| Lake Taihu, located at the southern edge of the Yangtze River delta, is one of the largest freshwater lakes in China. The Taihu Basin is one of the most economically prosperous region of China. With a large number of people living there, serious water eutrophication often happens in this area. Because of eutrophication, water ecology problems such as the frequent occurrence of cyanobacteria blooms, the emergence of aquatic ecosystem degradation and other issues. From the 1990 s, black spots started to appear in the west of Lake Taihu and Meiliang Bay and other areas. And the frequent outbreaks of cyanobacterial blooms brought harmful eutrophication which influenced largely on the life of local people. After the over pile-up, the blue-green algae was corrupted by certain meteorological and hydrological conditions, smelly odor was released and black spotss occur. The occurrence and development of black spots are often rapid, but these can cause a great impact on the aquatic ecosystems, fishery industry and lives of nearby residents. However, the research of black spots is still insufficient in the present stage.A series of related field experiments and lab analysis have been carried out, in order to study the development of black spots and eliminating the potential risk of algae-caused black spotss in Lake Taihu. Through the study, we got the following results:1.A series of samplings have been collected during the day of June 22, 2013 to 27 in Meiliang Bay for the occurrence of algae-caused black spots. Water quality and phytoplankton and dissolved taste and odor compounds(T&O) were monitored. Through experiments, we found that a large amount of TN and TP and NH4+-N and dissolved T&O were released into water after black spots happened. The analyses of dissolved T&O and environmental factors showed that, there are significant positive correlations between dissolved T&O of thioethers and conductivity、total dissolved solids、TN、TP and NH4+-N and a significant negative correlation between the dissolved T&O of thioethers and dissolved oxygen. But we did not find the relationship between cyanobacterial biomass and odor substances, which is probably because the large number of cyanobacteria had been corrupted when the black spots was found. In situ simulation by enclosures of algae-caused black spots should been manipulated to obtain more data.2.A 40-day study of in-situ simulation by enclosures had been implemented from June to September 2014 in Meiliang Bay of Taihu Lake,to study the process and capture the environmental influences of algae-caused black spots. The enclosures of experimental groups were added cyanobacteria, and the concentration of the added wet weight of algae was about 10000 mg/L. By enclosure-experimental method, we successfully obtained black and odorous water which was highly similar with the water caused by natural algae-caused black spots. In this study, we have found that the long time over accumulated cyanobacteria can lead black spots with high temperatures in summer. During black spots events,the concentration of dissolved oxygen and p H reduced to 0 mg/L and 6.67, respectively, while TN and TP increased to 40 mg/L and 10 mg/L, respectively. By black spots,a great deal of N and P and other nutrients were released into the water,rapid up taking and depuration of nutrients into water was caused,and the water cycle rate of nutrients was promoted. The black and odorous water was acidic and seriously lack of oxygen, which showed a trend of deterioration of algae corruption. The occurrence of black spotss affected the growth and reproduction of aquatic organisms, and severely damaged the biodiversity of water ecosystem.In order to prevent algae-caused black spotss, the input of nutrients in Lake Taihu must be controlled, and measures of meteorology monitoring, remote sensing, field patrol and other means must be taken to control the growth of algae. Salvage operations should be carried out as early as possible in the area of cyanobacteria gathering, aeration equipment is better to be prepared. |
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