Attribution Of The Entrophication Change In Xingyun Lake Based On System Dynamics Model

Water pollution is an important environmental problem in today's world.Eutrophication is one of the important manifestations of water pollution.As one of the nine plateau lakes in Yunnan Province,Xingyun Lake plays an important role in the economic and social development of local agriculture,industry,tourism and other industries.However,since the1980s,due to the neglect of environmental protection in the process of economic development,the water quality deteriorates obviously and results in serious eutrophication.In this paper,based on the water quality data and basin statistical data of Xingyun Lake,the trophic status of Xingyun Lake is evaluated by the comprehensive trophic state index,and a system dynamics model of"Xingyun Lake Eutrophication"is constructed based on the system dynamics theory to model the eutrophication change,and then the main driving factors and their contribution to the eutrophication of Xingyun Lake are analyzed.(1)The comprehensive trophic state index and related eutrophication indicators showed an increase trend.the TP increased most significantly among the related indicators,which shown an important eutrophication process of Xingyun Lake.The comprehensive trophic state index of Xingyun Lake showed an upward trend in the whole series,with a short-term decline in 1996-1998 and 2013-2017,and a short-term stable change during 2003-2007.After1997-2008,the comprehensive trophic state index increased rapidly.The change trend of the trophic state index presented by the main indicators of Xingyun Lake is roughly the same as that of the comprehensive trophic state index,which showed an increasing state on the whole.The trend of TLI(TP)is consistent with TLI(?)from 1994 to 2008.After 2008,the trend of TLI(Chl.a)is consistent with TLI(?).(2)Based on the formation process of lake eutrophication and the theory of system dynamics,the system dynamics model of"Xingyun Lake Eutrophication"with five subsystem models of TN,TP,COD_Mn,SD and Chl.a were constructed with the help of Vensim DSS 6.4e software.The model explores the relationship between variables and the transmission mechanism by the drew cause-effect loop diagram and system flow diagram by the according main equations from one indicator to another.The results showed that the system dynamics model of"Xingyun Lake Eutrophication"exhibited a good simulation applicability with an error of within 10%,can accurately reflect the actual situation of Xingyun Lake Eutrophication,and had a certain practical application value.(3)Industrial sewage discharge,urban domestic sewage discharge,livestock and poultry breeding pollution discharge and sewage treatment plant removal changed abruptly in 1997,resulting in a significant increase in the comprehensive trophic state index of Xingyun Lake in1997.Xingyun Lake became an eutrophic lake after 2000,which was related to the increasing trend of rural domestic sewage and tourism sewage after 2000.The change trend of rural domestic waste pollution and agricultural solid waste pollution was abrupt in 2002,which made comprehensive trophic state index of Xingyun Lake fluctuate for a long time after 2002.(4)In the trophic state related indicators and the eutrophication system of Xingyun Lake,the contribution of non-point source pollution is higher than that of point source pollution,which is the main reason for the eutrophication of Xingyun Lake.In terms of the contribution of the driving factors,the contribution of the non-point source pollution increases in the"Xingyun Lake eutrophication"system.From the change of contribution degree of driving factors in subsystems,the contribution degree of driving factors in TP,SD and Chl.a subsystems is obviously enhanced,which aggravates the eutrophication of Xingyun Lake.