VARIATION AND EVOLUTION OF GROUNDWATER CHEMISTRY IN PUTIAN PLAIN

The hydrochemical of groundwater in the Holocene, Pleistocene, elurium and bedrock fissures in Putian plain was analyzed. The results show that, hydrochemical types of phreatic water are HCO₃-Ca, HCO₃·Cl-Na·Ca, Cl·HCO₃-Na·Ca, Cl-Na, from the mountain to the sea. There are four features:(1)HCO₃^- and Ca²⁺are remarkable, it is newly formed, with transient material exchange by the surrounding rock minerals, after the subsurface infiltration,(2)Cl^- and Na⁺ are remarkable, it is sealed ancient seawater,(3)Cl^- and Ca²⁺ are remarkable, Na⁺ of the groundwater is exchanged with Ca²⁺ of the minerals in the surrounding rocks,(4)owing to the CO₂ dissolved in water, during the precipitation, the HCO₃^- proportion of the groundwater anion is raised, but the cation composition have stayed the same. Two desalination processes have been found in this article. The first is desalination processes with cation exchange. The second is CO₂ dissolved during leaching.