Macrozoobenthos variations in shallow connected lakes under the influence of intense hydrologic pulse changes

Abstract Hydrologic pulse represent one of the dominant factors controlling the distribution of aquatic organisms. Changes in hydrologic pulses may change the surroundings of the organism and then affect their distribution and community structure. Here, based on the data from a rainy season and a dry season, the water quality, heavy metal in the sediment and macrozoobenthos community structure in two shallow lakes, Nansihu Lake (NSH) and Dongpinghu Lake (DPH, were analyzed. The results showed that the water diversion pulse participated in the influence of runoff pulse on NSH and DPH. The macrozoobenthos community in NSH and DPH were similar after the hydrologic pulse changed, this might be due to these two lakes were connected by the South-to-North Water Transfer Project (SNWTP). Along the direction of water transfer, the macrozoobenthos communities were gradually dominated by small-size species with as water quality decreased. Compared with community structure before the SNWTP, the macrozoobenthos changed from dominant aquatic insect to dominant Mollusca in NSH, and changed from dominant Mollusca and Oligochaeta to dominant Mollusca in DPH. The water diversion pulse, in which the direction of water transfer was opposite to that of natural water flow, affected the distribution of nitrogen and phosphorous in water and heavy metals in sediment. In addition, the introduction of exogenous water caused by the SNWTP changed water quality and heavy metals content in the sediment and water depth in NSH and DPH. These changes together affected the community structure and distribution of macrozoobenthos. These findings enable a better understanding of the ecological impact of intense hydrologic pulse changes caused by water transfer projects.