Water Quality Assessment and Driving Mechanism Analysis of the Hanjiang River Basin Based on WQI-PCA-OPGD

• • TN was the most severe pollutant, with concentrations exceeding the Class III standard (1.0 mg/L) in over 60% of sections during the study period, hindering overall water quality improvement. • • WQI values ranged from 20.5 to 91.3 across sections, with 78% of sections classified as 'good' or better, but 12% of sections in downstream tributaries fell into 'poor' category, indicating localized pollution hotspots. • • PCA identified two principal components explaining 68.4% of variance: PC1 (organic pollution) and PC2 (nutrient pollution), with PC1 dominant in dry season and PC2 in wet season. • • OPGD analysis showed that land use type (q=0.42) and elevation (q=0.38) were the dominant factors, with interactions between natural and anthropogenic factors explaining up to 0.65 of water quality variance, underscoring the need for integrated management.