Effect of flow-sediment regime on benthic invertebrate communities: Long-term analysis in a regulated floodplain lake

Flow and sediment co-create habitat structure and dynamics within river and lake systems, of which the ecological effects are well-documented. But the temporal variability of aquatic community response to continuous flow-sediment alterations is less well-known. This paper explored aquatic biota response to the flow-sediment regime in a broader temporal context using long-term paired hydrological database and monitoring data of benthic invertebrates in Dongting Lake. The inter-annual variations of benthic invertebrates and certain flow and sediment variables were synchronous. Community diversity parameters showed different response to different hydrological events and particularly revealed a short-term peak in the first two years after the operation of the Three Gorges Dam. This finding affirmed the importance of the time series study. The overall flow-sediment regime, calculated from 15 flow and sediment characteristics, affected community structures and could also affect benthic invertebrates by affecting the water quality. The combination of variables, including sediment inputs load, sediment exports/inputs ratio and the duration of low water level, could best explain the variation of benthic invertebrate assemblages and should be given the greatest management concern. When individual components of the flow-sediment regime were analysed, the response patterns of community parameters to different environmental variables or to different gradients of the same variables were complex. Our results suggest that the sediment seemed to be a more influential stressor than flow, especially erosion, which could significantly reduce total abundance and species richness. The effect of the flow regime was reflected by the duration of the low water level. Stressor gradients and the response patterns of different taxa to different stressors should be considered by river and lake managers. The results would provide valuable information for the design of lake management strategies and upstream reservoir regulation rules.