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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‐series⁸⁷Sr/⁸⁶Sr ratios sampled at three sites (Soapstone, Woodland and Hailstone) across a gradient of bedrock types. Soils are influenced by aeolian dust contributions, with distinct⁸⁷Sr/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 in⁸⁷Sr/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 in⁸⁷Sr/⁸⁶Sr ratios from ~0.7095 to ~0.712 during snowmelt. A three‐component mixing model using⁸⁷Sr/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. It is well understood that the distribution and quantity of liquid water in snow is relevant for snow hydrology and avalanche forecasting, yet detecting and quantifying liquid water in snow remains a challenge from themicro- to the macro-scale. Using near-infrared (NIR) spectral reflectancemeasurements, previous case studies have demonstrated the capability toretrieve surface liquid water content (LWC) of wet snow by leveraging shifts in the complex refractive index between ice and water. However, different models to represent mixed-phase optical properties have been proposed, including (1) internally mixed ice and water spheres, (2) internally mixed water-coated ice spheres, and (3) externally mixed interstitial ice and water spheres. Here, from within a controlled laboratory environment, we determined the optimal mixed-phase optical property model for simulating wet snow reflectance using a combination of NIR hyperspectral imaging, radiative transfer simulations (Discrete Ordinate Radiative Transfer model, DISORT), and an independent dielectric LWC measurement (SLF Snow Sensor). Maps of LWC were produced by finding the lowest residual between measured reflectance and simulated reflectance in spectral libraries, generated for each model with varying LWC and grain size, and assessed against the in situ LWC sensor. Our results show that the externally mixed model performed the best, retrieving LWC with an uncertainty of ∼1 %, while the simultaneously retrieved grain size better represented wet snow relative to the established scaled band area method. Furthermore, the LWC retrieval method was demonstrated in the field by imaging a snowpit sidewall during melt conditions and mapping LWC distribution in unprecedented detail, allowing for visualization of pooling water and flow features. 

Abstract Effective snow grain radius ( r e ) is mapped at high resolution using near-infrared hyperspectral imaging (NIR-HSI). The NIR-HSI method can be used to quantify r e spatial variability, change in r e due to metamorphism, and visualize water percolation in the snowpack. Results are presented for three different laboratory-prepared snow samples (homogeneous, ice lens, fine grains over coarse grains), the sidewalls of which were imaged before and after melt induced by a solar lamp. The spectral reflectance in each ~3 mm pixel was inverted for r e using the scaled band area of the ice absorption feature centered at 1030 nm, producing r e maps consisting of 54 740 pixels. All snow samples exhibited grain coarsening post-melt as the result of wet snow metamorphism, which is quantified by the change in r e distributions from pre- and post-melt images. The NIR-HSI method was compared to r e retrievals from a field spectrometer and X-ray computed microtomography (micro-CT), resulting in the spectrometer having the same mean r e and micro-CT having 23.9% higher mean r e than the hyperspectral imager. As compact hyperspectral imagers become more widely available, this method may be a valuable tool for assessing r e spatial variability and snow metamorphism in field and laboratory settings.