Geochemistry And ²H And ¹⁸O Stable Isotopes Of Cangzhou Aquifer Systems

Cangzhou is one of the most water-scarce cities in Hebei Plain,where amount per capita of water resources is 192m3, only 8% of the national average level. Therefore, it is of great importance to consider how to reasonably exploit the fresh groundwater and to desalinate the saline groundwater to satisfy water resources management.The dissertation presents a comprehensive study on the evolution of salt solute in shallow groundwater as well as the recharge source of the aquifer system and its stratification in Cangzhou, by employing multidisciplinary methods integrated with historical geography, paleoclimate change and environmental impact analysis based on geochemistry and stable isotope technology.Dynamic water-level, main ions relation, soluble salt chemical equilibrium and saturated indexes of shallow groundwater are analyzed, proving soluble salts experiencing precipitation-dissolution cycles in dry and wet seasonal variation. In dry seasons, water is completely evaporated and all minerals are precipitated. In rainy and irrigation seasons, highly soluble salts have the dissolving priority, excluding those salts having marine origins, and insoluble carbonate minerals tend to become cements, remaining in soil and vadose zones.δ2H (-60~-55‰) andδ18O (-8.4~-7.9‰) values of the shallow groundwater (5~15m of well depth) in Cangzhou are regarded as stable isotope values (δ2H,δ18O) of local modern precipitation by analyzing the distribution ofδ2H andδ18O values and comparing with the weighted average values of precipitation in Shijiangzhuang (IAEA) and records of ice core from Greenland.δ2H (-76~-72‰) andδ18O (-10.7~-10.1‰) values of the deep groundwater (300~450m of well depth) are defined as paleowater in glacial period of Late Pleistocene about 2.5 to 6 million years ago, based on the calculation of 14C data and the comparison of the Camp Century ice core.δ2H (-69~-59‰) andδ18O (-9.6~-8.2‰) values of the other shallow groundwater, sampled at 10~50m of well depth, are below the values of Holocene precipitation recharge, which indicates it is mainly recharged by paleo-Yellow River of Holocene by analyzing local hydrology and historical geography.Therefore, groundwater samples can be divided into 3 groups byδ2H andδ18O values: (1) samples of 5~10m depth recharged by modern precipitation, (2) samples of 10~50m depth mainly recharged by ancient Yellow River, and (3) samples of 300~450m depth considered as paleowater of Late Pleistocene ice age. Main ions and halogen elements are used to show environment of groundwater infiltration to avoid multiple explanations of such isotope method.The integrated application of groundwater dynamics, multi-tracers such as geochemistry and stable isotopes with paleoclimate, historical geography and environmental impact makes up the weak points of an individual method. The results have a theoretical significance of understanding recharge source and salinazation of groundwater, and provide adequate scientific basis for groundwater resources exploitation and saline water desalination.