Effect of precipitation on the hydrochemical variations in Landiantang spring at Nongla, Mashan, China

High-resolution measurements of rainfalls,water level,pH,conductivity and temperature in Landiantang epikarst spring at Nongla,Mashan county in Guangxi Province,China were recorded by using the data logger with time interval of fifteen minutes all the year round. And,the waters from the spring represent the exit for the aquifer's conduit flow. During the rainfalls,it was found that the pH and temperature of Landiantang spring increased and the conductivity reduced. As HCO₃^-, Ca²⁺ and Mg²⁺ were the dominantions,we developed linear relationship between conductivity and those ions. According to the liner relationships,the calcite index(SI_C),the dolomite index(SI_D)and CO₂ partial pressure(LogPCO₂)of the spring were calculated. Results indicated that the LogPCO₂ of spring during rainfalls was lower than that without rain,and its SI_c and SI_D was also lower. By studying epikarst zone,it was known that above result was caused by the dilution of precipitation because rainfall with high pH and low conductivity forming slope stream and traveling through conduit rapidly affected the hydro-chemical variations of epikarst spring.