SNOWMELT-ACTIVATED SHALLOW FLOW PATHS DRIVE DISSOLVED AND PARTICULATE TRACE METAL LOADING IN THE PROVO RIVER, UTAH, USA

Characterizing the routing of snowmelt to streams is critical for determining the impacts of changing land use and atmospheric deposition on water quality in mountains catchments. Trace metal concentrations typically increase in mountain streams during snowmelt runoff as metals are flushed from the watershed in dissolved and particulate forms through complex flow paths. To investigate the 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 were highest during snowmelt runoff, corresponding to relatively high concentrations in soil water. Trace metal concentrations were similar in both the dissolved and particulate forms at our upstream site. Further downstream, particulate concentrations were much higher than dissolved concentrations during runoff. The dissolved trace metal fraction was correlated with fluorescent dissolved organic matter, while the particulate fraction was correlated with turbidity. These findings suggest dissolved and particulate trace metals in the stream are sourced from soil water that is flushed by snowmelt, and trace metal transport in the stream is facilitated by dissolved organic matter and suspended sediment. Our study demonstrates that trace metal concentrations are variable during snowmelt runoff as meltwater interacts with trace metal-enriched soils along complex flowpaths. The metals interact with suspended particles or dissolved organic matter in the soil water or as they are mobilized by bank erosion or groundwater inputs. Understanding the complex interactions of snowmelt with soils during runoff has implications for improving water quality in mountain streams.