Study On Phytoplankton Standing Stock And Trophic Level In Lake Dianshan

Chlorophyll-a is one of the necessary pigments for phytoplankton to do the photosynthesis, is a common chlorophyll type of all the phytoplankton categories. Its concentration is an important indicator of the phytoplankton biomass. And it’s also important in reflecting the eutrophic waters’quality. Lake Dianshan is one of the drinking water conservation areas in Shanghai with other important functions in ecology, fishery, water transportation, etc. In1985,It started algae bloom for the very first time. Since then, the water environment has got worse and worse, and the aquatic ecosystem security has been severely threatened. In order to know the changes in phytoplankton standing stock and their relationships with the environment factors, also to identify the trophic level in Lake Dianshan, an investigation was carried out from December2010to November2011. In this period,10sampling sites(both in the depth of0.5m and1.5m) were selected and the samples were investigated once a month. The Chi.a, phytoplankton density, water temperature, pH, DO, SD, TN, TP and TN/TP were the factors that have been investigated. The main results are as follow:1) During the survey period, the Chl.a was from0.17to144.68mg/m3and the average number was20.05mg/m3. Phytoplankton density was from0.82to72.27×106ind/L and the average number was12.48×X106ind/L. Water temperature was from1.2to33.3℃and the average number was17.9℃. The pH was from7.4to9.0and the average number was8.1. The DO was from3.00to27.70mg/L and the average number was9.07mg/L. The SD was from40to150cm and the average number was72cm. The TN was from0.42to9.34mg/L and the average number was3.19mg/L. The TP was from0.04to0.56mg/L and the average number was0.18mg/L. The TN/TP was from3.19to216.21and the average number was19.96. During the period, all the factors in two different depth showed a highly significant positive correlation (P<0.01) and their differences were not significant. However, in different months, the correlations and the differences were slightly different. Overall, the sampling sequence slightly affected the water temperature, and the water temperature in1.5m depth was a little lower than that in0.5m depth. The overall pH was slightly alkaline and it was lower in summer. In all the DO values, there were65.83%who met the surface water type I standard and the DO values in the S4who was at the northern part of the Lake were lower than the average. The SD value was a little higher than the previous measured values, and it was lower in the northern and central part. Meanwhile, the SD value had2peaks in the period. In all the TN values, there were67.08%inferior to the surface water type V standard and the TN values were higher in northern part and in spring. In all the TP values, there were65.83%met the the surface water type III standard and the TP values were higher in northern part and in winter. Also, the TN/TP was higher in the northern part of the Lake.2) All the data collected in the investigation could be divided into4parts. In the temporal scale, March to may belonged to the spring. June to September belonged to the summer. October to November belonged to the autumn. And December to February belonged to the winter. In the spatial scale, S4belonged to the A region. S2belonged to the B region. S3belonged to the C region.Sl,S5,S6, S7, S8, S9and S10belonged to D region.3) The impacts of each factors on the Chl.a were different in different scale. In the temporal scale, TP, phytoplankton density and SD were the main impact factors to the Chl.a. Other factors’influences were in the order of TN, DO, Ph, water temperature and TN/TP. In the spatial scale of0.5m water depth, the influences of all the factors were in the order of phytoplankton density, DO, pH, SD. Water temperature, TN, TP and TN/TP were not significant correlated to the Chl.a. In the spatial scale of1.5m water depth, the correlation between Chi.a and environment factors were weaker than that in the depth of0.5m. Phytoplankton density and Chi.a was in a good correlation followed by pH and SD. The water temperatures, DO, TN, TP and TN/TP were not significantly correlated to the Chi.a. Overall, the correlations between Chl.a and other factors were best in A region and worst in C region. And they were better in spring and summer than that in autumn and winter.4) The impacts of each factors on the phytoplankton density were different in different scale. In the temporal scale, Chl.a, SD and water temperature’s correlations with phytoplankton density were better than pH, TP and DO’s. TN/TP and TN’s were even worse. In the spatial scale of0.5m water depth, the influences of all the factors were in the order of Chl.a, DO, pH and SD. Water temperature, TN, TP and TN/TP were not significant correlated to the phytoplankton density. In the spatial scale of1.5m water depth, the correlation between phytoplankton density and environment factors were weaker than that in the depth of0.5m. Their correlations were in the order of Chl.a, pH and SD. Water temperature, DO, TN, TP and TN/TP were not significant correlated to the phytoplankton density. Overall, the correlations between phytoplankton density and other factors were better in summer and winter than that in spring and autumn. And the correlations were best in A region and worst in C region.5) The impacts of each categories’phytoplankton density on the Chl.a were different in different scale. In the temporal scale, each categories’phytoplankton density had a significant correlation with Chl.a. Bacillariophyta, Chlorophyta and the Cryptophyta’s phytoplankton density had best correlations with Chl.a. Followed by Cyanophyta, Chrysophyta and Euglenophyta, and then followed by dinoflagellates and zooxanthellae. And the correlations were in the order of summer, autumn, spring and winter. In the spatial scale of0.5m water depth, the correlations were better in Dinoflagellate and Chlorophyta. Followed by Bacillariophyta, Cyanophyta and Cryptophyta. And then followed by the Zooxanthellae and Euglenophyta. Chrysophyta phytoplankton density was not significantly correlated with Chl.a in the entire lake. In the spatial scale of1.5m water depth, the correlations were better in Chlorophyta. Followed by Bacillariophyta, Dinoflagellates, Cyanophyta and Cryptophyta. And then followed by Euglenophyta. Xanthophyta and Chrysophyta phytoplankton density were not significantly correlated with Chl.a in the entire lake. The correlation in A region was the best, followed by the D region. Correlations in B region were a little better than that in C region.6) Using TLI(E)s as the indicator, Lake Dianshan was in light eutropher. A region, which was in the northern part, was in middle eutropher, followed by D region, C region and B region. The B,C and D region were all in light eutropher. The nutrient level was higher in spring and summer, and it was lower in autumn and winter. All the factors’trophic state indexes were higher in A region. And the comprehensive nutrional statue indexes varied in different regions. Using Chl.a as the indicator, Lake Dianshan was in eutrophic, which was slightly different with the result indicated by TLI(E)s.