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Incorporating 30 years of US EPA’s National Nutrient Inventory into Nationally Consistent and Spatially Explicit Catchment and Watershed Metrics
Citation:
Markley, S., M. Weber, M. Brehob, R. Sabo, M. Pennino, R. Hill, J. Compton, AND S. Alford. Incorporating 30 years of US EPA’s National Nutrient Inventory into Nationally Consistent and Spatially Explicit Catchment and Watershed Metrics. To be Presented at Oregon State University Clean Water Symposium, Corvallis, OR, April 17, 2025.
Impact/Purpose:
The National Nutrient Inventory presents a compilation of datasets quantifying N and P inputs, outputs, and management relevant metrics across the conterminous US, available at HUC12 and county scales. We used these data to provide downscaled NHDPlus catchment and accumulated watershed nutrient metrics across the conterminous US. These data present the highest resolution nutrient data available across the conterminous US and will be readily accessible through StreamCat’s Application Programming Interface and visualized through StreamCatTools. We will present case studies on using these data for surface and groundwater impaired areas of interest. Additionally, these refined data can be used to calibrate predictive models for assessing the impact of nutrient inputs and outputs on surface and groundwater and and run time series analyses on nutrient mass balances at management-relevant scales. These data can be used by a wide variety of stakeholders to support nutrient management goals. This presentation supports research being conducted under SSWR.405.1.1.4 (Quantification of nutrient inputs to conterminous US stream and lake watersheds via accumulation of nutrient inventories in StreamCat and LakeCat) and SSWR.402.2.3.4 (Expanding the use and usability of StreamCat and LakeCat watershed characterization for NARS and other EPA programs and partners).
Description:
Watershed nutrient metrics are crucial components of state-led efforts to improve nutrient reduction strategies, however, they are challenging to assemble across the scales management and research require. Therefore, we downscaled and dasymetrically allocated the EPA’s NextGen National Nutrient Inventory (NNI) to over 2.4 million subcatchments (NHDPlus V2.1) and integrated these estimates into EPA’s StreamCat database across the contiguous United States (CONUS). With the incorporation of NNI into StreamCat, we generated over 3.5 billion pieces of data, comprising three decades of nutrient estimates, resulting in a novel and robust resource to explore nutrient inputs. The new metrics cover all major sources of urban, atmospheric, wastewater, and agricultural nutrient inputs, including nitrogen and phosphorus metrics from livestock manure excretion, crop removal, fertilizer, point source loads, and atmospheric deposition. These metrics represent the highest resolution of nutrient data available across CONUS. Importantly, the watershed accumulated statistics allow seamless generation of mass balance time series that can be used to calibrate predictive models of nutrient pollution to surface and groundwater and track progress in controlling nutrient pollution sources in watersheds of interest. We will present example analyses of nutrient trends in NHDPlus V2.1 subcatchments and cumulative watersheds for surface and groundwater impaired areas. The datasets in StreamCat will be available through StreamCat’s existing Application Programming Interface and eventually accompanied by visualization functions in EPA’s StreamCatTools R package. These data provide new state-of-the-science nutrient information directly to managers and researchers aiming to understand drivers and develop solutions for improving water quality.