Linking hydraulic geometry, land use, and stream water quality in the Taihu Basin, China

Understanding the complexity of catchment-scale human activities, natural factors, and stream water quality is particularly important for basin water resources management. Thorough investigations on how multiple environmental factors quantitatively and simultaneously affect water quality are limited. This study employed Spearman's correlation and ridge regression analysis (RRA) to disentangle the hydraulic geometry and land use contributions to water quality variables (WQVs). Nine and six indicators were used to describe the hydraulic geometry and land use characteristics, respectively, in the Taihu Basin. The results revealed significant correlations between the land use, hydraulic geometry, and stream water quality. Built-up land and cropland negatively impacted the stream water quality, while woodland had the opposite trend. The structure and morphological connectivity of the river network were associated with most WQVs. The hydrologic connectivity characteristics strongly influenced ammonia-nitrogen (NH₃-N), permanganate index (COD_Mn), and dissolved oxygen (DO). Six equations that estimated the stream water quality were established through RRA. Human factors impose a greater impact on the stream water quality than natural factors in the Taihu Basin. Our findings provide quantitative insights to mitigate water pollution via reasonable management and control of the river structure and connectivity and land-use patterns.