太湖流域水生态服务供需空间量化、格局演变与驱动机制

Changes in land use and land cover of a watershed area dramatically alter terrestrial ecosystem patterns and ecological processes, causing a wide range of water environmental issues. This can be attributed to the imbalance between ecosystem service supply and demand. Therefore, the causes for watershed environmental issues cannot be fully retrieved considering only the supply side of ecosystem services. Based on concepts and principles in the fields of ecosystem service geography and landscape ecology, this project will investigate both supply and demand dynamics of three water-related ecosystem services (i.e., water supply, water purification, and flood regulation) in the Taihu Lake Basin by employing spatially explicit modeling tools and spatial statistical analysis approaches. The project includes the following three parts of study. First, the project will build assessment models and the supply-demand ratio index for quantifying supply, demand, and budgets of the three water-related ecosystem services in the Taihu Lake Basin. Second, this project will identify hotspot regions of supply-demand surplus and deficit for the three ecosystem services at the county level and the sub-watershed level, respectively. The multi-scale dynamics of ecosystem service supply and demand in the Taihu Lake Basin can be revealed through investigation of the spatio-temporal dynamics of these hotspot regions at both levels. Third, this project will explore key driving factors and their spatio-temporal variations for supply-demand dynamics of the three ecosystem services. This project will also propose regulatory measures for optimization of the spatial patterns of ecosystem service supply and demand in the Taihu Lake Basin. This project, by integrating both ecosystem service supply and demand in research, can provide us with a better understanding of the underlying patterns, processes, and mechanisms of ecosystem service dynamics in response to LUCC, and provide new insights into regulating watershed environmental issues.

流域土地利用变化显著改变陆地生态系统格局及生态过程，是导致水生态环境问题的重要原因，其实质是生态系统服务时空供需失衡。因此，仅考虑生态服务供给无法全面揭示流域生态问题的症结。本项目拟综合生态系统服务供给与需求，以太湖流域水生态服务供需格局为研究对象，在生态系统服务地理学和景观生态学相关理论指导下，采用空间定量模型和空间统计分析等方法，构建太湖流域典型水生态服务（水资源供给、水质净化与洪水调蓄）供需评价模型及供需比指数；分别在子流域尺度和县域尺度分析不同水生态服务的供需定量关系，识别供需盈亏的热点区域及时空变化，揭示太湖流域水生态服务供需格局演变的多尺度特征；辨明影响水生态服务供需动态演变的驱动机制因子及时空尺度分异，探讨太湖流域水生态服务供需空间格局优化调控措施。研究旨在深入理解土地利用变化影响下水生态服务演变的格局、过程与机制，并为应对流域水生态环境问题提供新的研究视角和管控途径。

本项目利用土地利用、地形地貌、水文气象、社会经济和InVEST生态系统服务评估模型等多源数据方法，从太湖流域、县域、子流域三种空间尺度分析了水源涵养与水质净化服务供需盈亏关系及时空演变特征。在此基础上，通过综合水量与水质目标，进一步构建了太湖流域水资源供需综合评估模型，依据水资源供需关系将太湖流域初步划分为水资源充沛、水质型缺水、资源型缺水及综合型缺水四类区域，并探讨了流域水安全保障的土地管控策略。本研究发现：（1）1995–2015年间太湖流域快速的土地、人口和经济城镇化过程导致水资源需求占供给量的比重由73%升至90%，依赖外来客水的县域和子流域面积占比由19%升至33%；在极端干旱情景下，太湖流域水资源需求量比供给量为117%，水资源赤字县域面积占比为47%，赤字子流域面积占比为41%。（2）1995–2015年间太湖流域建设用地扩张挤占了氮磷排放量最高的农业用地，流域整体的水质情况略有改善；但同时由于建设用地较高的氮磷污染负荷，以及对林草地的挤占降低了氮磷截留效率，因此水质状况仍不容乐观，有超过75%的县域及子流域接近水质净化服务供需赤字状态。（3）综合水量与水质状况可知，太湖流域水资源充沛区面积占比仅约30%，多分布于太湖西南侧，水质型缺水是太湖流域水资源短缺的重要原因，该类型区多分布于太湖北侧及东南侧，资源型缺水及综合型缺水区多分布于太湖东北侧。（4）基于上述发现可知，太湖流域水资源利用受快速城镇化、气候变化及农业面源污染的多重胁迫，耦合水量与水质目标的水资源供需综合评估及分区管控为流域水资源可持续利用提供了有益参考。