Influence of Enhanced Silicate Weathering on Streamwater Quality: A Watershed Experiment

Enhanced Mineral Weathering (EMW), a Carbon Dioxide Removal approach, is of growing interest to scientists and practitioners due to its scalability, low technological demand, and co-benefits to farmers and soil health. Enhanced Silicate Weathering (ESW) is distinguished from EMW by grinding silicate rocks (e.g., basalt) into dust and applying it across a landscape, primarily agricultural land. After application, the silicate minerals react with carbonic acid (H2CO3) present in rainwater and soil pore water to generate weathering products such as base cations (Ca2+, Mg2+, Na+), alkalinity, trace elements (Al, Fe, Mn), and clays. These weathering products are used by plants or transported from the land to surface water. These weathering products influence streamwater chemistry by increasing in-stream pH, salinity, and alkalinity, which may worsen water quality and impair aquatic ecosystem function. Previous research has described the adverse water quality impacts of increased stream pH, salinity, and alkalinity at the continental scale across North America. The sources driving this change in freshwater quality have been identified as road salt, agricultural lime, and strong acids derived from anthropogenic activities (e.g., fertilizer and acid mine drainage). We are interested in understanding how ESW deployed at large scales may contribute to ongoing changes in freshwater quality. Here, in a small agricultural watershed in Northeastern Vermont, United States, we monitor water quality pre- and post-application of basalt at high-frequency intervals at two stream locations (measuring temperature, pH, specific conductance, dissolved oxygen, chlorophyll-a, and CDOM). In addition, we collected weekly baseflow water samples and stormwater samples across 19 rain events. All water samples were measured for a suite of chemical parameters, including DOC, alkalinity, major anions, cations, trace elements, and water isotopes. We analyze this data through multiple lenses, estimating changes to water quality, describing concentration-discharge dynamics, and analyzing aquatic ecosystem response via community respiration.