New framework for nonpoint source pollution management based on downscaling priority management areas

Abstract

Scale transformation is a problem in many fields, especially in geoscience. But there is less report on the use of scale transformation to control non-point source (NPS) pollution. This study constructs a new framework for NPS pollution management by re-downscaling pollution source area and exploring the effects of Best Management Practices (BMPs) on water quality improvement at large scale after treatment of small-scale subwatersheds. Combined with Soil and Water Assessment Tool (SWAT), the advantage and uncertainty of the framework were explored though a case study in the Three Gorges Reservoir Region, China. Based on the results, the framework improved the efficiency of priority management areas (PMAs) identification. After the re-downscaling the PMAs, the total phosphorus (TP) load intensity increased from 59.3 kg/km2 to 84.3 kg/km2 for those high-ranking PMAs, while the area of PMAs with the maximum intensity increased by 4.44%. The framework has the most obvious advantages when the TP reduction target is set as 38.00%. The NPS management area after re-downscaling would reduce by 2.46% compare to primary PMAs. Water quality target, assessment points and hydrological periods are identified as the uncertain factors. The selection of proper water quality target and the assessment point would account for 19.03% and 10.61% reduction of NPS control area. From dry to wet years, the NPS control area increased by 647 km2 which accounts for 26.71% of the watershed, while the maximum intensity changed from 27.6 kg/km2 to 59.3 kg/km2. The new framework can be extended to other watersheds for the NPS management at watershed scale.