Remote observations of particulate inorganic phosphorus concentration in three large waters of China over the past 25 years

Phosphorus exerts a critical biogeochemical effect in the eutrophication process, and particulate inorganic phosphorus concentration (C PIP ) is considered an important water quality indicator for evaluating human and environmental impacts on aquatic ecosystems. However, its monitoring remains challenging due to the lack of long-term recorded data. Using field measurements and image-matched data collected from three large lakes (Lake Taihu, Lake Hongze, and Lake Chaohu) of Eastern Plain of China, we calibrated and developed two new algorithms suitable for Moderate Resolution Imaging Spectrometer (MODIS) and Sentinel-3 Ocean and Land Color Imager (OLCI) data to estimate C PIP . Validations suggested that the developed models presented appreciable performance for estimating C PIP , with a mean absolute percentage error (MAPE) below 24%, root mean square error (RMSE) less than 0.025 mg/L, and normalized root mean square error (NRMSE) below 9.5%. Subsequently, the MODIS and OLCI data were utilized to reveal the 25-year spatiotemporal patterns of C PIP in three target lakes. Mann-Kendall and Sen's slope analyses demonstrated an overall increasing trend in C PIP of three observed lakes from 2001 to 2025 with significant spatiotemporal heterogeneity, which was driven by the distinct different effects of hydrological stresses and anthropogenic activities. Importantly, this study provides the first long-term recorded dataset of C PIP targeting inland water bodies, thereby offering an integrated approach and novel insights for advancing precise eutrophication control and efficient aquatic environmental management.