1988-2013年重庆市主城九区生态用地空间结构及其生态系统服务价值变化

在当前快速城市化的背景下，理解和把握城市生态系统服务功能退化原因及规律的最有效手段是对其生态用地结构及其生态系统服务价值进行准确的评估。采用RS、GIS技术以及生态系统服务价值评估等方法，对重庆市主城九区1988、1996、2004、2013年4个时段遥感影像进行解译及比较分析，结果表明：1988-2013年间，重庆市主城九区城市化水平经历了加速阶段、减速阶段及饱和阶段，城市化水平的提高对城市建设用地增长的影响显著；重庆市主城九区生态用地主要为城市提供了食物生产、提供原材料、废物处理、土壤形成与保护、气候调节、气体调节、生物多样性以及水源涵养等生态系统服务，在结构变化上呈现出“二减三增”的结构变化特点；25年间重庆市主城九区共减少生态系统服务价值260.60×10⁶元，整体处于下降趋势，其中农地的生态系统服务价值损失最大，共减少24.50%；在空间分布上，随着城市建设用地向“南-北-西”方向扩展，生态系统服务价值以中梁山与铜锣山之间的区域减少最为严重，整个研究区生态系统服务价值下降的主要原因来自于农地的大量减少以及城市建设用地扩张所带来的生态负影响。研究结果表明在重庆市主城九区生态用地空间格局与生态系统服务变化之间存在密切相关性，在城市化率达到饱和阶段后应严格控制建设用地增长，促进建设用地集约节约利用，加大农地的保护力度以及对林地、水体、草地的维护，维持整个区域的生态平衡。研究可为科学合理布局和保护城市生态用地提供信息资料和决策参考。

Changes in the spatial structure of ecological land and ecosystem service values in nine key districts of Chongqing City over the past 25 years

Land-use change is a major factor that drives changes in ecosystem services. Measuring variations in the values of ecosystem services that correspond to changes in land use is an effective way of assessing environmental costs and benefits for environmental policy planning. The present study adopted the above approach in the current context of rapid urbanization, using the nine key districts of Chongqing City (a typical fast-growing Chinese city) as a case study. Conducting accurate assessments of the structure of ecological land and associated ecosystem service values has emerged as the most effective approach for understanding the causes and patterns of the functional degradation of ecological services. Together with accurate spatial datasets of Landsat^TM images from 1988 to 2013, we used remote sensing, geographic information system (GIS) technologies, and ecosystem service value assessment methods to analyze the urbanization levels of Chongqing`s nine key districts. The present study explored variations in the spatial structure of urban ecological land and the effects of different levels of urbanization across these districts on the expansion of urban construction land. The study further assessed changes in monetized values of ecosystem services that were caused by changes in the structure of urban ecological land. The results showed that from 1988 to 2013, urbanization levels of the study districts first underwent an acceleration phase, subsequently shifting to a deceleration phase, and finally reaching a saturation phase. Increased urbanization levels had a significant impact on the expansion of urban construction land. The ecological land in these districts of Chongqing provides a number of ecosystem services, including food production, supplemental raw materials, waste treatment, soil formation and protection, climate regulation, gas regulation, and biodiversity and water conservation. The structural changes of ecological land evidenced a "two minus three growth" pattern. The value of ecosystem services calculated for the study districts revealed a total loss of 260.60×10⁶ Yuan over the past 25 years. The greatest loss was incurred for the value of farmland ecosystem services that showed a reduction of 24.5%. Together with the spatial distribution change, entailing the expansion of urban construction land toward the west, north, and south, the greatest loss in terms of the ecosystem service value was incurred in the region between the Zhongliang and Tongluo mountains. The main reason for the decline in ecosystem service values over the entire study area was the negative impact resulting from farmland reduction and the expansion of construction land. The present study revealed a strong correlation between the spatial pattern of ecological land and changes in ecosystem service values in relation to the different urbanization levels of Chongqing''s nine key districts. Once the urbanization level reach saturation, strict regulations should be implemented to control the expansion of construction land and promote its intensive use. Efforts to protect farmlands, forests, grasslands, and wetlands should be enhanced to maintain the ecological balance of the entire region. This research can provide information and guidelines to facilitate decision-making in relation to the design of scientific and rational layouts as well as urban ecological land protection.