Climate and Anthropogenic Perturbations Impact Stream Geochemistry

Abstract Climate and anthropogenic perturbations, including warming temperatures, shifting precipitation patterns, and changes in contamination, can alter geochemical reactions that shape stream chemistry. To date, our understanding of how climate and humans are altering water‐rock interactions and geogenic stream chemistry is limited, partly because of the difficulty in mapping geochemical processes in the subsurface. Here, we leverage historic climatic, hydrologic, and geochemical data from 40 United States watersheds to evaluate changes in geogenic stream chemistry from 2000 to 2024. We analyze temporal trends in geogenic solutes in the context of changing precipitation, discharge, and water‐rock interactions. We show that changes in stream chemistry are variable across the U.S. and are driven by multiple drivers that impact subsurface processes over long‐timescales, including warming temperatures, changing groundwater storage, road‐salt application, and acid‐rain recovery. To fully map how climate and anthropogenic perturbations are impacting water quality, we explore the spatial and temporal heterogeneity in subsurface geochemical reactions and the propagation of the signals of those reactions into surface waters, in particular, how long‐transit times and intermediate geochemical reactions may delay in‐stream responses to perturbation.