Evaluation of long-term water quality trends and CCME-WQI applicability in agricultural watersheds of Korea

This study analyzed 10-year (2015 -2024) trends in water quality parameters and the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI) across five provinces in Korea.The CCME-WQI analysis indicated that Gangwon-do maintained Fair to Good ratings with high stability, while Gyeonggi-do generally fell within the Marginal range.Chungcheong-do showed persistently low water quality, mostly within the Poor range.Jeolla-do exhibited mostly Poor-level quality, and Gyeongsang-do showed moderate variability with Fair-level quality overall.The nationwide average CCME-WQI was approximately 55.7, indicating a marginal water quality level overall.The coefficient of variation (CV) for CCME-WQI was consistently lower than that of individual parameters, supporting its robustness and representativeness as an integrated indicator.Correlation analysis revealed strong positive relationships between farmland ratio and nutrient-related indicators (e.g., COD Mn , T-P, SS), and significant negative correlations between CCME-WQI and these pollutants (e.g., SS: r = -0.96).Additionally, cumulative precipitation-particularly in Julyshowed stronger negative correlations with CCME-WQI (e.g., July: r = -0.80)than the farmland ratio (r = -0.69),suggesting that hydrological variability may exert a more immediate influence on water quality in agricultural watersheds than static land use patterns.These findings suggest that CCME-WQI is an effective tool for long-term water quality evaluation in agricultural watersheds influenced by non-point source pollution.