Towards sustainable river health: integrating hydrological modeling to predict nitrogen and phosphorus loads in the lower Sutlej sub-basin, Punjab, India

ABSTRACT This research evaluated the total nitrogen (TN), nitrate nitrogen (NO3-N), and total phosphorus (TP) loads of the lower Sutlej sub-basin using the Soil and Water Assessment Tool (SWAT) model. The model simulated TN, NO3-N, and TP successfully with satisfactory values of R2, NSE, PBIAS, and RSR. The streamflow and nutrient loss were found to be most sensitive to curve number and organic phosphorus enrichment ratio, with a sensitivity ratio of 0.661 and 0.556, respectively. Simulated TN, NO3-N, and TP loss within the basin vary from 6.32 to 14.23, 0.49 to 1.81, and 2.02 to 4.10 kg/ha/yr, respectively. Maximum and minimum TN losses were 14.23 and 6.32 kg/ha/yr in WS2 and WS5, respectively. Similarly, NO3-N losses were 1.81 and 0.49 kg/ha/yr in WS6 and WS10, respectively. WS2 and WS5 observed maximum and minimum TP loss of 4.10 and 2.02 kg/ha/yr, respectively. The watersheds located in the northeastern part of the basin contributed the highest nutrient load of TN (2,709 tons for WS12), NO3-N (214 tons for WS6) and TP (729 tons for WS12). By addressing nutrient losses and implementing suggested conservation measures, the present research findings can offer valuable guidance for managing sub-watersheds to reduce the nutrient loads and manage the health of the Sutlej River in Punjab.