基于千年生态系统评估对生态系统服务的分类方法，将天津市地下水生态系统服务功能划分为供给、调节、 支持和文化 4 个方面，以此为基础建立地下水生态系统服务价值评估指标体系，采用价值量评估方法构建货币化 的价值评估模型，对地下水生态系统服务价值进行测算，并重点分析南水北调中线工程通水前后天津市地下水生 态系统服务价值演变特征。结果表明：2008—2019 年，天津市地下水生态系统年均总服务价值为 83.71 亿元，其 中，南水北调中线工程通水前（2008—2014 年）为 69.81 亿元，通水后（2015—2019 年）为 103.18 亿元；通水后，地 下水调节服务价值、支持服务价值增大，供给服务价值减小；南水北调中线工程对地下水生态系统服务价值的贡 献呈增大趋势，由 2015 年 2.64 亿元增加至 2019 年 24.01 亿元。

Groundwater is an important water source for maintaining the health of the ecosystem, and it has an essential service value for ecosystem. There are more studies on the service value assessment of ecosystems such as rivers, wetlands and forests, while the study on service value assessment of groundwater ecosystems is not systematic. The service value of groundwater ecosystem in Tianjin is assessed with a view to providing a technical reference for the sustainable management of groundwater ecosystem. In essence, ecosystem service is the benefit for human beings which is provided by ecosystem. Quantitative assessment of the value of ecosystem service could be beneficial to utilizing land resources, protecting water resources and improving the quality of the ecological environment efficiently, meanwhile, it could be an important tool for the human beings to manage the ecosystem rationally. The service value of groundwater ecosystem could be defined as the benefits generated by groundwater ecosystem and ecological processes that contribute to the environment and quality of life for human beings. At present, there are few studies on the service value of groundwater ecosystem, and its assessment index system and assessment methods are still in the exploration stage; previous studies are mostly focused on static assessments. Based on the classification method of the Millennium Ecosystem Assessment for ecosystem service, the groundwater ecosystem service in Tianjin is classified as four aspects: provisioning service, regulating service, supporting service and cultural service. The roles of the service value of groundwater ecosystem could be defined as six aspects: ① the groundwater could supply water resource to life, industry and agriculture, and it could play as the service value of water supply, ② the groundwater could play as the service value of purifying water quality, ③ the groundwater could react with CO2 to generate calcium carbonate, so it could play as the service value of carbon sequestration, ④ the groundwater could play as the service value of water conservation by supplementing and regulating the rivers, lakes and wetlands, ⑤ the groundwater has the function of keeping the geological environment stable, and it could play as the supporting service value, ⑥ the groundwater also has the service value of scientific research and education. Based on this, a index system of service value assessment of groundwater ecosystem is established. Then, a monetized value assessment model is constructed by the value evaluation method. According to this model, the groundwater ecosystem service value in Tianjin is measured, and the evolution characteristics of groundwater ecosystem service value before and after the water supply of the middle route of South-to-North Water Transfer Project(MRP) are analyzed. The result shows that, during 2008 to 2019, the average annual service value of the groundwater ecosystem in Tianjin is 8.371 billion yuan, including 6.981 billion yuan between 2008 to 2014, and 10.318 billion yuan between 2015 to 2019. After the water supply, the value of groundwater regulating service and supporting service are increased, and the value of provisioning service is decreased. The contribution for the groundwater ecosystem service value via MRP is increasing from 0.264 billion yuan in 2015 to 2.401 billion yuan in 2019.The MRP has effectively increased the amount of available water resources in Tianjin, and effectively curbed the trend of declining of the groundwater, expanding of the groundwater depression cone and increasing of the ground subsidence. As some basic data is difficult to obtain, the methods of data assumptions estimation are used in the process of analysis. The data collection will be strengthened in further research, in order to make the results be more and more accurate.