Effect Of Measures Controlling Algal Bloom In Beijing Urban Rivers And Lakes

Urban rivers and lakes include natural rivers,canals,channels（including culverts）,lakes,and reservoirs in city.The ecological system of urban rivers and lakes is an important component of the whole urban water ecosystem,and is also an important component of the whole city ecosystem.It is closely related to urban human activities.In recent years,with the rapid development of social economy,the enlargement of city scale,and the increased number of artificial buildings,the urban water system of Beijing has been shrinking,while eutrophication has been getting worse and the quality of water environment deteroiating.This resulted in the decrease of the amount of available water resources and deterioration of the ecosystem of the urban rivers and lakes,and Cyanobacteria blooms have often broken out in the urban rivers and lakes of Beijing.Cyanobacteria bloom is very harmful.It is a threat to the source of drinking water,and can destruct the ecological landscape and surrounding environment,reduce biodiversity,and damage the food chain.Furthermore,the microcystin in Cyanobacteria could directly endanger human health.Through a lot of field investigation and visiting management,construction,design and research agencies,together with collecting and analysing historical data,trends and influencing factors of algae bloom in Beihucheng River during 2007-2014 is both quantitatively and qualitatively studied.This case study is carried out with the study of the ecosystem of the urban rivers and lakes in Beijing as the background.In the study,it is found that the lake water is in a eutrophic state,and condition for algae bloom is in place,and the bloom is almost inevitable every summer.The occurrence of algae bloom include a slow period,rapid growth period,maintenance period and decline period stages.The concept of algae bloom rate can clearly quantify the severity of algae bloom,help analyse the relevant impact factors,and help illustrate the impact on the algae bloom in a year or in multiple years.Water temperature,COD_Mnn and algae bloom rate have a strong positive correlation.The average annual flow and algae bloom rate have a strong negative correlation.River flow in the 0.001-0.01m/s,cannot affect water bloom and early growth,but still have an important role on inhibition of bloom.City rainfall flood,artificial control and artificial water governance is an important factor in the development trend of river water bloom,and other factors are less effective.In order to more objectively evaluate the controlling measures,a simple and objective evaluation method is established.The method is based on the calculation of the chlorophyll-time graph,the introduction of effective removal and the concept of effective removal rate.It takes into account rainfall,annual average temperature,water quality and flow difference.Based on the study,suggestions are given to control algae bloom in urban rivers and lakes.It is believed that to control algae bloom,multiple measures should be utilized,including strengthening monitoring and early warning,control of pollution,better water dispatching,and improvement of management,etc.