Snowmelt‐Activated Shallow Flow Paths Drive Dissolved and Particulate Trace Metal Fluxes in the Provo River, Utah, <scp>USA</scp>

ABSTRACT Characterising the routing of snowmelt is critical for determining the impacts of changing land use and atmospheric deposition on water quality in mountain streams, which may show increasing trace metal concentrations during snowmelt runoff. To investigate snowmelt influence on streams, we measured trace metal concentrations in the Provo River (Northern Utah, USA) at three locations during water years 2021–2023, with complementary samples from snowpack, soil water and ephemeral streams. Dissolved and particulate trace metal concentrations in the river were highest during snowmelt, corresponding to relatively high concentrations in soil water. At our upstream site, concentrations were similar in both the dissolved and particulate forms. Further downstream, particulate concentrations were much higher than dissolved concentrations during runoff. Concentration–discharge relationships for both dissolved and particulate metals showed positive power law slopes, indicating mobilisation from the landscape. Dissolved trace metal concentrations in the river were correlated with fluorescent dissolved organic matter, while particulate concentrations were correlated with turbidity, suggesting metal sources in organic‐rich soils and suspended sediment and providing a simple method for estimating trace metal concentrations through probe measurements. Colloidal trace metal concentrations were significant in many cases, highlighting the role of particles in the ‘dissolved’ fraction. These findings suggest dissolved and particulate trace metals in the Provo River are sourced from organic‐rich soil water that is flushed by snowmelt, and trace metal transport in the river is facilitated by dissolved organic matter, colloids, and suspended sediment. Our study demonstrates the importance of trace metal flushing during snowmelt runoff as meltwater interacts with trace metal‐enriched soils along shallow flow paths and metal mobilisation by bank erosion. Understanding the complex interactions of snowmelt and soil water during snowmelt runoff has implications for improving water quality in mountain streams.