This study aimed to derive major pollutants for standard watersheds with relatively high pollution levels and identify their trends. Hence, the water quality index (WQI) and multivariate statistical techniques were used to analyze the water quality evaluation of standard watershed during the total maximum daily load (TMDL) policy period implemented since 2004. The WQI was calculated for 41 standard watersheds, divided into 14 main streams and 27 tributaries. Consequently, in the main stream, WQI decreased as it moved downstream after the MS5 site. In the tributary, WQI values were found to be low at TS11, TS15, TS16, and TS17 sites. However, the Mann–Kendall test results indicated that the overall WQI value was increasing, suggesting that the water quality of the study basin was improving as the TMDL policy phase progressed. Principal component analysis of the group with relatively low WQI among the standard watersheds revealed that water temperature, dissolved oxygen, total phosphorus, chemical oxygen demand, biochemical oxygen demand, and electrical conductivity were the main variables in the main stream cluster. In the tributary stream cluster, total phosphorus, dissolved oxygen, total suspended solids, total nitrogen, and electrical conductivity showed high loading values. This study proposed a series of methods to provide the basic data required for watershed management through detailed water quality assessment methods, statistical techniques for deriving major pollutants, and trend analysis of water quality evaluation.

本研究旨在推导污染水平相对较高的标准流域的主要污染物并确定其趋势。为此，采用水质指数（WQI）和多元统计技术，对2004年以来实施的最大日负荷（TMDL）政策期间标准流域的水质评价进行了分析。计算了41个标准流域的WQI，分为：干流14条，支流27条。因此，在干流中，WQI随着MS5站点之后向下游移动而下降。在支流中，TS11、TS15、TS16 和 TS17 站点的 WQI 值较低。然而，Mann-Kendall 测试结果表明，总体 WQI 值正在增加，表明随着 TMDL 政策阶段的进展，研究流域的水质正在改善。对标准流域中WQI较低组的主成分分析显示，水温、溶解氧、总磷、化学需氧量、生化需氧量和电导率是干流簇中的主要变量。在支流簇中，总磷、溶解氧、总悬浮固体、总氮和电导率均显示出较高的负荷值。本研究提出了一系列方法，通过详细的水质评价方法、主要污染物统计技术以及水质评价趋势分析，为流域管理提供所需的基础数据。