| The eutrophication of Zhushan Lake, which is in the north of Tai Lake, has a tremendous impact on the development of the cities around it, especially the utilization of water resources. Based on its importance, the article chooses blue-green algae cell density of Zhushan Lake as the main object of study, which characterize the eutrophication. The article systematically investigates the spatially and temporally dynamical distribution of N, P and other water quality factors in Zhushan Lake and analyze the relationship between the cell density and water quality factors including TN, TP, WT. Based on the SPSS’s stepwise regression analysis, the main impact factors to algal biomass are filtrated and quantitative relationships between them are established. Finally, the prediction models for the main impact factors are built and the algal density of the year 2016 is predicted. The analysis and model can provide the some basic theoretical supports for the governance of water basin.Main observations and conclusions are summed up as following:(1)The water quality of Zhushan Lake, which is moderately eutrophic, is not as good as V category during the period of study and the factor affecting the water quality is mainly TN. The proportion, days of a month when the water quality is not as good as V category in a whole year is gradually decreasing, which means the water quality tends to improve. From the temporal and spatial analysis, the water quality is worst in Baidu port. The eutrophication factor of the lake inlet has a higher concentration compared with that of other locations of the lake. However, the algal density is the opposite case. High concentrations of TN, NH3-N happen in March, namely the end of the winter. What’s more, the trends of TP and permanganate index have no obvious dependences on time. And the reasons for changes in concentration of TP and TN are inconsistent. TP and permanganate index have little dependence on the algae’s growth and death.When the overlying water’s temperature of Zhushan Lake is about 24℃, the growth rate of algal density is significantly accelerated.(2)Correlation analysis results indicate that the order of correlation between water quality factor and algal density is the following:algal density-temperature>algal density-permanganate index>algal density-TN>algal density-NH3-N>algal density-pH> algal density-TP> algal density -dissolved oxygen. The reason of poor correlation between algal density and TP is that there exists many inflowing rivers which have a significant impact on water.(3)Through the stepwise regression analysis, the screened-out factors which are closely related to algae density are water temperature, pH, and total nitrogen. Then a quantitative relationship is established, namely, lny=-4.635+1.3191nWT+3.9311npH-0.643InTN. The analysis demonstrates that the regression data have a poor predictability in the peak of algae, but the deviation is in an acceptable range, so the regression model has a certain practical significance.(4)ARMA (2,2) model is established for TN, ARMA ((1,2,4),6) model for WT. The deviation between model fitting values and the measured values is within ± 15%, suggesting the effectiveness of the models. The article also predicts the main impact factors and algae density of the year 2016. The density of algae is predicted that there is a certain degree of difference between predicted values and actual values in summer, but the forecasting basically meets the general requirements of practical application. On the basis of the analysis and prediction, suggestions are put forward according to the characteristics of the ZhuShan lake’s water quality.
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