Effect Of Water Turbulence On The Algal Growth Mechanism And Eutrophication Control In QCS Reservoir

The Qingcaosha reservoir (QCS reservoir) is located along the Yangtze Estuary in thenorthern part of Changxing Island in Shanghai, China. QCS reservoir is a new water sourcein Shanghai, and is rich in freshwater resources from the Yangtze River. The water supplycapacity covers50%of the total water supply in Shanghai. More than10million peoplebenefit from it. The water quality of QCS reservoir is directly related to people’s lives andhealth. As an important water source, QCS reservoir plays a crucial role in affectingShanghai citizen’s health. Like other lakes and reservoirs, the QCS reservoir is also facingthe challenge of environmental deterioration: eutrophication and algae bloom. If algaebloom is excessive in the reservoir, a lot of harmful matters such as algae toxins enter thewater body. The water will pose a serious threat to the industrial water and domestic waterin Shanghai. The QCS reservoir is located in the Yangtze River estuary, which is thesubtropical monsoon climate zone. The water forms different turbulence intensities under“wind generating wave”. Water turbulence may directly affect the algal growth. On theother hand, the water flow may also form water turbulence, which also directly affects thealgal growth.In order to further explore how water turbulence affects the algal growth andeutrophication in the QCS reservoir water, the following work was done as shown in thepaper:1) We studied the effect of water turbulence on the growth and photosynthesis ofblue-green algae in the laboratory. The experimental blue algae include Microcystisaeruginosa and Anabaena flos-aquae, the green algae include Selenastrum bibraianum,Chlorella pyrenoidosa and Scenedesmus obliqnus.2) The paper studied the effect of waterturbulence on competition and photosynthetic responses of Anabaena flos-aquae andSelenastrum bibraianum in the laboratory.3) We studied the effect mechanisms which water turbulence affects on growth and photosynthesis of the algae in the laboratory.4) Byanalyzing the mechanisms CO2-limited，light-limited and the temperature differenceaffecting the algal growth, we studied the effect of water circulation algae controltechnology (WCACT) in controlling algal growth and eutrophication in QCS reservoir.5)We analyzed the eutrophication status of the water in QCS reservoir, and analyzed theeffect factors of the algal growth in QCS reservoir water.By a series of laboratory and engineering experiments in QCS reservoir, the followingresults were obtained:1) Under two culture modes of low nitrogen&phosphorus concentrations media andhigh nitrogen&phosphorus concentration media, the difference in water turbulenceintensity affected growth and photosynthesis of the single-culture blue-green algae. Theresults showed that water turbulence may accelerate algal growth. The effect mechanism isthat water turbulence accelerates algal growth by affecting its photosynthesis (includingphotosynthetic efficiency and electron transport rate), it does not only affects thedistribution and transmission of nutrient in media or water. Water turbulence increasesexchange between CO2and O2in water surface, having adverse effect on controlling thealgal growth and breakouts in water.2) Under two culture modes of low nitrogen&phosphorus concentrations media andhigh nitrogen&phosphorus concentration media, the experiment studied the growth of theco-culture blue-green algae. The results showed that there is definite competitionmechanism between the blue algae and the green algae. Water turbulence affectscompetition by affecting blue-green algae photosynthesis, and may inhibit the blue algalgrowth to a certain extent. Because the blue algae is the main producer of algae toxins, thecompetition mechanism may decrease the content of algae toxins in water. Thecompetition mechanism has a positive significance and importance for water quality safetyin QCS reservoir.3) The WCACT formed the vertical water flow by vertical ascending and diffusedwater flow by horizontal diffusion in its controlling range. Then the water flow generateswater turbulence. On one hand, CO2-limited，light-limited and the temperature differenceinhibited the algal growth. On the other hand, water turbulence inhibited the blue algalgrowth by the competition mechanism of blue-green algae. The result was verified byengineering experiment in QCS reservoir. 4) In QCS reservoir, there are many factors that affect the algal growth. Interaction ofthese factors results in complex and comprehensive effects of water turbulence on theblue-green algal growth. On the whole, water turbulence accelerates the algal growth byincreasing algal photosynthesis and exchange between CO2and O2in water surface. On theother hand, water turbulence inhibits the blue algal growth by the photosynthesiscompetition mechanism of blue-green algae, and may decrease the content of algae toxinsin QCS reservoir water.