Judith River Watershed
Text by Caitlin Mitchell and Madison Foster
Photo Credit: Madison Boone
This summer, our team of graduate students and undergraduate interns continued efforts to investigate nitrate processing in stream-riparian corridors using direct observations of solute concentrations in ground and surface waters and continuous sensing of stream chemistry. In the riparian soils, graduate student Caitlin Mitchell coordinated the installation of groundwater sampling wells, which provide perspective on the variation in specific chemical processes.
This effort will ultimately help build confidence in our understanding of the influence of the riparian systems in mitigating nitrate loading from cultivated terrace soils to surface waters. Over the course of the spring and summer, we sampled the well and surface water sites extensively, and measured water levels in the wells to understand variability in the water table across the riparian systems of each reach.
Preliminary results suggest that removal of nitrate in the riparian subsurface is important, as groundwater nitrate concentrations are generally lower than that of the adjacent stream.
Working in the streams, graduate student Madison Foster supervised the use of high-frequency sensors to measure a suite of stream solute concentrations every 15 minutes, including nitrate, dissolved oxygen, dissolved carbon dioxide, and electrical conductivity.
We collected these data from March to August 2021, capturing a large portion of the annual hydrologic and stream metabolic regime. Drought conditions presented challenges when one stream nearly went dry. Our preliminary analyses demonstrate how both stream channel nitrate processing and connections between the stream channel and low nitrate riparian groundwaters collectively influence how stream corridors may reduce nitrate export downstream, and we are eager to dig deeper into this rich dataset.
Over the course of the summer, undergraduate student Zoe Durkin focused on an initial exploration of water level variation as part of her summer internship research, and undergraduate student Sean Williams investigated spatial variation in surface water nitrate concentrations along spring channels and the main channel for his internship research. Much of the initial analysis of this work, including the undergraduate internship research, will be presented at the virtual meeting of the Montana Chapter of the American Water Resources Association in late October. The culmination of this interdisciplinary work is a deeper understanding of how integrated riparian and stream ecosystems receive, transport, and transform nitrate loads from cultivated upland soils.
