Inland river networks regulate the export of nutrients from the terrestrial landscape, making them critical for mitigating eutrophication of downstream ecosystems. Yet the ability of rivers to process and retain nutrients has been understudied as previous research has focused mainly on small headwater streams. It is critical to understand how entire river ecosystems, not just sections of streams, influence regional and continental patterns of nutrient export to protect water resources. This research will use a novel field approach to gather empirical measurements of nutrient uptake in multiple rivers across the west and midwest and integrate the data into a dynamic network scale model to evaluate controls on nutrient uptake, thereby integrating aquatic ecosystem ecology and hydrological modeling. This approach will generate critical predictive relationships regarding the capacity of rivers spanning a range of nutrient and sediment conditions to mitigate downstream nutrient export, which is an essential step towards effective water quality management at the river network scale. The intellectual merit of the research includes the transformation of ecological theory regarding nutrient cycling in rivers and improved understanding of the ecosystem services that rivers provide. In turn, the broader impacts of the work will result in unparalleled educational opportunities for graduate students to collaborate on cutting edge river research, watershed modeling tools immediately useful to water resource managers, and data to improve emerging technologies for real-time nutrient monitoring to be used by national observatory programs.
Inland river networks regulate nutrient export from terrestrial landscapes, making them critical for mitigating pollution of downstream ecosystems, but the ability of non-wadeable rivers to mitigate nutrient pollution has been understudied relative to the headwater stream reaches that feed them. We measured nutrient removal using pulse additions of trace nutrient concentrations in 15 rivers in the Western and Midwestern USA and used a watershed model to show that river segments are hotspots of nutrient removal in river networks. The capacity of these river segments to remove nutrients was as great, if not greater than small streams. Despite measurements made across a range of biophysical conditions, there were no regional patterns in nutrient removal among the rivers we studied. We also found that rivers had high rates of algal production and ecosystem respiration and they actively process organic matter. Together, our results show that rivers have additional capacity to mitigate pollution across a variety of watersheds, and preserving this important ecosystem service should be a management priority. This project created a significant platform for innovative training of undergraduate and graduate students, all of whom added knowledge to aquatic science through their independent research. These students remain productive and active researchers in their discipline. In addition sate and tribal water quality agencies are using the techniques that we developed in this project to calculate production and respiration using their oxygen data.
