Evaluating efficiencies and cost-effectiveness of best management practices in improving agricultural water quality using integrated SWAT and cost evaluation tool

Agricultural conservation practices, or agricultural best management practices (BMPs), can reduce nutrient loading and help address harmful algal blooms (HABs). HABs in the western basin of Lake Erie, which are largely caused by phosphorus losses from the Maumee River watershed, are critical in the recent years. In this study, a new BMP cost tool was developed. Then the Soil and Water Assessment Tool (SWAT) and the new BMP cost tool were integrated to explore efficiencies and cost-effectiveness of BMPs in an agricultural catchment of the Maumee River watershed with various scenarios. The scenarios included individual BMPs applied in 100% of suitable areas, individual BMPs targeting Dissolved Reactive Phosphorus (DRP) and Total Phosphorus (TP) critical areas, and BMPs implemented in series. In addition, a cost-effective approach for the selections and placements of BMPs in agricultural watersheds was developed as an alternative to running complex optimization tools that are not applicable to large watersheds. The cost-effective approach applied BMPs based on cost-effectiveness rankings starting from the most cost-effective one. Results showed that: (1) BMPs implemented in series, which reduced pollutant loads more than individual BMPs, were not as cost-effective as some individual BMPs; (2) among all scenarios, filter strips targeting DRP/TP critical areas were the most cost-effective in reducing yearly/spring DRP/TP losses; (3) to obtain the watershed management plan goal of reducing March-July DRP/TP losses by 40%, implementing BMPs one by one in critical areas based on the cost-effectiveness rankings of individual BMPs in DRP/TP critical areas was the most cost-effective; and (4) the simulation results, modeling tools, and cost-effective approach can help create agricultural BMP strategies to cost-efficiently improve water quality.