Research On The Water Quality And Trophic State Of Typical Lakes And Reservoirs In Kunming

Kunming’s lakes and reservoirs play an important role in carrying the history and culture of the spring city,regulating the microclimate of the city,constructing the urban landscape as well as creating a livable and pleasant environment.However,with the acceleration of urbanization,urban water environmental quality and heavy metal pollution are serious.Research on water quality and nutrient status of typical urban lakes and reservoirs in Kunming,a plateau city,is helpful to understand the water pollution status and nutrient status of urban lakes and reservoirs.In order to provide basic data and scientific reference for the prevention and control of kunming urban lakes.In this paper,10 lakes located in the center of the city and 11 lakes and reservoirs located in the edge of the city were selected as research objects,and the main hydrochemical indexes of these lakes and reservoirs were analyzed,such as p H,dissolved oxygen,transparency,total phosphorus,total nitrogen,chlorophyll,etc.as well as the contents and distribution characteristics of copper（Cu）,chromium（Cr）,nickel（Ni）,cobalt（Co）,zinc（Zn）and other heavy metal elements in water.The environmental quality of water was evaluated from three aspects: water quality evaluation,nutrient status evaluation and heavy metal pollution evaluation,and the possible sources of heavy metal pollution in urban center and suburb water bodies were discussed by using multivariate statistical method.The main conclusions are as follows:（1）The results of hydrochemistry experiment showed that there were differences in the water chemistry indexes of lakes and reservoirs between urban and suburban areas.It was found that the lakes and reservoirs under study were alkaline as a whole,and the spatial differences of chlorophyll-a,total nitrogen and total phosphorus concentrations were large,while the spatial differences of dissolved oxygen,conductivity and p H at all sampling points were small.TP in all the lakes and reservoirs water within the research scope exceeded the standard,28.57% were V,and 71.43%were poor V.Generally speaking,the water quality of urban lakes and reservoirs are still severe,and the water quality of all the water has not reached the target functional water quality category.The correlation analysis showed that the correlation between the percentage of urban land-use type and water quality index was weak,but the correlation between the percentage of suburban land-use type and water quality index was strong.（2）The evaluation of comprehensive pollution index and comprehensive trophic state index showed that the lakes and reservoirs were polluted and eutrophic.The results showed that most of the comprehensive pollution index of lakes and reservoirs water bodies evaluation belong to mild pollution,and a few belong to heavy pollution and serious pollution.All the lakes and reservoirs water bodies in the urban area were polluted and eutrophic,91 % of the lakes and reservoirs water bodies in the suburb were polluted and 9 % of the lakes water bodies were clean.In the lakes and reservoirs located in the suburb,91 % of the water is eutrophic and 9 % is moderate.On the whole,the urban lakes and reservoirs water bodies in Kunming were seriously eutrophicated.（3）The concentrations of copper（Cu）,Chromium（Cr）,nickel（Ni）,cobalt（Co）,zinc（Zn）,arsenic（As）,Molybdenum（Mo）,cadmium（Cd）and lead（Pb）detected by atomic absorption method for 21 lakes and reservoirs did not exceed the national surface water environmental quality standard value of Ⅳ.Except for the chromium（Cr）concentration close to the national surface water environmental quality standard value of Ⅳ,the concentration of other metal elements all belong to the national surface water quality level Ⅰ,so the overall situation is relatively optimistic.Nemerow comprehensive pollution index method was used to evaluate the concentration of heavy metals in lakes and reservoirs.The results showed that all the lakes and reservoirs were not polluted by heavy metals,but Majinputang reservoir was at risk of being polluted.（4）Multivariate statistics were used to analyze the main sources of heavy metal pollution in lakes and reservoirs,including urban sewage and industrial and agricultural wastewater.The heavy metals Cr,Ni,Cu,Zn,Cd and Pb of lakes and reservoirs water bodies in urban areas appeared in the water samples collected from Cuihu lake and Lotus Pond,and their pollution sources were mainly urban life discharge sources.However,the high values of Co and As appeared in Muchun Lake and Luolong Lake,and the pollution sources were mainly industrial and agricultural pollution.The main sources of Mo pollution in urban lakes water bodies were industrial waste water and electronic equipment waste.The heavy metals Ni,As,Mo,Cd and Pb in the lakes and reservoirs water bodies in the suburb of Yunhu,Majinputang and Bailongtan reservoirs had large values,and the pollution sources were mainly agricultural and traffic pollution sources.Cr and Co elements were found in the water samples collected from the lakes and reservoirs water bodies in Chenggong district.Cu and Zn elements in lakes and reservoirs water bodies in the suburb of the city may be natural sources.