was from dust. These preliminary 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 solute loads in mountain streams. Further work is underway along the upper Provo River, utilizing additional isotopic tracers such as ?11B and ?34S to provide more evidence of dust contributions to stream solute loads. Mixing models will be improved by adding measurements of solute and isotopic composition of soil water. Also, work on measuring DOM will be done for the purpose of understanding trace metal transport with organic material.

https://digitalcommons.usu.edu/runoff/2016/2016Posters/28