Impacts of different types of wastewater discharge on plankton community structure in the receiving rivers of the Yangtze River

The quantities of industrial and domestic wastewater are increasing in the Yangtze River Basin, which may have a significant impact on receiving rivers. Many studies have examined plankton distribution patterns influenced by wastewater treatment plant (WWTP) effluents. However, few have explored how different wastewaters (domestic, industrial, and mixed) affect plankton communities. To address this gap, 92 samples were collected from the receiving rivers within the Yangtze River Basin during various seasons. The results showed that the treated industrial wastewater significantly altered the plankton community structure via elevated salinity, particularly affecting phytoplankton seasonal variation. Phytoplankton numbers during the dry season were more than 10 % higher than those during the wet season, in contrast to trends from other wastewaters. Both plankton (specifically for Bacillariophyta) density and biomass decreased by approximately 36 % following the input of treated wastewater, but increased again 500 m downstream of outfall in both seasons. Industrial wastewater samples exhibited stronger connections among higher taxa and more negative associations between F^-, TDS, Cl^-, K⁺, Na⁺, etc., with various species than those influenced by other wastewaters. Furthermore, ecosystem health levels gradually improved from poor status near the outfall to sub-health status 10 km downstream of the confluence with the mainstream. These findings reveal the impacts of different types of wastewater on plankton communities. Incorporating salinity into regulatory assessment criteria and optimize treatment processes to reduce effluent salinity. This study provides critical guidance into the effects of wastewater discharge on freshwater ecosystem functioning.