Modelling of discharge, nitrate and phosphate loads from the Reda catchment to the Puck Lagoon using SWAT

Abstract

Modelling of discharge, nitrate and phosphate loads from the Reda catchment to the Puck Lagoon using SWAT. This study presents an application of the SWAT model (Soil and Water Assessment Tool) in an agricultural, coastal catchment situated in northern Poland, draining an area of 482 km2 (the Reda catchment). The main objective of this study was calibration and validation of the model against daily discharge and water quality parameters (bi-monthly total suspended solids [TSS], nitrate nitrogen [N-NO3] and phosphate phosphorus [P-PO4] loads). Calibration and validation were conducted using the SWAT-CUP program and SUFI-2 (Sequential Uncertainty Fitting Version 2) algorithm. The Nash- -Sutcliffe efficiency, which was set as an objective function in calibration of all variables, was equal for discharge to 0.75 and 0.61 for calibration and validation periods, respectively. For TSS, N-NO3 and P-PO4 loads NSE was equal to 0.56, 0.62 and 0.53 in calibration period, and 0.22, 0.64 and -1.78 in validation period, respectively. For the calibration period all the results are satisfactory or good, while for the validation period the results for TSS and P-PO4 loads are rather poor, which is related mainly to the lack of homogeneity between calibration and validation periods. These results demonstrate that SWAT is an appropriate tool for quantification of nutrient loads in Polish agricultural catchments, in particular for N-NO3. The model can therefore be applied for water resources management, for quantification of scenarios of climate and land use change, and for estimation of the Best Management Practices efficiency