An Integrated Modeling Approach to Assess Best Management Practices (BMPs) for Improving Stream Water Quality Using the MapShed and WASP8 Models

Diffuse pollution control through the implementation of best management practices (BMPs) is essential for integrated water management. This study presents a comprehensive approach that integrates monitoring and deterministic water quality modeling to assess the effectiveness of various BMPs and point pollution control scenarios for improving water quality. The pilot study area (PSA) is the Acısu Creek watershed in the south of Turkiye. The hydrological model MapShed was employed to estimate sediment and nutrient load reductions by BMPs and these estimates were used as inputs to the Water Quality Analysis Simulation Program (WASP8) for water quality simulations. The MapShed model was calibrated in the Lower Aksu Stream basin from 2013 to 2019, achieving satisfactory results. Calibration and verification of the WASP8 model were performed using one year of monthly water quality monitoring results, showing good agreement between measurements and predictions. Diffuse pollution control scenarios were effective in decreasing pollutant concentrations. The BMP scenario for management of pastureland and livestock wastes led to total nitrogen (TN) and total phosphorus (TP) load reductions of 43% and 34% from pastureland, and 61.5% and 57.9% from farm animals, respectively, but the watershed annual loads decreased only by 4%. The combined BMP scenario targeting agricultural practices, pasture management and animal waste control provided the maximum reduction in total annual diffuse pollution loads by 35% for TN and 29% for TP. The holistic nature of this study contributes to the advancement of water quality modeling and provides valuable insights for sustainable water resources planning and decision-making.