Drips Hydrogeochemical Characteristics Of Furong Cave And Its' Implications

In recent years there has been a growing interest in cave speleothems as archives of paleoclimate change.An understanding of temporal and spatial variability of cave drip water geochemistry is thus important in studying the stalagmite records for interpreting the paleoclimatic change.In this paper,a study was conducted of drip water geochemistry and its response to rainfall by field monitoring at FuRong Cave,Chongqing,China from October 2005 to October 2007.As monitored in two drip sites and two pool sites,there was marked temporal and spatial change in every sites,with the lag time varying with the different features of microfissure porosity in the soil and limestone rock above the drip site.The chemical composition of the soil above the cave also been determined to infer its control on karst hydrogeochemistry.There considerable amount of soluble Ca²⁺and Ma²⁺in soil solution above the cave,which may be leached down to the underlying aquifer by rainwater.Previous studies showed that the variability in drip water Mg/Ca ratio could indicate the water-rock interaction processes.In the dry season,there could exist a durable contact of rock with moisture,probably resulting in an increased Mg/Ca ratio of the solution due to quicker saturation of calcite than calcite precipitation prior to dolomite occurred along the flow path due to degassing of CO₂ from fissure solution,resulting in depletion of Ca²⁺and relative enrichment of Mg²⁺in drip water.However the drip water Mg/Ca ratio in FuRong,Cave showed higher value in summer wet period than in the autumn,winter and spring seasons dry period of the investigation period,which was attributed to by the more favorable leaching of Mg²⁺than Of Ca²⁺form the soil.Variation of speleothem Mg/Ca ratio with cave temperature is insignificant for the temperature in the FuRong Cave is relatively constant within a year,so variation of speleothem Mg/Ca ratio could be indirect indicator of drip water Mg/Ca ratio and,in turn,an indicator of rainfall in warm seasons of the epikarst environmental conditions.However,Precise and accurate interpretation requires more detailed and long term monitoring and calibration of Mg/Ca Ratio variation to climate conditions.