IDENTIFICATION OF GROUNDWATER RECHARGE SOURCES BY USING EXCESS 234U AND 34S FOR THE ARID EJINA-BADAIN JARAN INTERIOR BASIN OF ALXA PLATEAU, INNER MONGOLIA

摘要

The Ejina-Badain Jaran depression of the Alxa Plateau of Inner Mongolia covers an area of 81,380 km 2with annual mean precipitation of about 50 to 80 mm. It is composed of Gobi, Badain Jaran Shamo (Dune Desert) and two grasslands, Gurinai and Wendu Golei. The intermittent Black River ends into lakes in this depression. Precipitation, surface water and groundwater from dug wells, boreholes and springs were sampled. Big variations of U, 234U ex , 34Ssulphate and 18O, T, 14C of waters were found especially that of U and 234Uex with ranges of 0.06ppb to 1455ppb and –0.408 eU to 13.91 eU respectively. It leads to the differentiation of groundwaters into groups as Gobi, Shamo and the grasslands. The 34 Ssulphate was also used for this purpose due to the sulphate in this huge nomads area is mainly the naturally sourced. The recharge sources of groundwaters were identifi ed by using end members with special reference to the Gurinai grassland. Three source waters of its phreatic groundwater are: the local precipitation, the Gobi groundwater and the leakage from deep aquifers. Three source waters of deep groundwater are: the Gobi groundwater, the deep groundwater from Shamo and, the palaeowater. These recharge sources were checked by other isotopic relationships especially that of 34 Ssulphate . The Gobi water appears the mixing of local precipitation, deep percolation from the Black River and, the deep groundwater from different areas including that from Mongolia. From data of all the sampling sites distributed in Gurinai, an areal averaged contribution of every source water for both the phreatic and deep groundwaters were estimated by using U and 234 Uex .