Four decades of suspended particulate matter concentrations in the Po River revealed by landsat satellites

Suspended particulate matter (SPM) is a key indicator of both sediment transport and water quality in river environments. In this study, a comprehensive long-term analysis of SPM concentrations in the Po River, the longest in Italy, was carried out over the period 1984-2024 by applying a well-established semi-empirical SPM retrieval algorithm to multispectral satellite imagery collected from Landsat-5, -7, -8 and -9. The spatial distribution, seasonal variations and temporal trends of Landsat-derived SPM concentration, that strongly matched field data (R2 = 0.86) were then combined with hydrological observations. The results show that SPM concentrations in the Po River have ranged from 1.2 to 55.9 mg/L over the past four decades, and that the concentration values generally increased downstream and peaked in the spring. Time-series decomposition showed consistent seasonal patterns and long-term trend changes, characterized by a gradual increase until 2005, followed by a marked decline. A non-linear relationship was observed between SPM and discharge. This study demonstrates the efficiency of satellite remote sensing as a tool for watershed management and environmental assessment, and provides a scientific basis for large-scale, long-term water quality monitoring in the Po River.