Dynamic characteristics and genesis of strontium-rich groundwater in Xintian county, Hunan Province

In order to understand the dynamic characteristics of Sr-rich groundwater in Xintian county, Hunan Province, two sites were sampled and analyzed regularly for one year（January to December 2017）. The results show that the content of Sr2+ in decline spring S045 remains stable in wet , normal and dry seasons with values of 0.27 mg?kg-1, 0.25 mg?kg-1 and 0.26 mg?kg-1, respectively. The hydrogeological characteristics determine that the dilution effect of rainfall on Sr2+ content in the decline spring S045 is limited, which is the main reason for the relative stability of Sr2+ content in this spring throughout the year. The Sr2+ content in the ZK1 well decreases in wet, normal and dry seasons with values of 0.73 mg?kg-1, 0.68 mg?kg-1 and 0.52 mg?kg-1, respectively. The variation of water level caused by the different water circulation conditions leads to different mixing ratios of high strontium subsurface water and low strontium shallow subsurface water, which is the reason why strontium content in the ZK1 well is positively correlated with atmospheric rainfall. Analysis using the ion ratio method shows that the γ(Na?) /γ(Cl?) in the decline spring S045 is 0.78, 0.44 and 0.49, γ(HCO〖_3^-〗+SO〖_4^(2-)〗) /γ(Ca2++Mg2+) is 0.99, 0.98 and 0.96, γ(Na?) /γ(Cl?) in ZK1 well is 75.24, 71.34 and 126.08, and γ(HCO〖_3^-〗+SO〖_4^(2-)〗) /γ(Ca2++Mg2+) is 37.13, 30.54 and 44.89 in wet, normal and dry seasons, respectively. They indicate that the groundwater experienced cation exchange in the ZK1 well. The average values of the γ(Cl?) /γ(Ca2?) coefficients in the decline spring S045 are 1.09×10-2 in wet season, 1.06×10-2 in normal season and 1.05×10-2 in dry season, respectively. The average values of the γ(Cl?) /γ(Ca2?) coefficients in ZK1 well are 1.29 in wet season, 0.98 in normal season and 0.94 in dry season, respectively. The γ(Cl?) /γ(Ca2?) in the ZK1 well is significantly higher than that in the decline spring S045, indicating that the hydrodynamic condition of the ZK1 well is weaker than that of the decline spring S045, and it is an important factor for the higher Sr2+ content in the ZK1 well than that in the decline spring S045.