Effect of hydrological regime on the macroinvertebrate community in Three-Gorges Reservoir, China

Dam construction resulting from river closure always leads to dramatic changes of the hydrological conditions and influences the aquatic ecosystems seriously. The response of the macroinvertebrate community during the 5 years (2 impoundment stages) after the impoundment of Three-Gorges Reservoir (TGR) was analyzed to illustrate the difference of the macroinvertebrate communities between the two stages after impoundment, indicating the hydrological effects on the aquatic ecosystem. The results showed that the total density of macroinvertebrates increased significantly, and displayed obvious seasonal patterns, after more than one year's ecosystem rebuilding. Density after the second impoundment did not show a significant difference compared to that of the two years before the second impoundment. The maximum value appeared in spring, with naididae dominating the community (relative abundance over 90%). Shannon-Wiener diversity index also displayed obvious seasonal fluctuations with the maximum value in winter and minimum in autumn. The NMS ordination to the macroinvertebrate community indicated the seasonal patterns have become relatively stable from 2005 in the first stage, except the autumn. After the second impoundment, the seasonal patterns became more stable, and even the macroinvertebrates in the autumn, when the impoundment plan was carried out, were also similar. The correlation analysis between the hydrological factors and the macroinvertebrate parameters showed that the effect of the hydrological regime began to be significant from 2005. The inflow discharge caused positive effects on tubificidae, but negative ones on naididae. Relatively high transparency was more beneficial to the survival of the naididae. Additionally, the water residence time appeared significant influence to the Shannon-Wiener diversity.