THE GROUNDWATER RECHARGE AND GEOCHEMICALEVOLUTION FROMHEXI CORRIDOR TOINNER MONGOLIA PLATEAU, THE ARIDZONES OF NOTHWEST CHINA

摘要

The long term recharge in Hexi corridor and Inner Mongolia Plateau was estimated to be 0.96m yr-1 by using the chloridernmass balance method from one unsaturated zone profile, which shows that no effective modern recharge is taking place. Overall therngroundwater quality is good for drinking and irrigation in the Quaternary aquifer of Heihe River and Shiyang river basins. Thernsalinities and the major ions in groundwater increases sharply down stream from the debouchure, more than 1 g l-1 TDS in the lowerrnreaches. The mineralization of groundwater decreases from the shallow aquifer to the deep aquifer. The lakes in the Badain Jaranrndesert are generally of fresh water, although with variable compositions which suggest some in-basin biogeochemical modification.rnStable isotopes (δ18O and δ2H) provide clear distinction between modern and ancient waters. A good rainfall database from nearbyrnZhangye provides definition of the composition of modern rainfall. The signature of groundwater from the late Pleistocene differsrnmarkedly from that of the Holocene, shown clearly by the stable isotopic compositions of -10.5‰ δ18O as compared with values of -rn7‰ at the present day. It is apparent that the groundwaters in the Minqin Basin, Ejina basin and feeding the lake system of thernBadain Jaran are part of a regional flow network related to a wetter past climate as source of recharge. This system is largelyrndecoupled from the river network in this area. The recharge source in the past and to a limited extent in the more arid conditions ofrnthe present day included the foothills of the mountains of the Tibetan plateau.The tritium age determinations accurate to the year arernimpossible and of no meaning to groundwater studies in the region due to tritium measurements in the shallow unconfinedrngroundwater environment could either be influenced by vapor exchange with the soil atmosphere or an expression very localisedrnmodern recharge. A tritium value in the groundwater means multiple recharge ages in this region.