Hydrochemical characteristics and geochemical sensitivity of groundwater in typical karst hilly regions:A case study of Eastern Wugang

This study investigated hydrochemical characteristics and geochemical sensitivity of groundwater in a typical karst hilly region. The results indicate that Ca2+ and Mg2+ are the main cations and HCO3- and NO3- are the main anions in the karst groundwater system, which are affected by water-rock interaction and human activities; groundwater system, which is affected by water-rock interaction and human activities. The result also indicates the ratio of Mg2+/ Ca2+, controlled by lithology, is the highest in the dolomite second highest in the limestone dolomite, and the lowest in limestone. In general, the karst groundwater in the study area shows a high geochemical sensitivity which follows the order as HCO3->Ca2+>Mg2+>NO3->SO42->Cl->Na+>K+. In particular,the cation Ca2+ is the most sensitive, followed by Mg2+, while HCO3- is the most sensitive inthe anions, followed by NO3-. The sensitivity level of the karst groundwater in the study area is classified by the most sensitive factor HCO3-. Consequently, the low sensitive water spots account for only 7.27%, the medium sensitive ones account for about 25.45%, while the highly sensitive account for about 67.28%. These statistic results of the geochemical sensitivity division show that the protection of groundwater is very important and urgent.