Spatial geochemical and isotopic characteristics associated with groundwater flow in the North China Plain

The North China Plain (NCP) is an important agricultural area in China and has a high population density. Serious water shortages have occurred in this region over the last 20 years. Water transfer from the Yangtze River (the east route) was initiated in the year 2002 to provide water for the major cities of the NCP. This study was carried out before the implementation of the water transfer project, focusing on the spatial integration of the groundwater flow system and geochemical characteristics, which are mainly controlled by tectonics, geomorphology, and lithology. The field survey and the geochemical analyses of the groundwater samples indicated that the groundwater in the NCP has a two-layer structure, with a boundary at a depth of about 100-150 in. The two layers differ in pH, concentrations of SiO2, and major ions, and isotopes (O-18, deuterium and tritium (T)). Chemical components in the upper layer showed a wider range and higher variability than those in the lower layer, indicating the impact of human activity. The flow direction of the groundwater in the upper layer was examined in detail in two profiles, showing that the upper layer flows east towards the Canozhou-Daming fault, while the groundwater in the lower layer flows northeast towards Tianjin. Three hydrogeological zones are identified: recharge (Zone 1), intermediate (Zone II), and discharge (Zone 111). The recharge zone was found to be low in chloride (Cl-) but high in T. The discharge zone was found to be high in Cl- and low in T. This may be due to the difference in groundwater age. The discharge zone was subdivided into two sub-zones, Zone II1 and Zone III2 by considering the effects of human activities. Zone III2 was strongly affected by water diversions from the Yellow River. As groundwater flows from the recharge zone to the intermediate and discharge zones, chemical patterns evolve in the order: Ca-HCO3 > Mg-HCO3 > Na-Cl + SO4. Copyright (C) 2004 John Wiley Sons, Ltd.