Environmental isotope study of the groundwater resources in the North Wulan-Buhe desert, Inner Mongolia

The study area of about 4 200 km² includes mainly the north part of the Wulan-Buhe Desert which is situated to the west of the Yellow River in Inner Mongolia,with an annual mean precipitation of 140 mm to 85 mm from its east to southwest.There are 68 sampling sites for groundwaters.In the relation δD=Sδ¹⁸O+d,S=8 and d=10 are get for the precipitation,it is just the same as the WMWL.For the groudwaters,the most δ¹⁸O values lie in the range of -7.4‰ to -12.1‰,the tritium content ranges from 0-190TU while the ¹⁴C values of 1.7-97 pMC are found.In comparison with the precipitation line,six kinds of groundwater with same or different A and d are found.From the isotopic relationships,four recharge sources are identified for the confined groundwater,i.e.,the paleogroundwater,the spring from fissued rocks of Lang Shan mountainous area situated to the northwest of the Desert,the percolation from the Yellow River,and the deep infiltration water from sand dunes which is formed by precipitation with special mechanism.Three source waters of phreatic groundwater are identified,too.They are the recent precipitation,the early episodic precipitation recharge and the water from sand dunes.The contribution of individual recharge source to the confined/phreatic groundwater at different places is estimated by using the mixing model.