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This study enhances the understanding of the evolution of water transport in karst water flow systems. This paper explores the karst water flow system from a hydrogeochemical perspective. It has been discovered that in the recharge area, the hydrochemical effect of karst water is primarily influenced by dissolution and filtration. In the fault zone and concentrated discharge area, it is primarily influenced by mixing. In the geothermal area, the dominant factors are dissolution, precipitation, and dolomitization. From the southern to the northern area, the hydrochemical type of karst water gradually changes from HCO3-Ca type to SO4·Cl-Ca·Na type. Atmospheric precipitation is the primary recharge source of karst water, with a recharge elevation range of 181–1,495 m. According to geological drilling statistics, the groundwater transport depth transits from the shallow transport in the south to the deep transport in the north, with a depth range of 3,000–3,500 m, and using isotope data to obtain the groundwater retention time range is 6–27,000 years. The groundwater transport mode is divided into three levels: open-shallow transport karst cold water phreatic flow, semi-open-medium-deep transport karst cold water confined flow, and weak open-deep transport geothermal water confined water flow. HIGHLIGHTS This study has revealed the hydrochemical evolution and transport patterns of karst water in the Jinan spring area.; The transport mode of the karst water flow system in the monoclinic structure of the Jinan spring area has been classified.;

Due to the influences of geological structures, many confined ascending springs occur in North China's karst area. The electrical conductivity (EC) of karst spring flow is a fundamental variable in characterizing karst systems. However, deeply exploring hidden nonlinear dynamic characteristics is challenging. To avoid overreliance on the fitting polynomial order in the detrending process via classic multifractal detrended fluctuation analysis (MFDFA), the intrinsic time-scale decomposition (ITD) method was applied to identify the external data trend term by decomposing the original data into different frequency modes, and the ITD-MFFA method was proposed to reveal the formation mechanism of spring EC complex characteristics in Jinan's spring area. The results showed that the EC sequences of North China's karst springs are characterized by multifractal behavior and anti-persistence and exhibit multiyear complexity with an overall decreasing trend. Different recharge sources, formation conditions, and seasonal precipitation could be the primary factors driving spring EC complexity. Compared to those of the traditional MFDFA method, the ITD-MFFA method achieved improved anti-interference ability and stability. Timely determination of spring EC data dynamic complexity and monitoring future spring water quality trends can provide guiding significance for protecting karst springs. HIGHLIGHTS Compared with the MFDFA method, the proposed new approach (ITD–MFFA) improves anti-interference ability and stability.; Multifractal fluctuation feature in karst springs’ electrical conductivity data is found.; The complexity of springs' electrical conductivity is not only affected by many factors but also significantly higher in the dry season than in the wet season.;