Multi-Model Approaches Reveal Cascading Regulation and Ecological Responses of Zooplankton to Seasonal and Water Quality Variations in Urbanized Rivers

Urbanization imposes multiple environmental stressors on urban rivers. Zooplankton are sensitive to environmental disturbances, making them useful tools for assessing ecological health and revealing river degradation processes. We surveyed the urban reaches of the middle and lower Jialing River and its tributary (Xichong River) during autumn 2022 and spring 2023. Water ecological status was assessed using the water quality index and zooplankton-based Index of Biotic Integrity. Community assembly mechanisms and their driving pathways were analyzed by combining the neutral community model (NCM, MST), random forest (RF), and partial least squares path modeling (PLS-PM). Key results: (1) The zooplankton community in the Jialing River Basin exhibited significant spatiotemporal heterogeneity. (2) The overall water ecological status was better in the mainstream than in the tributary, and better in autumn than in spring. (3) Stochastic processes dominated the Jialing River mainstream in autumn (MST = 0.5388), whereas deterministic processes dominated in all other habitats. (4) Seasonal variation was the key driver of community assembly (R2 = 0.253, p < 0.001), and CODMn was the primary water quality factor (IncMSE = 25.48%). In summary, multiple models combined quantified the dominant pathways of ecological response, providing theoretical support for the health management of urbanized rivers.