Research On Ecological Security Pattern Of Nanjing Based On Ecological Service Function

With the acceleration of urbanization in China, the large-scale expansion of the city has caused the dramatic changes of the landscape structure. A large amount of woodland,grassland, wetland, farmland and other natural landscape was transformed into artificial landscape. Irrational land development accelerated the interference and occupation of natural ecosystems, which caused a series of ecological problems, such as urban heat island, environmental pollution and ecosystem services decline rapidly. Especially in recent years,haze was more frequently observed in Beijing-Tianj in-Hebei metropolitan region, Yangtze River Delta and Pearl River Delta, which seriously affected people's living standard and threatened the regional ecological security. The academic and government decision-making departments are currently facing severe challenges to how to study on the interaction of landscape structure, ecological process and landscape function on the landscape scale from the view of landscape ecology, and make scientific response to mitigation measures to ensure the safety of urban ecology.Under the background of the degradation of ecosystem services and environmental pollution from water, and air, etc. caused by rapid urbanization, this paper started with the change of ecosystem structure, and studied the evaluation and construction methods of biodiversity conservation service function, water conservation function, flood storage function, water purification function, ventilation and heat displacement function, separately.Based on that, we analyzed the characteristics of the spatial and temporal variation of these functions in Nanjing, and constructed the pattern of biodiversity security, water security and atmospheric security. Moreover, we constructed the comprehensive ecological security pattern of Nanjing City, and put forward the ecological control measures. These would have important guiding significance to maximize ecological service function and slow down many environmental problems in Nanjing.The main research contents and results are as follows:(1) Study on the evaluation and construction of biodiversity security pattern.Evaluation method of biodiversity security pattern was established using In VEST mode and LCP Minimum cumulative resistance model for reference. Based on that, high value area of habitat quality evaluated by In VEST model was used as the "source" of the security pattern of biodiversity, and the corridor and node were established to construct the security pattern of biodiversity by the least resistance surface model. The result showed that the quality of the ecological environment decreased in Nanjing in the past 25 years. The areas of severe habitat degradation were constantly expanding from the urban centers and a habitat degradation circle was formed with a city as the center and the road for the radiation. The proportion of severe degradation and violent degradation was rapidly risen in last 25 years from 2.53% to 8.3%, and 0.65% to 3.83%, respectively. The high value range of resistance area was also expanding. The corridors between Purple Mountain in central city, Fangshan in Jiangning District and other main ecological sources were obstructed completely. The ecological corridors between Anji mountain-Tanshan, Dalian Mountain, Laoshan, Niushoushan and other ecological sources have been seriously threatened. The low, medium and high levels of biodiversity security pattern were accounted for 23.63%, 41.59% and 57.53% of the total land area, respectively.(2) Study on assessment and construction of water ecological security pattern. The water conservation function evaluation model was established through synthetical consideration of the types of land cover, vegetation cover and slope factor. The different frequency of rain and flood disasters risk sensitive areas were identified to establish the different levels of safety of flood storage security pattern by the "non-source flood" theory.Appropriate width of water purification function of different rivers was studied using the Water purification module of InVEST model. We used the high value area of water conservation function area as the source of the water security pattern, and constructed the water safety pattern by the identification of rain and flood disasters risk sensitive areas.The result showed that the area of forest land and wetland did not change very much. The biomass and high value area of water conservation function were increased because of woodlands protection. Moreover, urban construction land occupied a large number of cultivated lands, which caused the median value area of water conservation decrease and the low value area of water conservation increase significant. From the city's point of view,the water conservation function in Nanjing did not destroy very much. The proportion of construction area in rain flood disaster sensitive area in ten year, twenty year and fifty year return periods were increased significantly in study period. Compared to 1990,the construction areas of these return periods in rain flood disaster sensitive area were increased 1.7, 1.37 and 1.28 times, respectively. The construction areas in rain flood disaster sensitive area increased mainly in Banqiao town, Binjiang town, Jiangbei vice city and Longtan port area along the Yangtze River. The Donghsan vice city and Lukou in Jiangning district along Qinhuai River and part of coastal area in Chuhe River increased faster. The construction area in rain flood disaster sensitive area would harshly affect the discharge capacity of the city and threaten city safety. The research showed that the low,medium and high levels of water ecological security pattern were accounted for 23.54%,40.75% and 51.94% of the total land area, respectively.(3) Study on the evaluation and construction of atmospheric security pattern.Meteorology theory, city morphology theory and application of remote sensing technology were combined to study the evaluation and construction method of atmospheric security pattern based on ventilation corridor. Through the research of remote sensing technology of thermal environment in the city spatial difference, according to the meteorology City Local Circulation Theory and city morphology theory,on the basis of windward area index and surface temperature to build city ventilation resistance surface, the urban ventilation corridor was constructed using LCP (least cost path) technology. The feasibility of using remote sensing technology and GIS technology to study the ventilation corridor was verified based on WRF(weather research and forecasting model), CFD(computational fluid dynamics model) and observation data from meteorology and field. The research showed that ventilation corridors at the scale of the city mainly located in wide river, lake and valley land, which illustrated that these areas not only had the functions of biodiversity conservation, flood storage and water purification, but also had good Heat ventilation function. On the block scale, in addition to wide rivers and lakes as the main ventilation corridor outside,broad streets to the direction of the wind were also main ventilation corridors.(4) Construction and Countermeasure of comprehensive ecological security pattern.On the basis of the biodiversity security pattern,the water security pattern,the atmospheric security pattern, the urban ecological security pattern based on multi-factors of ecological service was constructed. The research showed that in Nanjing the total area of high level ecological security pattern accounted for 65.67% of the land area of the whole city, which illustrated that, most land in Nanjing had a significant ecological function. The low level ecological security pattern accounted for 30.03% of the land area of the whole city, which illustrated that, these lands in Nanjing had an important and irreplaceable ecosystem service. On this basis, proposed ecological protection strategy for ecological security can better guide the urban ecological environment planning and management, and promote the improvement of urban ecosystem service function and environmental quality.Major innovations of this thesis:(1) This paper comprehensive considered the development trend in meteorology,ecology, city morphology in the ventilation corridor, biodiversity research, water ecological security pattern to study the ecological security pattern in an interdisciplinary research area.(2) On the basis of the biodiversity security pattern, the water security pattern, we constructed the atmospheric security pattern and urban comprehensive ecological security pattern to provide a new idea and method for study on urban ecological security pattern.