International Geologiical Congress - Oslo 2008

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HYH-02 Groundwater resources and management

 

Geochemical and stable isotopic evolution of the aquifer system in Qingshuihe basin, northwestern China

 

Xiangquan Li, Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences (China)
Xinwei Hou, Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences (China)
Li Zhang, Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences (China)
 

 

Qingshuihe Basin is located in the southern Ningxia Hui autonomous region (SNHAR), lying on the Loess Plateau of northwestern China, which is the poorest area of the country and extremely short of water resources. Three main characteristics of the water-related environmental conditions in SNHAR can be summarized: (1)SNHAR is in a typical continental arid climatic area,where the water circulation is not active, and surface water is very limited; (2) the complex tectonism of the region has resulted in the geomorphologic feature of mountain alternating with basin ; (3) the qualities of both surface water and shallow groundwater are very poor, and saline water is extensively distributed in the basin; In order to improve the management of the water resources, a hydrogeological study (2000-2005) has been carried out.

In the study, hydrogeochemistry and environmental isotope data were utilized to understand origin, geochemical evolution, hydraulic interconnection, and renewability of groundwater in Qingshuihe Basin, northwestern China. There are four types of groundwater: (1) shallow groundwater in the mountain front pluvial fans, originating from recent recharge by precipitation, (2) deep paleo-groundwater of the lower alluvial plains, which was formed long ago, (3) shallow groundwater in the lower alluvial plains, which has undergone evaporation during the recharge process, and (4) mixed groundwater (shallow and deep groundwater in the plain). The main water types are Na-HCO3, which dominates type (1), and Na-SO4, which dominates types (2) and (3). Geochemical evolution in the upper pluvial fans is mainly the result of CO2 gas dissolution, silicates weathering and cation exchange; in the lower alluvial plains, it is related to mineral dissolution. The evaporative enrichment only produces significant salinity increases in the shallow groundwater of the lower alluvial plains. Shallow groundwater age in the upper plain is 10 years or so, showing a strong renewability. Deep groundwater ages in the lower plain are more than 200 years, showing poor renewability. In the exploitation areas, the renewability of groundwater evidently increases and the circulation period is 70-100 years.

 

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