Assessment of pollutants from the Canale d'Aiedda basin to the sea: SWAT model and Remote Sensing Approach

Water quality impairment is a concern in water resources management. During floods, a large amount of sediment and pollutants may be delivered to the river reaching the coastal zone and forming plumes that impact coastal water bodies. The present paper aims to assess spatial patterns of pollutants from the catchment to the sea, identifying the sources of nutrients within a basin, and their fate in the sea. An ecohydrological model, Soil & Water Assessment Tool (SWAT), and remote sensing techniques (Sentinel-2 imagery, processed on Google Earth Engine), using the Normalized Difference Turbidity Index (NDTI), were coupled and tested in the Canale d'Aiedda basin and Mar Piccolo Sea (Apulia, Southern Italy). The SWAT model was calibrated using daily flow and discrete sediment and nutrient concentrations. The highest specific load of total nitrogen (TN) (∼10 kg ha⁻¹y⁻¹) was simulated in the agricultural subbasins (vineyards, olive groves, and winter wheat). Similarly, the highest specific load of total phosphorus (TP) (0.7 kg ha⁻¹y⁻¹) was predicted in the subbasins where the vineyard was the prevalent crop production. NDTI was analyzed for detecting sediment concentrations in river plumes during a flash flood event (0.066 m³s⁻¹, June 10, 2023). The post-event NDTI showed increased turbidity along the coast. The results indicate that flash floods play an important role in sediment and pollutant loads delivered to the sea. This study also shows that Sentinel-2 satellite data and cloud computing enhanced turbidity monitoring into the sea or lake, complementing the SWAT results. The methodology applied in the study showed that hydrological models and remote sensing should be coupled for basins and coastal areas ecosystems protection.