| Songnen plain is one of the highest density of lakes areas in China, there are plenty of lake and pool group as low plain lake group in the temperate semihumid area. Being the various types of lakes, there are a plenty of hydrophytic plant and animal resources. Algae assemblages were investigated at 82 sampling sites of 32 lakes in Songnen plain from June to August in 2008, and 164 samples were obtained. pH value and water temperature at each site were also measured. The cell density and composition of algae species in different lakes were examined, the diversity of community structure of algae was analyzed by diversity index, and the relationship between algae and environmental factors was analyzed and discussed, and using the research results and data to value water quality. All these studies can provide basic data for the protection of environment and the material of lakes in Songnen plain. The results as follows:1.There are abundant algae in the lakes of Songnen plain, and sum of 237 taxa were found, including Bacillariophyta 28 genera 113 species 16 varieties and 3 forms, Chlorophyta 19 genera 52 species 12 varieties and 1 form, Cyanophyta 9 genera 24 species, Euglenophyta 3 genera 13 species, Dinophyta 2 genera 2 species, Xanthophyta 1 genera 1 species. Based on the quantitative analysis, the total average cell density of algae was 8.71×10~6ind/L, which including 3.98×10~6ind/L Bacillariophyta, 2.22×10~6ind/L Chlorophyta, 1.99×10~6ind/L Cyanophyta, 4.06×10~5ind/L Euglenophyta, 1.07×10~5ind/L Dinophyta, 1.34×10~4ind/L Xanthophyta. Comparing with other algae, Bacillariophyta was the major in the species composition and amount of algae, followed by Chlorophyta. The community composition of algae might be classified as Bacillariophyta- Chlorophyta type in Songnen plain.2. Comparing the community structure of algae in different lakes showed that the character of the algae distribution from the lakes in Songnen plain was provided with less taxa and more abundance. All the dominant species in different lakes were counted, Melosira granulata, Melosira ambigua and Cyclotella meneghiniana can be used as indicator species throughout the studied area, being salt tolerance to some degree and growing in eutrophic water. Other dominant species such as Cymbella cistula and Scenedesmus bijuga were found in a small number of lakes. 3. Margalef index, Shannon-Wieaver index, Pielou index, Simpson index and Diversity threshold index were comprehensively used, the range of H value was 0.193 to 1.651, the range of H' value was 1.157 to 2.999, the range of J value was 0.737 to 0.976, the range of D value was 0.627 to 0.937 and the range of Dv value was 1.386 to 3.332. The analysis showed that water nutrition was mesotrophic basically in studied area.4. Taking Chagan Lake (CGH) and Moon Lake as examples, the spatial difference of algae community structure in a lake was researched by using Jaccard similarity index (X). The results showed that the eco-environment of Chagan Lake at CGH-1 was similar to that at CGH-2, CGH-3, CGH-4 and CGH-5, of which, the eco-environment at CGH-1 was most similar to that at CGH-2 and CGH-3, the eco-environment at CGH-6 was similar to that at CGH-7 at CGH-8; The eco-environment of Moon Lake at YLP-1 was similar to that at YLP-2 and YLP-4, the eco-environment at YLP-5 was similar to that at YLP-6, the eco-environment at YLP-3 was less similar to that in other sampling sites. Meanwhile, the characteristic of algae community structure in different sampling sites of the two lakes was consistent with the result measured by Jaccard similarity index.5. The range of temperature in 32 lakes was 20.86℃to 29.35℃, and the average temperature was 24.96℃, the great majority of algae discovered from all sampling sites were wide temperature taxa, meanwhile, there were a small amount of cold water taxa and warm water taxa. The range of pH value in 32 lakes was 7.07 to 9.47,and the average pH value was 8.86, most of taxa sampled from 32 lakes were alkalibiontic, only a few neutral and acidobiontic taxa were found; Some taxa also found in lakes, ponds and standing water. A large number of taxa found in studied area were cosmopolitan, and some taxa which often exist in brackish water or salt water were also reported. The distribution of these taxa was consistent with the environmental characteristics of sampling sites.6. Using bio-directed method of the algae, the types and degree of the pollution of water quality were preliminary evaluated. The great majority of taxa from 32 lakes belong toβ-mesosaprobic zone indicators, and the dominant species existed in most of 32 lakes were alsoβ-mesosaprobic zone indicators, this showed that the water quality belong toβ-mesosaprobic zone in Songnen plain. In addition, few of industrial toxicology indicators of algae were found in some of the lakes.
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