Long-term trends of streamwater chemistry in an agricultural watershed: Effects of anthropogenic and climatic factors.

The chemistry of headwater streams is a key indicator of the health of riparian zones and surrounding terrestrial ecosystems. This chemistry is shaped by biogeochemical processes, including chemical weathering, and anthropogenic activities that interact with one another and are sensitive to climate. Elucidating trends in streamwater chemistry and the drivers that underpin them is essential for informing land-management decisions and anticipating water-quality issues that may affect downstream waters. In this work, we investigated the effects of anthropogenic and climatic factors on long-term variations in the chemistry of a first-order stream draining an agricultural catchment nested within the Sleepers River Research Watershed in Vermont, USA. We observed statistically significant increases in alkalinity and the concentrations of calcium and magnesium over a 31-year period for which 17 years of measurements were available. Through the application of generalized linear models, we found that the upward trends in alkalinity and calcium were associated with rising air temperatures, while a response to historical acid deposition played a minor role. We hypothesize that increased production of biogenic carbon dioxide and organic acids in soil and groundwater may lead to increases in chemical weathering rates under warmer climate conditions. This study emphasizes the important role of rising temperatures in the long-term increase in streamwater alkaline solutes, potentially overshadowing other influences like acidification recovery and agricultural practices. It also highlights the importance of comprehensive, long-term research to understand climate impacts on chemical weathering and inland water chemistry, which is critical for managing water quality and understanding regional and global carbon cycles.