| Nansi Lake, is the largest freshwater lake in northern china, and it is also a significant regulating lake and water channel in the east route of South-to-North Water Diversion Project. Therefore, the water quality of it plays a important role in the the safety of water supply in this project, at the same time, it may also influence the development of both industry and agriculture and the living quality of urban residents in the surrounding areas of Nansi Lake. As Phytoplankton is sensitive to the changes of water environment, the study of phytoplankton community distribution characteristic and succession rules can reflect water environment quality more comprehensively and objectively. Our research group is conducting a long-term systematic study focusing on phytoplankton community in Nansi Lake. In this project, the spatial and temporal variation characteristics of phytoplankton community in a long-term sequence (from May 2010 to May 2015) had been determined and meanwhile the environmental factors influencing the spatial and temporal variation of phytoplankton community had been analyzed. This study will provide theoretical basis and technical guidance for aquatic environment protection in Nansi Lake. Moreever, it may provide phytoplankton data and research basis for the evaluation of aquatic environmental alterations in the future.The differences of water quality parameters between each season and each sample were worked out by one-way analysis of variance. The similarity of species composition of phytoplankton between seasons and samples were compared by Jaccard index. The similarity of phytoplankton community of each season and sample were figured out by non-metric multidimensional scaling. The driving environmental factors influencing the temporal and spational variations of phytoplankton community were determined by redundancy analysis.307 phytoplankton species which belong to 121 genera in 8 phyla (including Chlorophyta, Bacillariophyta, Cyanophyta, Euglenophyta, Xanthophyta, Cryptophyta, Pyrrophyta and Chrysophyta) had been identified in Nansi Lake from May 2010 to May 2015,.The seasonal change of phytoplankton in Nansi Lake in species composition, cell density, dominant species and community structure were obvious.229 phytoplankton species which belong to 102 genera in 8 phyla had been identified in spring.259 phytoplankton species which belong to 113 genera in 8 phyla had been identified in summer.241 phytoplankton species which belong to 101 genera in 8 phyla had been identified in autumn and 210 phytoplankton species which belong to 94 genera in 8 phyla had been identified in winter. The species similarity index beteween seasons ranged from 0.65 to 0.74 (a medium similarity level) according to Jaccard index analysis, which showed that species composition of phytoplankton changed seasonally. The mean of phytoplankton cell density in winter was significantly lower than the other seasons, it had an apparent increasing trend from spring to autumn with the maximum in autumn, and then sharply dropped down in winter. Some of the dominant phytoplankton species in different seasons were same and some were different. Chlorella vulgaris and Chroomonas acuta had been identified and the dominances of them were the top two during all four seasons. Cyclotella meneghiniana was the dominant species in spring, summer and winter. Pseudanabaena limnetica was the dominant species in summer and autumn. Chromulina elegans was the dominant species mainly in spring and winter. The Non-metric Multi-dimensional Scaling analysis showed that the phytoplankton community structures in Nansi Lake had obvious seasonal differences and the temporal dynamics of phytoplankton was as follows:Chlorophyta-Bacillariophyta-Cryptophyta (spring), Chlorophyta-Cyanophyta-Bacillariophyta (summer), Cyanophyta-Cryptophyta-Chlorophyta (autumn), Chlorophyta-Bacillariophyta-Cryptophyta (winter).There were some changes of spatialdistribution of phytoplankton in Nansi Lake about species composition, cell density, dominant species and community structure. 262 phytoplankton species which belong to 110 genera in 8 phyla had been identified at sampling site S1.242 phytoplankton species which belong to 106 genera in 8 phyla had been identified at sampling site S2.231 phytoplankton species which belong to 104 genera in 8 phyla had been identified at sampling site S3.235 phytoplankton species which belong to 106 genera in 8 phyla had been identified at sampling site S4. 239 phytoplankton species which belong to 103 genera in 8 phyla had been identified at sampling site S5. The similarity index between sampling sites changed from 0.73 to 0.79 (a medium to highly similarity level) according to Jaccard index analysis. The variation tendency of phytoplankton cell density at all sampling sites were roughly consistent and the cell density was higher in summer and autumn than that in spring and winter. However, phytoplankton cell density was different in each sampling site. The mean of phytoplankton cell density at sampling site S1 was significantly higher than the other sampling sites and that of sampling site S4 was the lowest. The dominances of Chlorella vulgaris and Chroomonas acuta were the top two at all sampling sites Pseudanabaena limnetica was the dominant species at all sampling sites except for S4. Cyclotella meneghiniana was the dominant species at sampling sites S1, S2 and S5. Microspora stagnorum and Cyclotella stelligera was the dominant species at sampling site S2 while Monallantus brevicylindrus was the dominant species at sampling site S4. The Non-metric Multi-dimensional Scaling analysis showed there were some differences in spational phytoplankton community structures in Nansi Lake but not remarkable.The major environmental factors influencing phytoplankton distribution of Nansi Lake in spring were total nitrogen, total phosphorus and ammonia nitrogen. The major environmental factors influencing phytoplankton distribution in summer were temperature and total phosphorus. The major environmental factors influencing phytoplankton distribution in autumn were total nitrogen, total phosphorus and pH with them in winter were total nitrogen and pH. The major environmental factors influencing phytoplankton community structures in sample S1, S3, S4 were temperature, total nitrogen, total phosphorusand pH with them in sample S2 were temperature, total phosphorus and permanganate index and sample S5 were temperature and total phosphorus. Based on the analysis of redundancy analysis and one-way analysis of variance for water quality parameters, the main driving environmental factors affecting seasonal changes of phytoplankton community in Nansi Lake were temperatureã€.nitrogen and total phosphorus while the main driving environmental factors affecting spational changes of phytoplankton community in Nansi Lake were permanganate index and total phosphorus. |
