Search

Quantifying the routing of snowmelt to surface water is critical for predicting the impacts of atmospheric deposition and changing land use on water quality in montane catchments. To investigate solute sources and streamflow in the montane Provo River watershed (Utah, USA), we used time‐series 87Sr/86Sr ratios sampled at three sites (Soapstone, Woodland and Hailstone) across a gradient of bedrock types. Soils are influenced by aeolian dust contributions, with distinct 87Sr/86Sr ratios relative to siliciclastic bedrock, providing an opportunity to investigate shallow versus deeper flow paths for controlling water chemistry. At the most upstream site (Soapstone), Sr concentrations averaged ~17 μg/L with minimal dilution during snowmelt suggesting subsurface flow paths dominated streamflow. However, a decrease in 87Sr/86Sr ratios from ~0.717 during baseflow to as low as ~0.713 during snowmelt indicated the activation of shallow flow paths through dust‐derived soils. In contrast, downstream sites receiving water inputs from Sr‐rich carbonate bedrock (Woodland and Hailstone) exhibited strong dilution of Sr from ~120 to 20 μg/L and an increase in 87Sr/86Sr ratios from ~0.7095 to ~0.712 during snowmelt. A three‐component mixing model using 87Sr/86Sr ratios and Sr concentrations at Soapstone showed water inputs were dominated by direct snowmelt and flushed soil water during runoff and groundwater during baseflow. At Woodland and Hailstone, a two‐component mixing model showed that the river was a mixture of groundwater and up to 75% upstream channel water during snowmelt. Our findings highlight the importance of flushed soil water for controlling stream water discharge and chemistry during snowmelt, with the signal from the upstream site propagating downstream in a nested catchment. Further, aeolian dust contributes to the solute chemistry of montane streams with potential impacts on water quality along shallow flow paths. Potential contaminants in these surface soils (e.g., Pb deposition in dust) may have significant impacts on water quality during snowmelt runoff. [ABSTRACT FROM AUTHOR]

• Urban and snow dust have a similar grain size distribution, mineralogy, and chemistry as playa dust. • Playas contribute the majority of dust to the urban Wasatch Front and mountain snowpack. • Urban aerosols contribute substantial amounts of anthropogenic trace elements. • Specific elements in dust are soluble and readily available in the environment. Atmospheric deposition to urban areas and mountain snowpack often contains a mixture of playa dust and anthropogenic aerosols, yet the relative contribution of trace elements from each source is not well understood. To evaluate dust contributions from regional playas to an urban area, we sampled playa dust sources, urban dust deposition, and snow dust deposition across the Wasatch Front in northern Utah, USA. Dust samples were analyzed for trace and major element chemistry, grain size distribution, and mineralogy. Playa, urban, and snow dust samples contained similar mineralogy, dominated by silicate, carbonate, and evaporite minerals. Grain size distribution between playa, urban, and snow dust samples was also similar, suggesting that playas are a primary dust source for the region. Principal component analysis and enrichment diagrams revealed similar chemistry of playa, urban, and snow dust with some exceptions. Compared with playa dust, urban and snow dust had lower concentrations of Li, Na, Sr, U, Mg, and Ca and higher concentrations of Fe, Al, Be, Sb, Se, Mo, Cr, La, and Cu. The first set of elements are found in evaporite- and carbonate-minerals while the second set of elements are sourced from anthropogenic activities. Mass balance calculations suggest that 90% of the dust mass deposited to the Wasatch Front is from playas, with small additions from local sources that alter the dust chemistry. Sequential leaching of dust samples showed that some elements were readily leached with weak acids, including B, K, Na, Sr, Ca, U, Mo, Cd, and Se, suggesting that they are environmentally available and may serve as important macronutrients or contaminants to ecosystems. This is the first study to directly compare the geochemistry of playa dust sources with dust deposition to urban areas and mountain snowpack in the western US, with implications for understanding how water diversions, land use changes, and population growth may affect the regional dust cycle in the future. [ABSTRACT FROM AUTHOR]