Rainfall-runoff duration shapes divergent water quality and microbial assembly patterns in a drinking water reservoir

Under climate change, the frequency of extreme rainfall events is increasing. However, how rainfall-runoff duration shapes water quality dynamics and microbial ecological processes in drinking water reservoirs remains poorly understood. Using Jinpen Reservoir as a case study, this study investigated ecological responses to contrasting short- and long-duration rainfall-runoff events by integrating water quality monitoring, microbial community analysis, community assembly assessment, and functional potential prediction. Short-duration rainfall-runoff resulted in rapid pulse inputs of allochthonous nutrients and organic matter, leading to transient deterioration of water quality. In contrast, long-duration continuous rainfall-runoff promoted enhanced water renewal and vertical mixing, coinciding with improved water quality conditions during the later stage of the event. Microbial communities exhibited distinct response patterns under contrasting rainfall-runoff regimes. Short-duration rainfall-runoff induced transient microbial community fluctuations and maintained higher community evenness, whereas long-duration rainfall-runoff was linked to persistent microbial community reorganization, altered microbial association networks, increased community richness, a higher proportion of specialist taxa, and stronger environmental filtering signals. Redundancy analysis (RDA) and Mantel tests revealed that nitrogen, phosphorus, dissolved organic carbon (DOC), CODMn, and turbidity were key environmental factors associated with microbial community variation. PICRUSt2-based functional prediction further indicated that long-duration rainfall-runoff was linked to enhanced predicted microbial functional potential, particularly for nitrogen cycling-related functional pathways. Overall, this study reveals that rainfall-runoff events with different durations correspond to distinct ecological response modes, with prolonged disturbances associated with stronger environmental coupling and microbial community reorganization. These findings advance our understanding of reservoir microbial responses under changing precipitation regimes and provide scientific insights for adaptive management of drinking water reservoirs under climate change.