Pradeep Ramtel, Dongmei Feng
Abstract Total phosphorus (TP) concentration impacts river ecosystems, yet its dynamics remain poorly understood in the contiguous United States (CONUS). We used an XGBLinear model to estimate riverine TP solely from Landsat reflectance data. Using this model, we developed a remotely estimated riverine TP database (CONUS’s Landsat-based Estimation and Assessment of Riverine TP, CLEAR-TP), covering 33,497 river reaches (107,000 km in river length) from 1984 to 2018. Using CLEAR-TP, we estimated long-term (≥15 years) annual TP concentrations for 16,258 reaches, and long-term TP trend analysis indicates that most reaches (13,092; 80.53%) exhibited stationary TP trends, while 3,166 reaches (19.47%) showed significant long-term trends, including 2,637 reaches (16.22%) with declining TP (−0.995%/year on median) and 529 reaches (3.25%) with increasing TP (1.216%/year on median). CLEAR-TP reliably captured longitudinal variations in TP concentrations along river profiles. Our results suggest that, at the reach scale, TP trends in reaches with significant trends, and, at the river-course scale, longitudinal spatial variations in most CONUS rivers, were primarily associated with climate, hydrology, and land cover.