Multiple Inducements Analysis And Trend Prediction Ofalgal Blooms In Western Lake Chaohu

In recent years, harmful algal blooms (HABs) frequently occurred in the lakes and ponds of China with expanding covered area and increasing intensity. The Lake Chaohu is one of the five most important fresh lakes in China, and is also the largest one in Anhui Province. According to the monitoring data from local administration departments, 70% lake surface was eutrophic water. Especially in the western Lake Chaohu which closes to the Hefei City, the lake water degraded to serious eutrophication for a long period. In this century, there were more than 10 times disasters concerned with blue-green algal blooms, which brought much hazards to feedwater security in the city and countryside. The study on multiple inducements and trend prediction of algal blooms is helpful for establishing the theory and technical system which can indentify the HABs inducements and simulate the dynamic movement of algal biomass, and upgrade the coping capacity to HABs.Therefore, focused on the multifactor coupling effects of environmental factors categorized in water quality, meteorology and hydrology on HABs, the thesis determined correlations between algal biomass and environmental factors to identify the HABs inducements, explained the relationship between algal blooms and multifactor coupling in natural environment, created the efficient prediction models of HABs, analyzed the dynamic movement trend of algal concentrations, and provided the control methods of HABs by the approaches of correlation analysis, principle factor analysis and multivariate time series analysis.The main research conclusions are listed below.Through the principle factor analysis, environmental factors correlated to HABs were used to establish factor models which dominate algal blooms potentially. In the model, the complex relationship among environmental factors was explained by few common factors. The results indicate that HABs inducements in Lake Chaohu are air temperature, nutrients loadings, light intensity and water level. In summer, HABs mainly influenced by the common factor concerned with air temperature; and mass-algal reproduction in spring is mostly affected by common factors related to nutrients loadings, meteorologic and hydrologic conditions, such as wind speed, light intensity and water level.The multivariate time series models (ARIMAX) with input variations concerned with environmental factors were accomplished to simulate and forecast the dynamic variation of chla concentration. With satisfied simulating accuracy, the ARIMAX models were applied to quantitatively predict the variation of chla concentration in coming period using historical monitoring data. And the model was shown in well applicability of trend forecast to various regions. Results from the analysis to trends of algal dynamic movement indicates that HABs caused by the combined effect of multiple environmental factors. In the spring, the water body is required to retain higher nutrient loading(CODMn,BOD,TP) and certain pH,water level for the reproduction of algae. During the transition of spring and summer, the nitrogen loading in water should keep rising with the extending of sunlight. Depending on above environmental conditions, the high temperatures in summer will induce the HABs in the lake.Correlations between the environment factors (water quality, meteorologic and hydrologic factors) and chla concentrations were quantized to select the marked inducements of HABs and analyze the multifactor coupling effects to inducements identification. The modified method of partial correlation analysis in categories was developed to efficiently identify the HABs inducements from environmental factors under their multiple coupling effects.Used environmental factors as independent variable and chla concentration as dependent variable, stepwise multivariate regression models were accomplished to simulate the chla concentration's movement. With the advantage of well operability, the multiple regression model is applicable to the qualitative forecast of the HABs trend. Besides, the model selected water level, TN, CODMn and air temperature as reserved variables, agreed with correlation analysis and principle factor analysis.Distribution characteristics of HABs in Western Lake Chaohu were also analyzed in the thesis. The dominant bloomed algal population in summer consisted of Microcystis aerugeosa and Anabaenaflos-aguae, appeared seasonal movement as summer increase and winter decrease, and this summer peak values steady declined by years while winter values kept stable. Occurred frequently from July to September, HABs mainly gathered in the river mouth of Tangxi and Paihe, and then floated to middle area of western lake followed the route from northern to southern of lakeside.The results of this thesis provides scientific foundations to prediction and control researches of HABs in Chaohu Lake, and also supports the investigations of HABs in other regions as theory and reference.