Study On The Structure Of Phytoplankton Community And Its Relationships With The Environmental Factors In Dishui Lake

Dishui Lake is a large newly-bulit lake on beach, so far it is the largest man-made landscape lake in our country. This research on Dishui Lake and its around waters has 9 sample sites (8 sites in Dishui Lake), sample every month from January to October in 2007. The delicate research of the community structure and distribution of phytoplankton is based on the monitor of physichemical index , analyze the diversity of phytoplankton using diversity index, analyze and discuss the relationship of phytoplankton and physichemical index in the meanwhile using these factors to value water quality. All these work can provide most basic data for the protection of environment and the material for the research on river or reservoir. Here are the results:1. The yearly average temperature of Dishui Lake is 18.25 degrees, the variable span is from 6.1 degrees to 28.8 degrees; there is no difference on transprancy between differents sites, the average is 50.6 centimetres, but the around waters, is higher than the lake, It is 56.5 centimetres; the average PH is 9.00, which showed the quality took on alkaline; the average salinity affected by the beach is 2.81g/1000g, higher than the other lakes; there is no big change on averages of OD(9.98mg/L), COD(12.38mg/L), TN(1.12mg/L), TP(0.10mg/L), according to the ratio of TN/TP, Dishui Lake is P-limited lake.2. There are 86 species of phytoplankton, which belonged to 55 genera of 8 phyla.Most of them are freshwater species; dominant species ascribing to Chlorophyta accounted for 50 percents and the quantity is 43 species belonging to 23 Genera; secondly the percentage of Cyanophyta is 30.4. Chromulina, Chlamydomonas, Ankistrodesmus, Oscillatoria, Cocconeis are dominant species in Dishui Lake, but the dominant species of its around waters are Chromulina, Chlamydomonas, Raphidiopsis, Chaetoceros, Cylotella and Cryptomomas. The same change occurred between species and generas on the seasonal change, the minority in January and the majority in May; the Chla which accounted for the most propotion can influence the entire change trendency of phytoplankton.Phytoplankton community structure takes on a trait of little-shape and large number . The largest number of the spceies appeared in May. The seasonal change of phytoplankton biomass could be influenced mostly by Chromulina in Dishui Lake. The yearly average concentration of Chla is 29.35mg/m3, and its horizontal and seasonal distribution just coincidenced with biomass of phytoplankton.3.The correlation analysis on the physichemical index and biological index of Dishui Lake: There is strong correlation between the quantity and salinity,DO,SD. And the strong correlation also lies in the relationship of salinity and quantity of phytoplankton,Chromulina,DO,SD. So we can conclude that sanlinity is the bridge of phytoplankton and physichemical index.4.Evaluation about eutrophication of Dishui Lake using physichemical index,phytoplankton index and corrected Carlson Trophic State indexes.All results showed different, some factors included physichemical index, Chromulina and the dominant species showed that the lake was in a status of semi-eutrophication, but using the biomass and TSI showed the result was eutrophication. All this showed that to value the status of eutrophication has some restrictions using signal index. So that the water quality of Dishui Lake lies in the status of semi-eutrophication.