Due to its dynamic stability and good water quality, karst water in the northern region of China has become an important water source for urban water supply, and industrial and agricultural activities, providing an important support for economic and social development. Karst springs in Jinan City are also important natural resources integrated with water supply, tourism and ecology. However, since the 1970s, the karst groundwater mining has increased greatly with the rapid development of urban construction; consequently, four major karst spring groups in Jinan gradually dried up and even incurred the cutoff. Until the early 21^st century, the four major karst spring groups began to gush again, thanks to the implementation of a large number of ecological control measures. But the water quality of these spring groups is not as good as it was before and the flow is also not large as before. Moreover, there exist ecological and environmental issues such as water quality deterioration, water flow decline, etc. Scholars from around the world have conducted much hydrogeological research in Baotu Spring basin, including the source of recharge of karst groundwater, the cycle of evolution, the relationship between karst cold water and northern geothermal energy, the spatial distribution of karst water-bearing media and flow field characteristics, the conversion relationship of karst water and surface water, etc. However, it is difficult to accurately grasp preponderant runoff paths in karst aquifers at a scale of the hydrogeological unit, which is one of most difficult challenges in the study of karst groundwater. oundwater.

The authors are convinced that the analysis of preponderant runoff paths of karst groundwater is prone to be not precise, due to the limitation of spatial accuracy at a scale of the hydrogeological unit. Therefore, in order to clarify the main preponderant runoff paths near the four major karst spring groups in Jinan, and to protect the spring water resources in a more scientific and reasonable way, this study chooses the local area near the outlet of the karst springs as the object, analyzes the preponderant runoff paths of the four major karst spring groups in Jinan, and calculates the contribution ratio of the preponderant runoff paths for each karst spring group by using quantitative analysis of flow velocity and flow direction, groundwater flow field analysis, hydrochemical isotope analysis, cluster analysis, and calculation of the mixing ratio of the three-terminal elements.

The study shows that the preponderant runoff paths of the four karst spring groups can be divided into the western, southern and southeastern preponderant runoff paths. Among these paths, the southeastern preponderant runoff path mainly comes from the karst groundwater recharge in the runoff area on the east side of the Qianfo mountain fault; the southern preponderant runoff path mainly comes from the karst groundwater recharge in the runoff area on the west side of the Qianfo mountain fault; the western preponderant runoff path mainly comes from the karst groundwater recharge along the contact zone of gray rock and igneous body in the western suburb of Jinan. In general, water chemical components, and hydrogen and oxygen isotope fractions of these four karst spring groups can be devided into two areas in terms of spatial distribution, namely, the east-west strip distribution area of Zhenzhu spring group and Wulong spring group, and the east-west strip distribution area of Baotu Spring group and Heihu spring group, indicating that the four karst spring groups are subjected to a mixture of different preponderant runoff paths. But even so, the main recharge path of every spring group is different. For example, both Baotu Spring group and Zhenzhu spring group are recharged by the south recharge path with the respective recharge flow ratio of 40.21% and 51.04%, Heihu spring group by the east-south path with the recharge flow ratio of 47.42%, and Wulong spring by the west path, with the recharge flow ratio of 47.13%. The research findings can provide references for the formation mechanism and ecological protection of karst springs in North China.