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Due to climate change and human activities over the last fifty years, the spring flow volume of karst groundwater has sharply diminished in China. Climate change is one of the critical factors that initiates a series of karst hydrogeologic and water ecological environmental problems, because the precipitation shows a decreasing trend while the temperature shows an increasing trend. The Jinci Spring is one of the largest, most famous springs in northern China. This study employed data from the Taiyuan Meteorological Station and ten precipitation stations in and around the Jinci Spring region as well as the runoff data gathered from two hydrological monitoring stations during 1960-2012. The sliding average method and the Mann-Kendall test were used to analyze the variation tendency of precipitation, temperature, and land evaporation in this area. Finally, the following were calculated: the varying pattern of the karst groundwater recharge amount and the response of the recharge amount to precipitation, land evaporation, and river runoff by quantitative analysis. The results indicated that the precipitation and land evaporation amount decreased at first and then subsequently increased. Likewise, the variation trend of the karst groundwater recharge amount in the spring region was roughly consistent with the precipitation variation pattern. In contrast, the temperature displayed an increasing trend. The climate change resulted in a reduction of the karst groundwater recharge amount, and it had the greatest influence in the 1990s, which caused the karst groundwater recharge amount to decrease 26.75 mm as compared to that of the 1960s (about 39.68% lower than that of the 1960s). The Jinci Spring had zero flow during this period. The reduction in precipitation was one of main factors that caused the cutoff of the Jinci Spring.

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Due to the significance of karst groundwater for water supply in arid and semi-arid regions, the characteristics of the karst groundwater flow system in the Liulin spring area, North China, are analysed through isotopic tracing (δ(2)H, δ(18)O, δ(13)C and (3)H) and dating approaches ((14)C). The results show that the primary recharge source of karst groundwater is precipitation. Evaporation during dropping and infiltration of rainfall results in a certain offset in the values of δ(2)H and δ(18)O in groundwater samples from the global meteoric water line (GMWL) and the local meteoric water line (LMWL). The altitudes of the recharge region calculated by δ(18)O range from 1280 to 2020 m above sea level, which is consistent with the altitudes of the recharge area. The Liulin spring groups could be regarded as the mixing of groundwater with long and short flow paths at a ratio of 4:1. In the upgradient of the Liulin spring, the groundwater represents modern groundwater features and its [Formula: see text] is mainly derived from dissolution of soil CO(2), while in the downgradient of the Liulin spring, the (14)C age of dissolved inorganic carbon (DIC) in groundwater shows an apparent increase and [Formula: see text] is mainly derived from the dissolution of carbonate rocks. The mean flow rate calculated by (14)C ages of DIC between IS10 and IS12 is 1.23 m/year.

Abstract:Exploring the hydrogeochemical processes of karst groundwater has significant meaning for protecting local groundwater systems in semi-arid areas. Taking a typical semi-arid karst groundwater system-the Liulin spring area-as the research region, hydrogeochemical processes from rainfall infiltration to formation of higher total dissolved solids (TDS) water were studied, applying a mass balance model and the prediction of water chemical components in the focus area was explored. The results showed that hydrogeochemical processes dominating chemical components of karst groundwater included lixiviation, cation exchange and mixture. Calcite dissolved during rainfall infiltration processes in recharge area and saturated, then precipitated along the whole flow path. CO 2 dissolved significantly along with rainfall infiltration process and outgassed in discharge area and stagnant area. The dissolution of dolomite, gypsum and halite accompanied entire flow path and maximum dissolution load occurred in stagnant area. Mg-Na or Ca-Na exchange prevailed along flow path but exchange types depended on ionic concentration. The mixture between surface water and karst groundwater took place in surface water leakage belt in recharge and discharge area and mixture ratio for surface water ranged from 40% to 70%. TDS of the Liulin springs will increase with decreasing surface water leakage. Conversely, TDS of karst groundwater near Henggou area will decrease accompanied by the continuous discharge of the Henggou artesian well.