Seasonal management of multiple stressors: Interactive effects of dams and urbanization on pollution loads in the Shaying River Basin, eastern China

Abstract

With population growth and accelerating urbanization in developing regions, numerous dams have been built to support industrial activities and residential water supply. These developments have exposed rivers to the multiple stressors of dams and urbanization, complicating river restoration and water quality predictions. Understanding of how these stressors interact to influence water quality is crucial for effective river management. Therefore, during the wet and dry seasons, we investigated pollutant concentrations (including EC, COD, TN, NH3-N, and TP) and habitat quality in four river systems across different stressor combinations of dam presence/absence and high- or low-intensity urbanization. The findings suggested that the interaction between dams and urbanization exerted additive effect on pollution load (PL) in the wet season and synergistic effect in the dry season. The generalized linear model (GLM) and structural equation modeling (SEM) results revealed that in the wet season, PL was directly influenced by both dams and urbanization, whereas in the dry season, they were driven indirectly by habitat degradation and directly by urbanization. The results of distance-based redundancy analysis (db-RDA) and variation partitioning analysis (VPA) revealed that the interactive effects contributed more to the variation in the structure of water quality parameters (WQPs) in the dry season (27.9 %) than in the wet season (11.3 %). Moreover, in the wet season, PL in the dam group increased gradually from upstream to downstream, whereas in the dry season, an increase occurred in the urban group. Dam elements (flood control and power generation) explained most of variance (29.7 %) in the WQPs in the wet season, whereas urbanization elements (nightlight intensity and land use index) explained most of the variance (33.8 %) in the dry season. It is recommended that in the wet season, dams should be collectively regulated to prevent pollutant migration via flood discharge, whereas in the dry season, efforts should focus on restoring riparian habitats and reducing urban point source pollution.