Population Dynamics And Environment Factors Of Phytoplankton In Dianshan Lake

As the largest natural lake of drinking water sources in Shanghai, Dianshan Lake is an important protected area of ecological reserve and water source in the upper reaches of the Huangpu River. From January 2014 to December 2015, collecting samples of phytoplankton of the 12 sampling sites set in Dianshan Lake in the middle of month, a total of 24 samples, and mainly studing the composition of phytoplankton species, biomass, the dominant species etc. Meanwhile, evaluating the water nutritional status by using diversity index, environmental factors, deeply discussing population dynamics and the characteristics of the ecological niche of the dominant species for the sake of the key factors causing the spce-time dynamics. The main results are as follows:1、From January 2014 and December 2015, were identified Dianshanhu phytoplankton 151 taxa, belonging to 8 phylum 96 genera. Chlorophyta were found among 41 genera 81 species, accounting for 53.64% of the total; Bacillariophyta were found 21 genera 25 species accounted for 16.56% of the total; Cyanophyta were found 15 genera and 21 species, accounting for 13.91% of the total; Euglenophyta were found 5 genera 9 species, accounting for 5.96% of the total; rest of the identified species include: Chrysophyta were found 5 genera 6 species, Dinophyta were found 3 genera and 3 species, Cryptophyta were found 5 genera 5 species, Xanthophyta were found 1 genera 1 specie.2、The average number of phytoplankton biomass is 1828 ten thousand / L in Dianshan Lake, including Cyanophyta of 58%, Bacillariophyta of 24%, Chlorophyta of 9%, Cryptophyta of 8%, the rest of 1%. The phytoplankton biomass changes significantly over time, in general, the highest number of biomass in summer, at least in winter. The horizontal distribution of phytoplankton shows that the number of biomass in the middle of lake higher than the number of biomass in lakeshore, shipping lane and Yuandang Lake.3、The seasonal succession of the dominant species of phytoplankton is as followed: Cyanophyta-Bacillariophyta type in summer, Cryptophyta type in summer, Cyanophyta-Bacillariophyta-Cryptophyta type in autumn, Bacillariophyta type in winter. The dominant species throughout the year are Chroomonas acuta, Skeletonema potamos. The main dominant species are Pseudanabaena sp., Skeletonema potamos and Cyclotella sp. in spring. The main dominant species are Merismopedia minima and Microcystis sp. in summer. The main dominant species are Merismopedia minima, Skeletonema potamos and Chroomonas acuta in autumn. The main dominant species are Cyclotella sp. in winter.4、The Trophic State Index of Dianshan Lake is 68.37, indicating that the water is moderate eutrophication which decreases from northest to the southwest. The Shannon-wiener index indicates that the water is polluted slightly.And Shannon-wiener the index increase from northest to the southwest.5、The main factors affecting the distribution of Merismopedia minima are temperature and total phosphorus. The main factor affecting the distribution of Microcystis sp. is temperature. The main factors affecting the distribution of Pseudanabaena sp. are chemical oxygen demand and temperature. The main factor affecting the distribution of Skeletonema potamos is temperature and Chemical Oxygen Demand. The main factors affecting the distribution of Cyclotella sp. and Melosira sp. are temperature and total nitrogen. The main factors affecting the distribution of Chlamydomonas globosa are chemical oxygen demand and transparency. The main factors affecting the distribution of Chlorococcales are chemical oxygen demand and temperature. The main factor affecting the distribution of Chroomonas acuta is interspecific competition. In general, From the time perspective, the main factor affecting the distribution of phytoplankton is temperature, and subordinate factors are nutrients and interspecific competition. From the space perspective, the main factors affecting the distribution of phytoplankton are nutrients.6、The niche breadths of Chroomonas acuta, Chlamydomonas globosa, Cryptomonas erosa, Cyclotella sp. and Melosira sp. are wide because of the values of niche breadths all higher than 0.5 in each season of the year. The niche breadths of Synura spinos, Aphanocapsa delicatissima, Microcystis sp., Chroococcus limneticus are narrow. Skeletonema potamos, Microcystis sp., Chroococcus limneticus belong to the algaes of aggression, and the aggression of Skeletonema potamos is the strongest. Meanwhile, the rest is the algaes of recession, and the recession of Melosira sp. is the strongest.