Karst aquifer characterization using storm event analysis for Black Dragon springshed, Beijing, China

• Karst aquifers were characterized to ease a megacity's water shortages.
• Hydrological and geochemical responses of the springshed to 721 Storm identified.
• Spatial heterogeneity of water chemistry of the springshed identified.
• Recharge area of springshed confirmed.
• Springshed water balance and groundwater infiltration evaluated.

Beijing is a megacity suffering from acute water shortage. The characterization of karst aquifers in Beijing's outlying districts is critical to inform sustainable policies and practices in groundwater development. We captured spring hydrogeochemical dynamics during an intense storm event (721 Storm) by installing a data logger in the weir, which presents an opportunity for defining and characterizing the recharging sources of discharge from Black Dragon (BD) springshed. Multivariate techniques (including PCA, 2D-HCA heat map, and piper diagram) were used to characterize the waters and investigate their geochemical evolution. The results in combination with hydrological evidence suggest BD Spring was dominated by interaction with dolomite host limestone rock during dry season, whereas it was fed by a second water supply (dolomite aquifer) during storm events. The infiltration coefficients were calculated based on the water balance model, and it was found that the 721 Storm has resulted in less infiltration due to the high rainfall intensity. We presented a novel methodology, combining high-frequency data sets and routine manual flow measurements with traditional geochemical sampling techniques. This methodology appears to be very efficient at characterizing a karst aquifer and seems to be potentially applicable to other karst aquifers.

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