Studies On Zooplankton Community Structure And Their Relationships With Environmental Conditions In Liangzi Lake

Liangzi Lake is a shallow macrophtic lake along the middle and lower reaches of the Yangtze River. The studied region includes Gaotang Lake, Qianjiangda Lake and Manjiang Lake, which is divided into three parts by the Liangzi Island. So many lake branches lead to the difficult water exchange and mix, make the composition and characteristics of zooplankton community structure and nutritional status varied. In this study, species composition, density, biomass, dominant species of zooplankton community and the water environmental factors were investigated throughout the year2012. The temporal and spatial variation of zooplankton community structure and correlations with water environmental factors were analyzed to provide a theoretical foundation and scientific basis for environmental protection and water eutrophication control of Liangzi Lake, and proposes measures to protect and restore the water environment of Liangzi Lake. The results were as follows:(1) There are185species of zooplankton, during the2012survey, including80species of protozoa (including the species of amoebae and ciliates, but not including flagellates),89species of rotifers,13species of cladocerans and3species of copepods. The proportion of rotifers in the zooplankton species composition of each month reached43%-58%and the proportion of protozoa reached32%-46%, which indicates that a small species dominated of zooplankton composition in Liangzi Lake. It was significantly that the species number of protozoa and rotifers were higher in summer and autumn than it in winter and spring, while cladocerans and copepods species number were less and the seasonal trend were not obvious. The zooplankton species number of sampling points in the East Liangzi Lake was higher than Qianjiangda Lake on the spatial distribution. Sampling point1had the minimum number of zooplankton species, but sampling point2had the maximum number of zooplankton species, and the number of zooplankton species gradually reduced from sampling point2to sampling point6along the Gaotang Lake to the north. The species number of zooplankton has returned to a higher level when it reached the sampling point7. There are53dominant species of zooplankton were selected based on the frequency of appearance and dominance of each month in Liangzi lake, of which there are14species of rotifers,24species of protozoa,16species of cladocerans and copepods. (2) The total and annual density of zooplankton varied from811ind./L to21445ind./L. The average of total and annual density was11383ind./L. Total biomass throughout the year varied in0.88-12.54mg/L. The average of annual total biomass was4.55mg/L. The total density of zooplankton of the Liangzi Lake performanced the characteristic that it was high in summer and autumn, but it was low in winter and spring. Density of protozoa and rotifers has the dominant position in total density of zooplankton. The total biomass of Liangzi Lake performanced that it was higher in summer than other seasons, and it was the lowest in spring. Protozoa and rotifers biomass reaches the proportion of3.19%-32.23%of the total biomass, it was visible that cladocerans and copepods biomass is the major component of the total biomass, the biomass of rotifers was followed; the biomass of protozoa was in the lowest proportion. On the whole lake level, the density and biomass of zooplankton in sampling point1was lowest in the East Liangzi Lake. The density and biomass of zooplankton in each sampling point of East Liangzi Lake was higher than Qianjiangda Lake, except for sampling point1.(3) According to the results of Liangzi Lake zooplankton density and water environmental factors CCA (Canonical Correspond Analysis), we found that the water temperature, chlorophyll a concentration, dissolved oxygen, pH, nitrate, total nitrogen, permanganate index and transparency is the main environmental factors affecting zooplankton density variations and it was different because of the different types of zooplankton suitable environmental conditions vary. Therefore, it is necessary to control the upstream and the surrounding point source or non-point source pollution of Liangzi Lake, and put some silver carp and bighead carp and other filter-feeding fish to reduce inner source pollution of Liangzi Lake, even more, raise the coverage of submerged vegetation in Liangzi Lake, to improve the number of zooplankton species, in order to increase the stability of the water ecosystem.