Study on the delineation method of riverine water source protection zones in the Qujiang River Basin

【Background】River-type water sources are widely distributed in China and serve as the primary source of drinking water. Over the past decades, the proportion of non-compliant water sources has decreased due to effective control of point-source pollution. However, this trend has slowed in recent years, with non-point source pollution increasingly affecting water quality. Current protection methods mainly rely on empirical analogies, making it difficult to quantitatively delineate protection zones for non-point source pollution.【Objective】This study proposes a novel method for delineating water source protection zones that quantitatively accounts for the impacts of non-point source pollution, addressing the limitations of existing approaches in accurately reflecting such influences.【Method】Based on hydrological modeling, this method integrates geographic and ecological attributes to establish a refined framework for delineation. The SWAT model, coupled with the export coefficient method and an improved inverse distance weighting interpolation method, was employed to calculate terrestrial pollutant loads entering water bodies. Natural background conditions were incorporated into the assessment of terrestrial pollutant input. A terrestrial protection zone delineation formula was applied, and further adjustments were made by cross-verifying with topographic profiles.【Result】① The re-delineation of the water source protection zones using the proposed method resulted in a 5% reduction in pollutant load across different protection levels compared to the original zoning.② All protection zones, which previously exceeded standards, now comply with water quality standards, showing improved accuracy and reasonability.【Conclusion】By effectively quantifying the influence of non-point source pollution on protection zone boundaries, the proposed method significantly enhances the precision and applicability of water source protection zoning. The findings highlight the high suitability of this approach for the Qujiang River Basin and its potential to inform pollution prevention and protection zone delineation across China.