Vulnerability assessment of karst groundwater in the Jinci spring area and the zoning of protected areas for water quality

Jinci spring is a famous karst spring in Shanxi Province, and its backflow is an ecological restoration goal of the Shanxi Provincial government. Composed of Nanlao spring, Shengmu spring, and Shanli spring, Jinci spring is exposed at the foot of Xuanweng mountain in the western mountains of Taiyuan, twenty-five kilometers away from the city center, and it is a concentrated discharge point for karst water in the Jinci spring area. Karst water in the spring area is mainly supplied by atmospheric precipitation infiltration and leakage from rivers and reservoirs. Karst water in the Jinci spring area is an important water source for people's life and industrial and agricultural production in Taiyuan City. In recent years, with the intensification of climate change, large-scale development of karst water, coal mining and other human activities, especially after the construction of the second reservoir of the Fenhe river, the karst hydrogeological conditions in the spring area have undergone fundamental changes, with the spring area expanding from 2,030 km² to 2,713 km², which has affected the evaluation, management and protection of karst water resources in the spring area. The original zoning of protected areas can no longer meet the needs of water resource management and protection. Therefore, it is urgent to re-zone the protected areas and formulate corresponding protection measures. In terms of the problems on water quality and quantity, there exist differences in the causes, regions, and protective measures, and thus LIANG Yongping et al. proposed the concepts of "water quantity vulnerability" and "water quality vulnerability", as well as a method of "first classifying, and then grading" for the zoning of karst aquifer protected areas.This study focuses on the hydrogeological conditions of special recharge, runoff, and discharge in the karst water system of North China, as well as the main influencing factors of the antifouling performance of karst aquifer systems. It combines European methods and "water vulnerability assessment" to evaluate the antifouling performance. Based on infiltration duration of karst water in the unsaturated zone, leakage of rivers and reservoirs, precipitation infiltration in different regions, and replacement of karst aquifer media structure with water abundance, this study selects four factors to evaluate the antifouling performance of karst aquifers in North China, including the thickness of unsaturated zone, the amount of infiltration recharge, the lithology of overlying strata, and the water abundance of karst aquifers. Taking the newly divided karst water system in the Jinci spring area as the evaluation object, this study aims to evaluate the vulnerability of karst water system in the spring area and to zone the protected areas.The results show as follows, (1) The protected areas are mainly distributed in Jinci park and its surrounding areas. (2) The first-class protected areas are mainly distributed in the main stream of the Fenhe river, the exposed areas of carbonate rocks in the front of western mountains of Taiyuan, and the leakage sections of carbonate rocks in Tunlanchuan, the Tianchi river and the Liulin river. (3) The second-class protected areas are mainly distributed in the north of the spring area and the north bank of the Fenhe river. (4) The quasi-protected areas are mainly distributed in the south bank of the Fenhe river and the Taiyuan basin in the southeast. The newly zoned protected areas for spring water quality can provide a basis for the rational protection and scientific utilization of karst water resources in the Jinci spring area.