| Watershed is the main research object of environmental science,and also the focus of such complex issues as regional ecological environment,economic and social development etc.Poyang Lake is the largest freshwater lake in China.It is an important lake in the middle reaches of Yangtze River with the characteristic of water carrying,huff and puff and being seasonal.Its annual water inflow reaches 145 billion cubic meters,accounting for about 15.6% of the Yangtze River.As one of the most important wintering habitats for migratory birds in the world,Poyang Lake,whose wetlands and tidal flats have important ecological value,plays an important role in the ecological pattern of the Yangtze River.In recent years,due to the rapid urban construction process in the Poyang Lake Basin,the ecological environment of the related waters is underdifferent degrees of stress.On the basis of ecology,environmental science,geography,economics and demography,this paper combines the new background of ecological civilization construction,taking the driving factors of urbanization as the breakthrough point,and establishes a four dimensional urban coupled coordination model of "population-land-economy-ecology" from the perspective of time,space,industry and behavior.From the perspective of the structure,process,function and carrying capacity of the "Man-City-Lake" integrated ecosystem,the influence mechanism is analyzed by the hydrodynamic water exchange model,and the influence of the watershed urbanization on the ecological environment is explored from the middle or the micro level,and the operable optimization path is put forward for the urbanization development.The main conclusions are as follows:1.The spatial and temporal characteristics of towns in Poyang Lake Basin are identified in this paper,which analyzes the evolution of urban population,land economy and ecology in the basin in the past 40 years,showing that the urban system of the Poyang Lake basin was basically stable in the balanced development state;The fractal dimension of town was 0.702 and 0.690 respectively,and the distribution was relatively scattered and evenly distributed,and the first urban monopoly was not strong.The whole process of land urbanization in the basin is in a spiral rapid growth situation,the spatial development is not balanced,the gap between cities,cities and counties,counties and counties is increasing,and the structure of land use has also changed greatly,the urban construction land has been increased by 1.97%,and the area of water area has been reduced by 1.53%.The economic space center of the basin has gradually migrated from the south of Jiangxi to the central Jiangxi and the northwest of Jiangxi;the economic structure has changed from agriculture to the secondary and tertiary i industry to the urban economic structure.2.Research on the driving factors of urbanization process in the Poyang Lake basin,By constructing impact factor analysis models for population urbanization,land urbanization,economic urbanization and ecological urbanization,etc.,and by analyzing the whole factor model and key factor model,the research on the driving factors of urbanization in Poyang Lake basin is carried out.It shows that(1)the change of population urbanizatioiaon level has obvious linear relationship with the average per capita GDP,the secondary industry value index,the level of land urbanization,the labor productivity of the secondary industry,the labor productivity of the tertiary industry and the employment index of the secondary industry,and the development level of the secondary industry is the key factor for the urbanization of the population.(2)The development of non-agricultural industry is one of the key factors that affect the process of land urbanization.The development of non-agricultural industry is the core power of urbanization.The proportion of non-agricultural industry and the proportion of the tertiary industryis an important factor.Geography also plays an important role.When L≤1,latitude,terrain undulation,elevation and other geographical elements all have obvious correlation with the process of land urbanization;when L > 1,latitude and other geographical factors also have a significant correlation with the land urbanization rate.(3)The spatial evolution of economic urbanization in the basin is significantly correlated with the spatial distribution of five indicators,including GDP per capita,land area per unit of built-up area,output value of 100 million yuan,output value index of primary industry,employment index of secondary industry,and employment index of primary industry.Per capita GDP is becoming a key factor affecting its economic urbanization level.(4)Industrial electricity consumption,retail sales of social consumer goods,land area output value of unit built-up area and bus travel,and the emission of industrial sulfur dioxide is the core factor of the spatial evolution of ecological urbanization.3.The mechanism of urbanization on the ecological environment of Poyang Lake is discussed.By constructing the coordination and coupling model of "population-land-economy-ecology" urbanization in the basin,quantitative analysis and research are carried out.From the aspects of urban population growth,urban industrial structure change and land use pattern change,this paper discusses the impact of urbanization process on the ecological environment of poyang lake.The hydrodynamic water exchange model is constructed from the aspects of the urbanization process on the lake body morphology and pollution sources to analyze the migration and differentiation characteristics of pollutants in the water area and the mechanism of the urban process on the ecological environment of Poyang Lake.The research shows that :(1)the urban integrated system in the basin presents an optimization trend of linear growth in time and gradually enters a critical state;The spatial difference is obvious higher in northern of Jiangxi and lower in southern of Jiangxi.Each subsystem of the basin also showed linear growth,and had obvious stage driving characteristics.It is gradually transiting from economic urbanization to ecological urbanization.At present,land urbanization is the dominant stage,and its sub-system indexes are 0.913 and 0.926.(2)Urban development of river basin has an impact on surface runoff,water area and shoreline,and shoreline geometry tends to be more simple and linear,which has a negative impact on pollutant migration and transformation process and self-purification function of water.(3)the water exchange rate in Poyang Lake area is slow,and the flow rate in the northern lake area is generally higher than that in the southern lake area.In the southern part of Duchang County,the eastern lake bay in the northern part of Poyang County,the marginal water bodies of some floodplain and artificial floodplain in the southern part of inner lake are affected by low flow velocity,and the water exchange capacity is extremely poor.(4)Nitrogen and phosphorus pollutants entering the lake of Ganjiang River basin with a high urbanization level are the main sources of pollutants in the water body of the lake area during the wet season;The water exchange capacity,pollutant retention time and water quality of the eastern lake are poor.4.The impact of urbanization on the ecological environment of Poyang Lake is analyzed.The paper studies watershed ecosystem and water environment quality from Heavy metals,a typical representative of persistent toxic pollutants,were selected as the analysis objects.The surface sediments or surface soil collected in the river inlet,the northern lake area of the inner lake and the surrounding wetlands in the flood and dry seasons were selected as the representative to analyze the impact of urbanization on the environmental quality.Research shows that(1)urbanization process has a great impact on mudflat wetland,water resources,biological chain and other aspects;The urban construction encroaches upon the land in the river basin,leading to the increase of flood,landslide,debris flow and other disasters.Total urban water consumption maintained a linear growth,increasing by 42.3%.Urbanization also leads to the decrease of biodiversity and the stress on the security of the biological chain.The accumulation of heavy metals and other toxic and harmful substances in the water and sediments has a relatively serious ecological stress on the watershed ecosystem.(2)The heavy metals in the southern stations of the study area are relatively high,and the lake river input is one of the main sources of heavy metals in the sediments.Sediments as Zn,Cu,Cd,Pb,Ni and Co in the average contents of these elements in the wet season and the dry season were higher than the background value,in which the quantity of Zn element in the wet season and the dry season is 13.6 times and 15.0 times higher,Cu element is higher,respectively 11.4 times and 10.3 times,Pb element is higher,respectively 4.7 times and 4.3 times,Ni elements is higher,respectively 5.0 times and 5.7 times,Cr element respectively is 1.1 times and 1.8 times higher.5.Put forward to have maneuverable optimized path to town development.The article from industrial space reconstruction,cultivating industrial cluster,perfecting the social support system to establish the interactive development mechanism of urbanization and industrialization;From the regional environmental comprehensive system,environmental capacity and the change of environment self-purification ability of dynamic set up regional ecological environmental dynamic control system;From the ecological environment management plan as a whole mechanism,evaluation mechanism,operation mechanism and so on to establish watershed environmental management mechanisms;From environmental management monitoring,the monitoring of land ecological functions,ecological environment aspects such as establishing digital urban operation system suggestion. |
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