Phytoplankton Community Structure And Analysis Of Correlations With Environmental Factors In Xiaoxingkai Lake

The national "Twelfth Five-Year Plan" clearly put forward to strengthen prevention and cure about pollution of the cross-border river and lake. As the Sino-Russian border lake, Xingkai Lake is the largest freshwater lake in land border area of China. The geographical position of Xiaoxingkai Lake is very important, which has hydraulic connection with the Daxingkai Lake. They are only separated by a dam, so their water ecosystem’s state of health needs to be carried on monitoring effectively. The research established12typical sampling stations according to the topography and the surrounding environment in Xiaoxingkai Lake, and samplings were done once a month from May to September in2011. Qualitative and quantitative investigations were conducted to the phytoplankton of samplings, and simultaneously the corresponding water environmental factors were monitored and analyzed. Multivariate statistical method was used to analyze phytoplankton’s biodiversity and the community structure. The correlation between phytoplankton and environmental factors was determined by Pearson analysis. The research could provide scientific basis for the protection and management of Xiaoxingkai Lake Basin.A total of7phyla,121species were identified in Xiaoxingkai Lake, including Cyanophyta, Chlorophyta, Bacillariophyta, Pyrrophyta, Cryptophyta, Euglenophyta and Chrysophyta. Among which, the majority were bacillariophyta (53species), Chlorophyta (32species), Cyanophyta (27species), and the other9species were also identified. Temporal distribution of species richness of phytoplankton was obvious, the most (82species) occured in July, and the least (56species) occured in September. On the spatial distribution, species richness was the most (64species) at Xinkaoliu (1#) which had water exchange with Daxingkai Lake, and it was the least (41species) at Paoshulinzi (10#) which was near the farmlands. A total of16dominant species was found. The number of dominant phytoplankton species was the least in June, while its dominant degree was high. The number of dominant species was the most in September, and its dominant degree was low. The major phytoplankton compositions were bacillariophyta, Chlorophyta and Cyanophyta throughout the year.The temporal and spatial non-uniformity of phytoplankton’s abundance and biomass were remarkable in Xiaoxingkai Lake. On the temporal distribution, the highest abundance and biomass were in July, the lowest abundance was in September and the lowest biomass was in June. On the spatial distribution, the abundance and biomass at Erzha (7#) which had water exchange with Daxingkai Lake was the highest, the lowest abundance was in the center of the lake (3#), and the lowest biomass was at West Pier (11#) which was disturbed by the residential area. The abundance and biomass in the areas which had water exchange were significantly higher than other areas.Temporal and spatial distributions of phytoplankton’s biodiversity indexes were remarkable in Xiaoxingkai Lake. The Shannon-Wiener index was2.64-4.64, the Margalef index was1.46-5.17, and Pielou index was0.35-0.86during the whole year. The Shannon-Wiener index and Margalef index were highest in May, and they were the lowest in September; the Pielou index was highest in September, and it was the lowest in July. The diversity index in the undisturbed areas was significantly higher than the areas which were affected by human activities in Xiaoxingkai Lake. Overall, the whole lake was mesotrophic-eutrophic.According to the analysis of environmental factors, we found that phytoplankton’s abundance and biomass had close relation with environmental factors such as chlorophyll a, dissolved oxygen (DO), chemical oxygen demand (COD),TN, TP and soluble iron and so on. The environmental factors’distribution have obvious temporal and spatial characteristics. And the relation between the phytoplankton’s growth and each environmental factor was different in each month. The major physical-chemical factors which affect the growth of phytoplankton were chlorophyll a, water depth and transparency. On the temporal distribution, the highest TN value was in June, and the least was in July; the highest TP value was in August, and the least was in May; the highest Fe2+value was in August, and the least was in July; the highest Fe3+value was in September, and the least was in July. On the spatial distribution, the highest TN value was at the outlet of Muling River (8#) where flow was fast, and the least was at Xipaozi (12#) which was surrounded by wetland species; the highest TP value was at Xinkailiu (1#) which had water exchange with Daxingkai Lake, and the least was at the outlet of Muling River (8#); the highest Fe2+value was at Liangzikou (6#) which was near the fish farm, and the least was at Xipaozi (12#); the highest Fe3+value was at the outlet of the irrigation flow (9#), and the least was at the outlet of Muling River (8#). The annual average N/P value in Xiaoxingkai Lake was10.98, which was lower than16:1, and the average N/P value of the sampling points was9.71, which was also significantly lower than16:1. Our research indicated that there existed of N limit all over the year in Xiaoxingkai Lake, and so the nitrogen-fixing Anabaena azotica was the main dominant species. The correlation of phytoplankton’s biomass and abundance with TN and TP was not significant, but it was significant with Fe2+and Fe3+.The content and existing forms of soluble iron (Fe3+and Fe2+) significantly affected the phytoplankton’s growth in Xiaoxingkai Lake.