Abstract: Accurately estimating non-point source pollution load is crucial for developing a standard-meeting water quality plan for the Yanghua River. By employing an improved output coefficient method, we estimated the total non-point source pollution load of Yanghua River small watershed, which is a tributary of the Tuojiang River. In consideration of the proportion of monthly rainfall in annual rainfall, we can obtain the refined estimation data of monthly distribution of non-point source pollution load. Our findings indicate that COD pollution in the watershed was most severe in 2020, with a total pollution load of 6 042.61 t, primarily concentrated in Zhuanlong Town, Zhugao Town, Hefeng Town, Yunlong Town, and Shijia Town. Non-point sources such as rural dispersed areas and large-scale livestock and poultry farming contributed significantly to pollutants such as COD, ammonia nitrogen, and total phosphorus. Additionally, we successfully obtained the preliminary monthly distribution of non-point source pollution load within the year. These results demonstrated good agreement with measured data, with an average error less than 10%. Overall, our research outcomes provide essential data support for the refined management of water environment in the basin.

Key words: estimation of non-point source pollution, pollution load distribution, improved export coefficient method, Yanghua River Basin