Nitrate Memoryscape: Point and Non-Point Source Controls on Stream Nitrogen Export
Abstract
Worldwide increases in reactive nitrogen (N) flows are driven by increases in population, shifting diets, and increased use of commercial N fertilizers. Excess N flows threaten drinking water quality, disrupt aquatic ecosystems, and fuel coastal algal blooms. Awareness surrounding the impacts of excess N in the environment has spurred concerted efforts to reduce the overall terrestrial N load. Despite such efforts, N export has, in many cases, been either increasing or not shown any significant decline. The apparent lack of success in meeting water quality goals can be attributed to inadequate measures taken to reduce N export and time lags between implementing conservation measures and seeing measurable changes in water quality. A comprehensive understanding of linkages among landscape-scale N management practices, the accumulation of N in the landscape, and stream N export is required for effective watershed management. In the present study, we explore spatial and temporal variability in relationships between N inputs and stream N export across the contiguous US. We have synthesized long-term N input and stream N export trajectories for over 400 watersheds. We show that the relationship between landscape N inputs and stream N export varies spatially, controlled by both land management and hydrologic connectivity. We further find that N input and export trends can change over time within individual watersheds, leading to nonlinear, hysteretic relationships between changing N inputs and stream export. We find evidence of both clockwise and counterclockwise hysteresis loops across the landscape, with these patterns being related to the dominant sources of inputs, legacy N accumulation in various landscape compartments, as well as landscape attributes. A better understanding of watershed nutrient processing and the role of the landscape, climate, and legacy N in controlling water quality is crucial for better policy and better environmental outcomes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.U32B..06B