Mosquito Breeding Status And Cause Analysis Of The Urban Water-green Combined System

Urban water-green combined systems?UWCS?play important roles in society,economics,ecology relying on urban water bodies and green space,the synergy of which produce the sponge effect that is also an essential foundation of sponge city construction.Meanwhile,UWCS are considered to be the breeding places for mosquitoes,and under the overall background of urban ecological changes,mosquito breeding rules has been regulated to some extent,but few attentions were payed to this field.With the support of National Natural Science Fund Project The Research on Coordination Relationships between Urban River Water Environmental Restoration an Mosquito Breeding?51278192?and the special fund for talents of Putuo district The Environment Restore and Secondary Disaster Control of Urban Rivers,10research areas were set up in Shanghai and Chizhou.Through the investigation and analysis of water quality,non-water quality and mosquito breeding status,the caused were explored and the prediction model was established.This paper not only provides supplement and expansion for the cross-research of urban environment and public health,but also the reference for the addition of mosquito control to the planning and design of UWCS and sponge city.It was found that:?1?According to the cluster analysis of water quality conditions,the sample sites can be divided into six categories from good to bad.According to the cluster analysis of non-water quality conditions,the sites can be divided into eight categories based on the light intensity,vegetation coverage,natural enemies,water permenancy and water depth.?2?Although the Gongye River,Xiaozhai River and Henggang River have been treated in 2017 successively and the water quality has been improved in a short time,the concentration of pollutants in the rivers was high due to the inadequate long-term effectiveness of the measures.The drainage system of the outer-ring greenbelt is concealed,with poor sanitation,garbage accumulation and sewage discharged from sanitation truck cleaning wastewater,where the water quality was the worst.While the concentration of pollutants in the secondary effluent of the Shanghai East District Water Plant reached the discharge standard,it still far exceeded the surface water V standard.Therefore,these sites were in the category of inferior V class,but that of the wetland pool and the annular outlet flume was better,which was in the category of III-IV standard,indicating that the constructed wetland had good performance of advanced treatment for effluent.And the others were V class and better.?3?Mosquito larvae were found in the riparian zone of Changfeng Park,the drainage system of west outer-ring greenbelt,the constructed wetland of East District Water Plant and the rainwater pool of Chizhou No.1 High School in 2017,most of which were Culex pipiens pallens and few Armigere obturbans.Mosquitoes in Shanghai mainly breed in late spring and early summer,during which the peak period of Changfeng Park is April,with less dense.The drainage system of outer-ring greenbelt had the highest mosquito larvae density,which can reach 157.6 per spoon.The mosquito larvae of East District Water Plant were mainly found in the inlet and outlet flume of wetland C.The emergence of mosquito larvae in Changfeng Park was the earliest,because the overwinter form of Culex pipiens pallens was fertilized adult mosquitoes.When it gets warmer,they could suck blood and then lay eggs.Therefore,the mosquito in Changfeng Park with sufficient blood resources appeared earlier.A small number of Culex pipiens pallens larvae were found in rainwater pool of Chizhou No.1 High School from June to August 2017.?4?Combining the cluster results of water and non-water quality of samples sites with the mosquito breeding status,it can be found that the presence of mosquito larvae was mainly determined by the non-water quality conditions,while the density in positive samples changed with the water quality conditions.Logistic regression analysis of non-water quality and mosquito larvae also confirmed that the risk of mosquito breeding was lower in water with high light intensity,low vegetation coverage,natural enemies,temporary or permanent accumulation and low depth.Water with high begetation coverage,no natural enemies,semi-permanent acculation and deep depth had higher risk of mosquito breeding,among which OR?odds ratio?of light intensity and water depth is significant?p<0.05?.Water quality conditions affected mosquito larval dentity.The density increases when the water gets dirtier.According to the correlation analysis between water parameters and mosquito larval density,the density was significantly positively correlated with TP,DP,NH₄⁺-N,TN,BOD₅,TOC and COD_Mn?p<0.01?,and negatively correlated with DO?p<0.01?.Increased concentration of pollutants could provide abundant feeding resources for mosquito larvae,hinder the survival of natural enemies,which was beneficial to larvae.Therefore,the larval density in the sampling sites with shade,poor sanitation and water quality but without natural enemies was significantly higher than that in other sites?p<0.05?.?5?Establishing a decision tree?CART?model can better predict the distribution and density of mosquito larval breeding,so that the relevant preventive and control measures can be taken early.The classification tree that predicted whether mosquitoes bred,took natural enemies as root,which indicated that the presence of natural enemies is an import factor affecting mosquito breeding.Under the condition of natural enemies,no mosquito larvae will be found,otherwise it should be determined by Chl.a,light intensity,water depth,TP and DO,with 93.8%CCI?correctly classified instances?and 0.667 Kappa statistic.Two regression tree models were obtained by adjusting variables.Model A took TP concentration as root and generated8 regression equations?LM1-LM8?under different TP,water temperature,COD_Mnn and pH conditions.The correlation coefficient of this model is 0.708.The Model B took BOD₅ as root and had 4 regression equations?LM1-LM4?under different BOD₅,pH and Chl.a concentration.This model was simpler with higher degree of fitting.