| Huizhou reach of Dongjiang river located in middle reaches, the water quality was very important for water supply. Over the yeas, by the adverse effects of pollution in Xizhi River and Danshui River and because of human factors influence such as cascade development and rapid regional economic development, aquatic ecosystems in Huizhou reach of Dongjiang river damaged, the level of eutrophication was seriously, brought much danger in water supply. Therefore, the investigation on the eutrophication situation of this reach is very important. TO protect the quality of Dongjiang river, surveys on the phytoplankton and aquatic environment factors were carried out every months from January2011, the results of this study were as follows:(1) The main pollutants in Huizhou reach of Dongjiang river were nitrogen (TN, NH3-N), phosphorus (TP) and organic substance(BOD5, DO).(2) Total129,120and103species of phytoplankton were identified in main stream, Xizhi river and Danshui river respectively, which was mainly composed of the Chlorophyta and Bacillariophyta. Average densities of Alga were ranged from2.23×105cells/L to8.04×106cells/L in main stream, and1.60x105cells/L-1.17×107cells/L in Xizhi river,7.04×105cells/L-1.36×107cells/L in Danshui river. Cryptomonas ovata Ehr. was the dominant species in main stream through the year, and was the dominant species in Xizhi river expect July. Although the water quality of main stream was in a light or no pollution state, the spatial difference was evident, pollution in Jiantan reservoir especially waters where Xizhijiang drains into was much more seriously, water quality of Danshui river and Xizhi river was much more seriously than main stream.(3) CCA showed that, the important environmental factors which affected the distribution of phytoplankton of main stream were pH, BOD5, TP, DO, orthophosphate, NH3-N, CODMn, TN, conductivity and NO2-N, while CODMn, turbidity, SD, DO, silicate and ammonia nitrogen in Xizhi river.(4) Temporal and spatial differences in eutrophication is obviously in main stream, Jiantan reservoir where Xizhi river drains into (the D4, D5and D6) was the sensitive waters, early wet season (march and April) and summer (August) were the sensitive periods. X1and X3were the most serious sample sites of Xizhi river, April and October were sensitive periods. The water quality of Danshui river is in mesotrophic, January, March, may and July were sensitive periods in this reach.(5) By using principal component analysis and stepwise regression analysis, we got the following modeles:algae density prediction model of D4:1g (algea density)=0.068F2+6.422, Chl.a prediction model:Chl.a=3.599F2+21.111, F2=0.926TN+0.917PO43-+0.885NH3-N+0.772cond+0.465TP+0.424SS-0.420NTU, the algae density prediction model of D5:1g (algae density)=0.053F1+6.276, Chl.a prediction model:Chla=4.582F1+20.124, density of dominant species prediction model:lg (algal density)=0.082F1+5.681, F1=0.966NH3-N+0.955TN+0.941cond+0.900BOD5+0.894SS+0.730DO+0.709NO3-N+0.696pH+0.643CODCr-0.492NTU+0.473PO43-. All kinds of forecasting model can be used in ecological risk prediction of Dongjiang river, and the models for Chl.a forecasting is the best.(6) Due to the potential ecologic risk of main stream, we should take effective measures as muchas possible, for example, increasing reduction efforts and the construction of deep purification facilities, strengthening the control of tributaries pollution, ecologicalrestoration and water ecological environment monitoring and so on. |
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