| Algal bloom is a serious ecological problem in the process of lake eutrophication.In China,the high-intensity algal blooms of the“Three Lakes”such as Lake Taihu,Lake Chaohu and Dianchi have become to the landmark ecological problems in lake pollution control.In Lake Taihu,a large number of algal blooms rot caused ecological disasters named“black patch of bloom”?black bloom?and triggered the drinking water crisis of Wuxi City in May 2007.It made the algal bloom control engineering such as diversion,dredging,salvage and black bloom inspection,monitoring and early warning measures etc.became the key content in algal bloom control projects of Lake Taihu.However,the algal float on water surface and accumulate with wind,made the great challenges to algal bloom control.Part of the algal bloom'sedimentation brought new risk to arise black blooms.Therefore,the spatial variation of algal bloom needs to be urgently identified,and to improving the“algal control project”efficiency and preventing secondary disasters of control projects.This research relies on the topic of water pollution control and treatment of the national major science and technology project"Meiliang Bay cyanobacteria bloom control and algae-derived organic matter disposal technology integration and engineering demonstration"?2017ZX07203-001?.Combined the tracking surface particle flow GPS particle drift with high-density and multi-layer algal bloom related indicators which being investigated in the file.The temporal and spatial distribution characteristics and variation of algal bloom and their related water quality indexes were analyzed under the wind field in large shallow lakes.The location at which the Liangxi river meets Meiliang Bay was selected to explore the influence and controlling factors of algal blooms on connected river.The cyanobacterial particulates and water quality parameters including were monitored daily during the summer bloom season.The spatial variation in water quality parameters along the river were also surveyed to help investigate the effects of cyanobacterial blooms on the water quality of connected rivers and propose the water transfer management strategy for optimizing river water quality.The water quality,sediment quality and algae situation of the typical cyanobacterial salvage point and algae water separation station in Taihu Lake were investigated and studied.The risk of the control project of cyanobacteria salvage and algae water separation station on the flooding of nearby water bodies was evaluated.1?The wind field is a very important physical factor to control the formation of algal bloom in large shallow lakes.The surface lake current of Meiliang Bay responds rapidly to the change of synchronous wind field,and the lake direction has a high matching degree with the wind direction.When the average wind speed is 1.9 m·s-1 and 2.3 m·s-1,the surface flow rates are 3.0 cm·s-1 and 5.0 cm·s-1,respectively,which was characterized by average particle drift velocity.Under the action of wind field,the spatial pattern and dynamic change of cyanobacterial blooms in shallow water lakes have a great influence.The nutrients of particulate matter and cyanobacterial blooms have higher consistency,while the dissolved nutrients are opposite.2?Cleaning algal blooms along the lake shoreside is limited in restrain algal bloom in large lakes.The cyanobacterial biomass stock in the surface water was estimated according to survey of the high-density sites.The dry matter of cyanobacteria in Meiliang Bay was about 396 tons within the surface 20 cm in the day of sampling.The average daily salvage only accounts on 8.8%of surface cyanobacterial biomass stock.The total fresh biomass of algal bloom entering Liangxi River for three months during the summer cyanobacterial bloom period in Meiliang Bay was 9733 t,which was similar to the amount harvested from the entire lake throughout the year.At present,the salvage ability can only remove a small amount of cyanobacteria biomass that floating on the surface water;the removal ability of the cyanobacteria blooms in the lake is limited.Therefore,the bloom cleaning engineering should be in situ emergency control method when the cyanobacteria gathers.3?Lakes plagued with cyanobacterial blooms have a great impact on the water quality of surrounding rivers.The flux of water bloom particles to the river varied widely,ranging from 75496 t·d-1,with an average of 105 t·d-1.The flux was primarily controlled by hydrological and meteorological conditions.Water volume,temperature,and wind direction were the most important influencing factors.Lake water with a large amount of cyanobacterial particles entering the river can significantly improve the dissolved oxygen,ammonia-nitrogen and phosphorus in the river,while it had a relatively weak effect on dissolved nitrogen and phosphorus.Spatially,the chlorophyll a concentration rapidly decreased with increasing distance from the lake,and the concentration of nitrogen and phosphorus exist as particulate cyanobacteria also declined.Although the connection between rivers and lakes can effectively relieve black spots and solve the black and odorous phenomenon in urban rivers,it had a great impact on nutrients.4?The bloom cleaning engineering and algae water separation stations in the estuary area of the lakeside increased the risk of black bloom disasters.The large amount of cyanobacterial blooms in the salvage point caused the concentration of nitrogen and phosphorus nutrients in the surface water to increase,even more affected the water quality.The remaining cyanobacteria granules sink to surface sediment during autumn and winter increasing the nitrogen and nutrients and organic load of surface sediments,which provide sufficient endogenous supply potential for the occurrence of black blooms.Therefore,delayed salvage will take a risk of black blooms outbreak.Based on above researches,the following suggestions are proposed.?1?To clarify the function of cyanobacteria water salvage,that is mainly used for prevention and control algal bloom excessive accumulation in the coastal belt.?2?Scientifically manage the operation of the pumping station of cyanobacteria bloom lake that connecting the river channel is important.Depending on the different protection targets of rivers and lakes,lake water blooms and hydrometeorological factors should be considered during water transfer management to optimize the water ecological services of lakes and rivers.?3?Strengthen the management of sediments and water quality to avoid new black booms risks and standard-exceeding of water quality,which is caused by bloom cleaning engineering and algae water separation stations in near waters.The research results provide a scientific basis for black blooms warning and cyanobacteria blooms control with the characteristics of water pollution control practice in China. |
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