Higher spatial than seasonal variation of microbial communities in long-term reclaimed water headwater urban stream

Revealing the ecological impact of reclaimed water (RW) replenishment on bacterioplankton communities is crucial to promote RW utilization, yet less attention has been paid to the RW headwater urban stream with continuous RW recharge. Here, we collected water samples from Lujia stream to investigate the bacterioplankton community diversity, network, and assembly in spatiotemporal variation. Based on statistical analyses, bacterioplankton diversity in the midstream section was the lowest, especially in the dry season. Furthermore, spatial heterogeneity was more significant than seasonal heterogeneity for both biotic and abiotic factors. Dissolved oxygen and nitrite were the environmental driving factors of the bacterioplankton community in the wet and dry seasons, respectively. Intriguingly, a series of indicator bacteria related to nutrient nitrogen cycling were identified in the midstream section. Meanwhile, co-occurrence network analysis showed that the midstream section had the strongest competitive antagonism. Furthermore, the results of community assembly also showed that the midstream section harbored the highest proportions of stochastic processes, which were obviously different from the two other sections. Consequently, the midstream section was presumed to be a community coalescence area. Overall, our findings not only filled gaps in understanding the characteristics of bacterioplankton communities in long-term RW headwater urban streams but also highlighted the importance of the midstream section as a key objective of river restoration and management.