Decoupling of diversity and network complexity of bacterial communities during water quality deterioration

Numerous studies have examined the impact of water quality degradation on bacterial community structure, yet insights into its effects on the bacterial ecological networks remain scarce. In this study, we investigated the diversity, composition, assembly patterns, ecological networks, and environmental determinants of bacterial communities across 20 ponds to understand the impact of water quality degradation. Our findings revealed that water quality degradation significantly reduces the α-diversity of bacterial communities in water samples, while sediment samples remain unaffected. Additionally, water quality deterioration increases the complexity of bacterial networks in water samples but reduces it in sediment samples. These shifts in bacterial communities were primarily governed by deterministic processes, with heterogeneous selection being particularly influential. Through redundancy analysis (RDA), multiple regression on matrices (MRM), and Mantel tests, we identified dissolved oxygen (DO), ammonium nitrogen (NH₄⁺-N), and C/N ratio as key factors affecting the composition and network complexity of bacterial communities in both water and sediment. Overall, this study contributes a novel perspective on the effect of water quality deterioration on microbial ecosystems and provides valuable insights for improving ecological evaluations and biomonitoring practices related to water quality management.