Study On The Variation Characteristics Of Dominant Species Of Phytoplankton Community In Dianshan Lake

In order to evaluate the spatial and temporal distribution of phytoplankton community and the dominant phytoplankton species in Dianshan Lake, an investigation was carried out from December2010to November2011. In this period,23sampling sites were selected and the samples were run once a month. The species composition, density variation, dominant species, the niche breadths and niche overlaps of dominant phytoplankton species were comprehensively studied. The main results are as follows:1. The phytoplankton in the Dianshan Lake was composed of373species belonging to8phylum and127genera (with varietas and metatype). The phytoplankton community was mainly composed of Chlorophyta (60genera153species), Bacillariophyta (29genera93species). Cycmophylu (13genera39species), Euglenophyta (7genera45species), Cryptophyta (3genera9species), Chrysophyta (9genera23species), Xanthophyceae (4genera8species), Pyrrophyta (2genera6species). The density of different phylum from high to low was Chlorophyta, Cryptophyta, Bacillariophyta, Cyanophyta, Euglenophyta, Chrysophyta, Xanthophyceae and Pyrrophyta. A total of6phylum,34species of phytoplankton were identified (with varietas and metatype), Chlorophyta and Bacillariophyta were the main group of dominant species. Chlorella vulgaris, Chroomonas acuta and Melosira varians were the dominate species all year round.2. The seasonal order of phytoplankton species number from high to low was summer, spring, autumn, winter, while the spatial order was north, west, southwest, middle of the lake, south and east. The phytoplankton density was on average1.23×107cells·L-1with double peaks in a year. Moreover, the spring peak was much higher than that in summer. The seasonal order of phytoplankton density from high to low was spring, summer, autumn, winter, while the spatial order was north, west, south, middle of the lake, east and southwest.3. The variation orderliness of community structure of phytoplankton was as followed:Cyanophyta-Chlorophyta type in winter, Cryptophyta-Bacillariophyta type in spring, Cyanophyta-Cryptophyta-Bacillariophyta type in summer, Cryptophyta type in autumn. There are both similarity and difference of dominant species in different month and an obvious succession of phytoplankton species is found. As the dominate species, Chlorella vulgaris, Chroomonas acuta and Melosira varians were appear in every month. Changes of the densities of dominant species have strong relevance to the changes of the total density of phytoplankton community. The main genera of the dominant species were Chlorella、Chroomonas、Cryptomonas and Melosira in different sampling sites, while the species number in north sites are higher than other sites. The sampling sites in the middle and the outlet area of the lake have more significant differences in dominant species at different depth.4. Hierarchical Cluster Analysis showed that, the sites near the lakeside, in the middle and the outlet area of Dianshan Lake have more significant differences within the species and the densities of phytoplankton community compare to the other sampling sites in four seasons. There was an obvious succession change of phytoplankton community in north area in different month, while an alternate change in south area; In the west and the east area, the differences of the phytoplankton among these sites were evident, while in the middle and the outlet area, the differences were unobvious. There was an quickly replace of dominant species in winter and spring, and the species number have larger difference at different depth among the sites in the middle and the outlet area.5. The niche breadths and niche overlaps of the dominant species were dissimilar in different periods, which showed that different dominant species have different adaptive capacity to the environmental factors. These dominant species of Dianshan Lake can be divided into five groups based on niche breadth. Chroomonas acula and Chlorella vulgaris have broader niche, more quantities, and wider distributions and make better use of environmental resources; the species have narrow niche become dominant species in mostly months or with less wide distributions; other species have no wide or no narrow niche. The niche overlaps among Lyngbya limnetica, Melosira ambigua and other dominant species were comparatively higher. Melosira varians and Lyngbya limnetica were belong to the developing species, and have much more developing spaces, while the Chlorella vulgaris and Chroomonas acuta showed a decline status. Correlation analysis among density, dominance, niche breadth and niche overlaps showed that density and dominance of dominant species had strong relevance to the niche breadths, while there were no significant correlation among density and dominance of dominant species and the niche overlaps.6. Evaluation results of dominant species showed the water in Dianshan Lake was Mesotrophication-Eutrophication. The degree of eutrophication changed with seasonal variation. It was higher in summer, then spring, autumn and winter were lower. The evaluation results of pollution monitoring species also showed the water in Dianshan Lake was Mesotrophication-Eutrophication. The degree of eutrophication from high to low were spring, summer, autumn, winter. East area were higher, the other sites were relatively lower. Evaluation results compare to three indexes showed the degree of eutrophication within different areas, from high to low which were east, then southwest and west, the degree of eutrophication in other areas were lower.