Riverine phosphorus gain and loss across the conterminous United States

Excess riverine phosphorus represents a preeminent catalyst for water quality degradation. Spatial mapping and characterization of the net gain and loss of riverine phosphorus help discern the critical source areas. Here, we developed a dataset encompassing phosphate (PO) and total phosphorus (TP) gain and loss across catchments in the conterminous United States (CONUS). We compiled 51 394 PO and 285 675 TP concentration measurements and estimated PO and TP loads at 963 and 2317 stations, respectively. Next, we leveraged the upstream-downstream topology information from the National Hydrography Dataset Plus (NHDPlus) catchment map at the Hydrologic Unit Catalogue-12 (HUC12) level to derive the net gain and loss of riverine phosphorus across catchments in the CONUS. Such maps can be used to estimate potential contributions of point and non-point sources to riverine phosphorus pollution at refined spatial scales, identify different major factors controlling local riverine P gain and loss compared to P loads, and evaluate watershed model's fidelity for representing riverine P cycling. The resultant dataset is provided in Excel (.xlsx) format, accessible at Figshare (https://doi.org/10.6084/m9.figshare.28509317, Wang et al., 2025b). Leveraging the HUC12 information for spatialization, the new datasets aim to address the existing gap in regional characterization of riverine phosphorus and support effective management practices across the CONUS.

Impact/Purpose

The riverine P gain/loss dataset allows the estimation of riverine P removal or accrual at a refined spatial resolution to better reflect the impacts of local controls. In contrast, riverine P loads at hydrological stations embody the integrated processes from the entire upstream areas of a specific station. Also, by combining the point source inputs with the riverine P gain/loss dataset, we derived conservative estimates of the contribution of non-point sources to riverine TP (28.24 kgP km-2 yr-1). The control factor analysis with a random forest model demonstrated that the new riverine P gain/loss dataset revealed varied importance of different factors controlling riverine P removal and accrual as compared to using riverine P loads at hydrological stations. This suggests that nutrient management practices should prioritize enhancing irrigation efficiency and integrating strategies such as targeted fertilizer application and wetland restoration to effectively capture and reduce phosphorus mobilization from agricultural lands. The newly developed riverine phosphorus datasets in this study extend utility to diverse applications, encompassing, but not limited to, the evaluation of watershed models, identifying critical source areas, and optimization of agricultural management strategies. Future studies may concentrate on filling the gaps in the spatial coverage of the datasets (particularly for PO43-).

Citation

Wang, Y., X. Zhang, K. Zhao, R. Sabo, Y. Miao, AND C. Clark. Riverine phosphorus gain and loss across the conterminous United States. Copernicus Publications, Katlenburg-Lindau, GERMANY, 18(5):3355-3365, (2026). [DOI: 10.5194/essd-18-3355-2026]

DOI: Riverine phosphorus gain and loss across the conterminous United States