RANKING BASINS ACROSS THE CONTIGUOUS U.S. TO DETERMINE WHERE SEDIMENT IS LIKELY A CONCERN: HOTSPOTS AND IMPORTANT CONSIDERATIONS FOR ENVIRONMENTAL JUSTICE

Nearly half of streams in the United States have been declared as having fair to poor conditions for aquatic ecosystem health by the U. S. Environmental Protection Agency because of sediment issues. Understanding gaps in sediment data used to quantify geomorphic processes that affect erosion, transport, and deposition of sediment is important in managing sediment as a problem and is crucial for prioritizing research and monitoring. We compiled several datasets across the contiguous U.S. (CONUS) to rank river basins defined by the National Hydrography Dataset (NHD) 4-digit Hydrologic Unit Codes (HUC4s) to determine where sediment is likely to be a concern. Our analysis ranked 163 basins regionally within 18 NHD HUC2 regions and nationally across CONUS. We applied understanding of geomorphic processes to select variables for the analysis, which were organized into six variable groups: 1) physiographic setting (e.g. surface deposits, soils), 2) modeled sediment and phosphorus concentrations and yields, 3) anthropogenic factors and land use, 4) hydrologic conditions (e.g. precipitation, runoff), 5) ecosystem sensitivity (e.g. metrics of stream health), and 6) socioeconomic considerations (e.g. income, percent people of color, community resilience). We eliminated variables that were moderately to highly correlated (p ≥ 0.6) and used principal component analysis to retain variables that explained the highest variability in multidimensional space. Variable contributions to the first two PCA axes were used to weight 33 variables within each region in the regional analysis and across CONUS in the national analysis. Higher weights were assigned to variables that explained more variability in the multivariate dataset. Results from the regional analysis provide a useful tool to identify basins where sediment is likely to be a concern in each region. National results indicate a hotspot of highly ranked basins in the Midwest and a band of moderately ranked basins across the south-central U.S. into the Southwest. Examination of ranks for each variable group provide important insights, including a hotspot for socioeconomic considerations in the southwestern U.S. Our findings highlight the importance of including socioeconomic data when prioritizing areas for sediment research and monitoring needs.