Assessment Of Ecological Security In 'One-hour Economic Circle' Of Chongqing Municipality

Ecological security is vital to national security and social stability, with the same importance as national defense, economic security and financial security. It is also the precondition and basis of rapid and stable economic development or even sustainable development. With the rapid population growth and economic development, the conflict of human and land relations becomes increasingly intense because the expanded extent and intensification of human activities disturb environment. The negative effects are as follows:environment degradation and ecological destruction caused by excessive development and overuse of natural resources; loss of living space for human being's survival and development; growing population attacked by ecological disaster and extreme environmental events. As a result, it is possible to endanger the stability of society and threaten the security of regional and national development. Fortunately, people's consciousness on environment protection has been aroused by long-term gaming of ecological security and economic development. Friendly and harmonious eco-environment can sustain the development of economy, society and nature. Both the human survival and social economic development needs more ecological land to ensure ecological security, which require high standards in ecological protection and construction. Thus much attention will be put on ecological security in the long run. However, there lack systematic theories and methodologies of ecological security study, and especially lacks long-term experience of the study in China. Existing researches have been conducted on regional (such as dry area in the western China) or urban ecological security, based on related theories including landscape ecology, conservation biology, disturbance biology, restoration ecology, biological economics, compound ecosystem theory and ecological ethics and so on. Nevertheless, most studies focus on the theories and concepts of ecological security instead of assessment, early-warning and adjustment of ecological security. Consequently, the fruits and application of ecological security studies in China lag behind those in the Western countries.In order to fill in the gaps, this dissertation aims at further the study of ecological security, taking a case of Chongqing Municipality. Chongqing is located in the upper branch of Yangtze River and the center of Three Gorge Reservoir, which indicate that ecological security in the municipality is important for whether local places or the whole nation. On the one hand, the Chongqing's ecological security is the requirement for the national strategy positioning since its unique function in the national development. On the other hand, it is necessary in ecological security and sustainable development for the middle and lower branches of Yangtze River and Three Gorge Reservoir. Chongqing is characterized by diverse landforms and distinct regional difference, which results in the variations of ecological and economic functions in different zones. Especially, the metropolitan area as'one-hour economic circle'is named after the one hour accessibility by public transportation, including 23 districts and counties around the urban built-up-area of Chongqing. This area is featured by highly intense conflict of economic development and ecological security, as well as prompt land use/cover change, considering its function as industrial and urban center. Thus'one-hour economic circle'was selected as a case in this study. The main data sourced from time series of remotely sensed images. Supervised classification and manual interpretation methods were employed to map land use/cover change. Based on the database, classical statistics, spatial analysis of Geographic Information System and geo-statistics were used in the study of ecological security which was reflected by land use change, soil and water erosion dynamics, urban heat island between 2000 and 2008. The comprehensive assessing model and its index system were established in'one-hour economic circle'for the purpose of exploring spatial pattern and evolving trend of ecological security, which aimed at providing suggestions for the better of regional ecological security.The main results are as follows:1. The characters of land use changeFirst, cultivated land in this area decreased but dominated in all land use types between 2000 and 2008, since the ratio of cultivated land area to the total land area changed from 65.44%to 61.07%, with a decrease of 20.47% and 1251.14 km2. The conversion between paddy field and dryland amounted over 50%, and the amount of other land use types converted to dryland was in the first or second rank in all conversion types. The increased forestland came from original pasture, cultivated land, rural residential and industrial land. The increment of residential land and industrial land were mainly converted from unused land with a maximum conversion rate of 106.05% and a minimum of 0.32%. The comprehensive land use dynamics was as high as 0.96% in the period. The absolute change value of K coefficients ranked in descending trend:residential land and industrial land, pasture, unused land, paddy field, dryland, forestland, waterbody.Second, other land use types apart from forestland and pasture largely distributed in the areas with altitude below 800 m. The conversion rate of land use types is higher in low-altitude areas than high-altitude areas. The conversion of paddy field to dryland occurred in Nanchuan, Qijiang and Wansheng, and the conversion of paddy field to residential land and industrial land took place in the main center of Chongqing. The loss of dryland mainly distributed in Changshou, Fuling and Yongchuan. Dryland converted to forestland on the edge of the mountains including Jinyun Mountain, Zhongliang Mountain, Tongluo Moutain. The land use degree began to decrease in Shapingba, Nan'an, Yuzhong, Yubei in the main center, while it increased in Yongchuan, Jiangjing, Fuling, Nanchuan in the outer counties.2. The characters of soil and water erosionThe types of soil erosion in the study area were dominated by micro, slight and moderate erosion. Soil erosion had been effectively controlled in most counties by the implementation of controlling projects in that severe soil erosion converted to slight one. The ratio of micro, slight and moderate eroded land area to the total area increased from 93.56% in 2000 to 95.24% in 2008, among which the ratio of micro erosion increased by 18.99%, though the ratio of slight one decreased by 3.86%, that of moderate one decreased by 13.46%, that of intense one by 1.64%, that of severely intense one by 0.03%, and that of extremely intense one by 0.01%. The spatial results showed that soil erosion was controlled in nine districts of the main center, since most of slight erosion had been converted to micro one. At the same period, extremely and intense erosion were converted into moderate and slight one in Dazhu, Tongnan, Beiei.Soil erosion took place mainly below 1500 m in altitude, and its intensification varied in different altitude. The ratio of eroded area to the total area was more than 95% below 1500 m, among which the ratio was over than 70% for 200-500 m and 500-800 m as a result of intensive human activities and the major types of erosion were moderate, intense, serenely intense and extremely intense one. The area higher than 1500 m covered with high-density vegetation and had only micro or slight erosion. Most of intense erosion located in the area of 200-500m in 2000, and it located in the area of 500-800 m in 2008, which resulted in less erosion in the area below 500 m. The extremely intense erosion increased in the area of 200-500 m and was up to 52.54%. In terms of sloping grade, the area with soil erosion increased with ascending erosion intensification between 0°and 5°; the area with all kinds of soil erosion had no big difference for 5-8°and 8-15°; the area with intense and extremely intense soil erosion located over 15°. The area of extremely intense erosion decreased from 3.417 km2 in 2000 to 0.71km2 in 2008 for the whole study area, but it increased by 11% for the area in 0°-5°and by 5% for the area in 25°and above. The area of extremely intense erosion decreased from 83.57% to 75.14% in 8-15°in the period, and decreased by 10.32% in 15-25°.3. Spatial-temporal characters of urban heat island changeThe overall distribution of urban heat island was described as'Three zones and two belts', that is, The Main Center Zone, The Northwest Zone and The Northeast Zone in Chongqing, as well as The West Economic Belt, The Yangtze River Belt. The prominent urban heat island located in the boundary between the north of Tongliang and the southwest of Hechuan. The high land surface temperature zone was found in the economic developed area along the River. The low, inferiorly low and secondly low temperature distributed in the southeast of Chongqing, including the middle and low altitude mountains in Nanchuan, Wansheng and Qijiang. All kinds of temperature area were stable in the study area between 2000 and 2008. The high or middle temperature area increased slightly, and inferiorly high temperature area decreased slightly, but the low and secondly low temperature area seldom changed. This reflects that there had no apparent change in urban heat island effect in the period.4. Spatial-temporal change of ecological security patternEcological security assessment employed 24 indices based on'background-pressure-status response' model in'one-hour economic circle' of Chongqing. The weights of these indices were obtained using Analytic Hierarchy Process method. The quality of environment was divided by the line along the northeast and southwest in the period. The area in the right of the line had better quality of environment, such as Changshou, Fuling and Jiangjin, but the area in the left was in the contrast such as Tongnan, Dazhu, Tongliang, Rongchang, Yongchuan. The average value assessed was 62.95 in 2000 and 64.73 in 2008, respectively.Ecological security values seemed like the normal distribution in 2000, with peak values of 60,65 and 69, whereas it distributed as multi-peak pattern in the early-warning zone, less secure zone and not secure zone in 2008, and rose in trapezoid shape in more secure zone or secure zone. Above all, the area with security increased apparently.The value of ecological security change was divided into seven zones. The results show that the overall value increased. The reasons for this were that the area with improved value exceeded that with deteriorated value; the area with slightly and notable deteriorated value occupied 19.13% of the total area; and the area with slightly and notable improved value accounted for 43.2% of the total. This reflected positive effects of environmental improvement between 2000 and 2008.Study on ecological security requires complex and systematic methods. The ultimate goal of this kind of study is to realize sustainable use of nature resources and the whole ecosystem as far as possible, and eventually to lay foundation for sustainable development of society and economy. The ecological security study should be effective only if natural resources in regional and surrounding areas can be used in a stable, harmonious, ordered and sustainable way, under the constrains of population growth, social economic development and eco-environment protection.