Characteristics of phytoplankton and macrozoobenthos communities in Nansihu Lake under the influence of hydrologic pulse

The hydrologic pulse affects lake water ecosystem, complicated further by hydrologic pulse due to the South to North Water Transfer Project (SNWTP). Phytoplankton and macrozoobenthos in Nansihu Lake (NSH) during non-diversion period and diversion period were investigated. Water quality and heavy metals in the sediment, characteristics of phytoplankton and macrozoobenthos communities under influence of hydrologic pulse by SNWTP were analyzed. During a whole pulse period, total phytoplankton density was found to have decreased, proportion of Cyanophyta decreased, proportion of Chlorophyta and Bacillaroiphyta increased, with dominant species having changed dramatically. Macrozoobenthos community in NSH mainly included Mollusca, aquatic insects and aquatic oligochaetes, dominated by Mollusca. The community structure of macrozoobenthos was stable, dominant species turnover was weak, diversity index did not change. Compared with before implementation of SNWTP, phytoplankton community in NSH changed more significantly during a year, diversity index decreased. With water quality getting better and heavy metal distribution in sediment changing, macrozoobenthos gradually changed from that dominated by small-size aquatic insects to that dominated by large-size Mollusca. These indicate that effects of hydrologic pulse caused by SNWTP on phytoplankton are obvious in both short and long term and more obvious in the long-term cumulative effects on macrozoobenthos.