Research On Factors, Control And Management System Of Cyanobacteria Blooming In Water Source In Shanghai

With a rapid increase rate of economic development and population expansion, the sum of pollutants in the water increased every year, especially in the downstream region of Yangtze River, which suffered a rapid urbanization process recently, the eutrophication occurred in every shallow lakes in that region. These lakes were the main drinking water source for the local residents, and due to the increase of the frequency and scale of Cyanobacteria blooming, the water supply was in danger, the water plant nearby was off-set. Shanghai is located in both the lower regions of Taihu Lake basin and the Yangtze River estuary region, and the first time of Cyanobacteria blooming occurred in Shanghai was 1985 in Lake Dianshan. Recently, Cyanobacteria blooming also appeared in the new reservoir in Yangtze River estuary region, so it became a urgent problem for the safety of the drinking water source in Shanghai. This thesis chose the water sources as the objects in upper stream region of Huangpu River and in Yangtze River estuary region, and used the theory and measurement of the environmental science, environmental engineer, ecology and management to analysis the Cyanobacteria blooming in Shanghai in many aspects, based on the results of the simulation experiments and the ecological survey. For the lakes, the research focused on the cause and evaluation of Cyanobacteria blooming, and set up a management system including the ecology restoration and response system fo rthe blooming. For the reservoir, the research method changed to ecological survey and stimulation, and the forces of management changed to early warning and control for the blooming. All the results showed below:The core of the water source in Shanghai had changed due to the deterioration of water quality. In 2010s, there were three main changes:the sum of water supply was gradually expanding to 1.72×107 m3/d from the level of 9.51×106 m3/d in the end of last century, and the new core of water source was Yangtze River estuary region, and the mode of water supply changed from the open resource to the reservoir. The analysis results showed that the main problem of water quality in different water source was the increasing concentration of nitrogen and phosphorus. The quality in minor rivers was more inferior to that of Lake Dianshan and Huangpu River, but the quality in Yangtze River estuary region was superior. In that case, the water quality of Shanghai would be improved by the water from Yangtze River estuary region, but it didn't mean all the problems were solved. Occasional cyanobacteria blooming in Chenhang Reservoir in summer showed that the prevention and control of alga would last for a long time.Cyanobacteria blooming in Lake Dianshan were a complex consequence of nutrient increase, ecological degradation and environmental factors. The net input of nutrient was increase to 3026.5 tN/a in 2009 from the number of 220.2 in 1985, and the numbers in 2009 and 1985 for phosphorus were 39.3 and 6.0 tP/a. The causes included the net amount of the nutrient increase mainly from the increasing concentration of upper stream, which had overload. Another was the ecological degradation caused by Macrophytes disappear, and the biomass of fish and Benthos decreased. Phytoplankton became the key factor of the lake succession, and the biomass of cyanobacteria blooming became the largest.Increased nutrient loading was one reason of blooming, and another were the environmental factors, which effected the unfixed blooming time and region. The variations of blooming time, region (based on the results of MODIS analysis), hydrology and weather revealed some rulers about blooming in Shanghai during the cyanobacteria blooming in 2007-2009:the high temperature in Shanghai induced a large biomass in short time; the backwater effect to Lake Dianshan from Huangpu River and Taipu River extended the hydraulic retention period, and benefited the cyanobacteria proliferation; cyanobacteria floated up to the surface controlled by a special buoyancy regulation mechanism, and gathered in a low pressure, so the blooming formed eventually.Cyanobacteria blooming were a natural feedback mechanism to the nutrient overload in water. The blooming occurred in every shallow lake located in the downstream of the Yangtze River region. In this way, nutrients in water were reduced, but the cyanobacteria were not easy to collect due to a large area, so it became a main problem for drinking water supply. a fundamental measure for controlling outbreaks was to rebuilt the eco-system in Lake Dianshan by increasing biodiversity and extending the recycle processes of nutrient.The blooming possibilities in Qingcaosha Reservoir were quite low, but it didn't include the stagnant water areas in the reservoir. The water quality in Yangtze River estuary was good, and the impact from land emission was low, but the increasing nutrient concentrations had been close to the respective limit values. The concentration of nutrient in Qingcaosha Reservoir was lower than the origin, and the ratios of inorganic forms was low, which means the consumption of nutrient were mainly from the increasing biomass of phytoplankton, especially for the cyanobacteria, and the less part were Deposition into the sediments.The distribution areas of macrophysics were large, but the construction was simple, and the biomass would decline if the human activities enhanced. The total amount and types of phytoplankton were lower than that of Lake Dianshan, but increased with the higher temperature, and the peak value appeared in August. The community construction of phytoplankton had been completely changed as the freshwater reservoir types. The main types of Cyanobacteria were Oscillatoria and Anabaena, increasing with higher temperature. The biomass of Cyanobacteria increased to the largest in some spots in August. Cyanobacteria are mainly distributed in the swallow water like the influent area and both side of Qingcaosha. The specific heat capacity of the reservoir was so high that the temperature in October was still benefit for the reproduction, and it may be an adverse factor in the reservoir.The double proliferate time of cyanobacteria was extended to about 20 days, even lower than chlorophyta, due to low nutrient concentrations in the reservoir, and it fundamentally limits the possibility of cyanobacteria blooming in the short period of time. The best temperature for cyanobacteria was 24, so the result of ecological survey showed that the biomass increase of cyanobacteria started from May, and the illumination did no effect on it. However, the changes in hydrology conditions could limit the growth of cyanobacteria, especially in a rapid flow.10 days was the longest time for cyanobacteria in a rapid flow without nutrient supply, and the cells became decomposition, or even death. So for the semi-nature reservoir, hydro scheduling may be the best management for the blooming control.Due to the reasons above, the possibility of cyanobacteria blooming in Qingcaosha Reservoir was low in a longest hydraulic retention period of 21 days, but considering the nutrients from the sediment, the blooming may appeared in some parts of the reservoir when the hydrological conditions changed.To control the cyanobacteria blooming in urban water source in Shanghai, the management should consider the types of water sources, nutrient status, hydrological characteristics and history of the blooming, and establish different management system for different water source aimed at the blooming control. The management system for Lake Dianshan includes two parts:emergency response and algal control measurement. The time-based feature evaluation index system was employed to evaluate the blooming in Lake Dianshan, and some control measures to protect drinking water sources. But these emergency measures couldn't solve a fundamental core issue of excessive nutrient concentrations in the lake, so a long-term control measures including Lake Ecosystem Restoration need to adopt in the management system.Both the ecosystem and water quality in Qingcaosha Reservoir were in a good condition. Although the probability of the cyanobacteria bloomin was low, it still may appear in under the benefit hydrological or weather conditions in such a semi-nature water source. The management should include both the early warning, prevention and control strategy, in order to establish a stable ecosystem in the reservoir, cut off the source load, increase the diversity, et al., aimed to reduce the probability of the cyanobacteria blooming...