Hydrochemical variations of epikarst springs in vertical climate zones: a case study in Jinfo Mountain National Nature Reserve of China

High temporal resolution (15 min) measurements of stage, pH, electric conductivity, temperature, and other hydrochemical parameters of groundwater at two sites in the Jinfo Mountain Nature Reserve of China were collected using automatic data loggers. Bitan Spring (BS 700 m a.s.l.) sits in subtropical climate zone, while Shuifang Spring (SS 2,060 m a.s.l.) is located in plateau temperate climate. The data show that hydrochemistry of epikarst springs at different altitudes is very sensitive to the changes of their physical environment, especially two factors: air temperature and soil CO₂ concentration. Springs at lower altitude are associated with higher air temperature and soil CO₂ concentration, thus more likely leading to more active karst processes than those at higher elevation. Water temperature and pH of BS showed a noticeable diurnal circle with high values in daytime and low values at night. The data also indicate that at least there are two effects that could impact the variations of groundwater hydrochemistry during flood pulse: dilution effect and CO₂ effect.