Variations of Ca2+、Mg2+、Sr2+ in groundwater and surface water from the Xueyu cave

A one year study of water geochemistry was performed in the Xueyu cave in 2011, the concentrations of Ca2+、Mg2+、Sr2+ and elemental ratios of Mg/Ca、Sr/Ca in drip water, groundwater and epikarst spring water from the overlaying bedrock as well as the surface water from the Long River were measured. The results indicate the variation of Ca2+、Mg2+、Sr2+ along with the precipitation was notable. The Ca2+ in epikarst spring water can response with the change of precipitation sensitively. The drop water responses to the change of precipitation may last for a month. The rainy season and the dry season can be reflected by the underground water. The content of Ca2+in the surface water was stable all year round but had pronounced reflection to extreme dry weather. The variations of Mg2+ and Sr2+ in different types of water were consistent with each other yearly in 2011, and the concentrations of Mg2+ and Sr2+ were lower in March, May and October with much rainfall, but higher in other months with little rainfall. The above changes in cation concentrations were related to the dilution effect, CO2 effect and lithology. The ratios of Mg/Ca and Sr/Ca in different kinds of waters from the Xueyu cave system ranged from high to low as follows: drip water, surface water, ground water and spring water, reflecting different detention time in the aquifer media and reacting time with bedrock. The ratios of Mg/Ca and Sr/Ca were low during wet period and high during dry period. For the impact of the former calcium carbonate precipitation and the variance in transport routes, there are slight differences in the ratios of Mg/Ca、Sr/Ca. Therefore, the change of ions concentration and their ratios in different types of water is different in the responding time and features to external precipitation, which deciding that it should make difference when determining external environmental changes with the elements and their ratios.