Phytoplankton Community Structure And Its Relationship With Environmental Factors In Liangzihu Lake

Liangzihu Lake is a typical shallow macrophytic lake in the middle reach of Yangtze River in Hubei Province, China. It is one of the few lakes that selected as a pilot lake in ecological environmental protection, and plays a very important role in irrigation, shipping, tourism, and drainage and some other aspects. A study about its phytoplankton community in relation to physicochemical factors was performed from January, 2012 to December, 2012 in Liangzihu Lake. The results of the study are as follows:(1) A total of 8 phylums, 109 genera, 317 species of phytoplankton were identified during the whole year investigation, Chlorophyta, Bacillariophyta and Cyanophyta were the main phylums. Summer>spring>autumn>winter were the temporal characteristics of the total phytoplankton species numbers, for spatial characteristics, Cyanophyta and Bacillariophyta were the main composition of phytoplankton in the west of Liangzihu Lake and Cyanophyta, Bacillariophyta and Cryptophyta in east of the lake. The mean density of phytoplankton was 39.07 cell/L×105 cell/L and the variation range was 4.61×105 cell/L~114.47×105 cell/L. For seasonal changes of phytoplankton density, it was highest in summer, followed by autumn, winter and spring. For spatial changes, it was higher in the west of Liangzihu Lake and lower in east of the lake. The mean biomass of phytoplankton was 4.27 mg/L and the variation range was 0.37 mg/L~11.03 mg/L. For seasonal changes of phytoplankton biomass, it was highest in summer, followed by autumn, winter and spring. For spatial changes, it was high in the west of Liangzihu Lake and low in east of the lake.(2) The phytoplankton dominant species during the whole sampling period were Ankistrodesmus convolutes, Melosiragranulate, Melosira granulata var. angustissima, Oscillatoria amphibian, Cryptomonas erosa, and Raphidiopsis curvata. For seasonal changes, the main dominant species in spring were Dinobryon divergens, Ankistrodesmus, Cryptomonas erosa, in summer were Melosira, Oscillatoria, and Phormidium, in autumn were Raphidiopsis curvata, Ankistrodesmus convolutes, and Melosira granulate, and in winter were Ankistrodesmus, Aphanocapsa, Oscillatoria, Melosira, and Dinobryon. For spatial changes, the major domiant species in the west of Liangzihu Lake was Raphidiopsis curvata, and Cryptomonas erosa was the main dominant species in east of the lake.(3) The annual mean value of Margalef index(D), Shannon-Weaver index(H’) and Pielou index(J) were 4.99, 3.40 and 0.80, respectively. For seasonal changes, the three kinds of diversity indexes were all highest in summer, followed by spring, autumn and winter. For spatial changes, the three kinds of diversity indexes were all higher in the east of Liangzihu Lake than in west of the lake.(4) The annual mean dissolved oxygen was 9.91 mg/L, p H was 8.36, permanganate index was 3.20 mg/L, ammonia nitrogen was 0.018 mg/L, nitrite nitrogen was 0.007 mg/L, nitrate nitrogen was 0.256 mg/L, total nitrogen was 0.679 mg/L, orthophosphate phosphorus was 0.012 mg/L, total phosphorus was 0.037 mg/L, and TN/TP was 18.7.(5) The water trophic status in Liangzihu Lake was the transitional state between mesotrophic type to eutrophic type, and the water pollution degree belonged to the transitional state between light pollution and moderate pollution, combined biological index with physicochemical index evaluation methods.(6) SPSS correlation analysis indicated that phytoplankton density and biomass were positive correlated to water depth, water temperature, p H and negative to transparency, dissolved oxygen, nitrite nitrogen, nitrate nitrogen, significantly(P<0.05). RDA analysis indicated that total nitrogen, transparency, permanganate index were the main indicators that affected phytoplankton in summer in Liangzihu Lake, and total phosphorus and permanganate index in autumn.