No abstract

The groundwater table in the piedmont plain was only about 1-2 m in depth in the 1950s and 1960s, but it lowered dramatically afterwards to about 25-27 m in depth (currently 21-23 m above sea level) due to overpumping of groundwater and drought in the region. This change has adversely affected the sustainable development and food supply of this important agricultural area. The groundwater table at Luancheng Experimental Station of the Chinese Academy of Sciences, located in the piedmont, dropped from 39.36 m in 1975 to 21.47 m above sea level in 1999, at an average rate of 0.72 m/year. Water balance components, such as daily rainfall, pan-evaporation, and evapotranspiration (by lysimeter after 1995) have been recorded since the 1970s, and they were used as variants to simulate monthly water table change based on a physically based statistical model. Groundwater samples were collected during the period 1998-2001, and tritium was measured in the laboratory to trace the groundwater flow from the Taihang Mountains to the piedmont. A reasonable exploitation rate of 150 mm/year was obtained from the model by assuming the annual water table is constant. The recharge and groundwater flow from the Taihang Mountains plays an important role in the water balance of the piedmont area, and it was estimated to be about 112.5 mm/year by using the variation of tritium with the depth, which followed a good exponential function. The simple water balance calculation indicated that the water table could recede at a rate of 0.8 m/year, which is close to the actual situation.

A survey of the quality of groundwater across a broad area of the North China Plain, undertaken in 1998 to 2000, indicates that nitrate pollution is a serious problem affecting the drinking water for a vast population. The use of nitrogen (N)-fertilizer in agriculture has greatly increased over the past 20 years to meet the food needs of the rapidly expanding population. During the study, 295 water samples were collected from wells and springs to determine the water chemistry and the extent of nitrate pollution. High concentrations of nitrate, especially in a recharge area along the western side, but also in the vicinity of Beijing and locally in other parts of the plain, pose a serious problem for the drinking water supply. In places, the nitrate concentration exceeds the maximum for safe drinking water of 45 mg/L. The intense use of N-fertilizer and the widespread use of untreated groundwater for crop irrigation contribute greatly to the problem, but no doubt the disposal of industrial and municipal waste into streams and infiltrating the aquifer also contribute to the problem; however, the lack of data prevents evaluation of those sources. In the recharge area, nitrate is found at depths of as much as 50 m. Near Beijing, relatively high concentrations of nitrate occur at depths of as much as 80 m. In the discharge area, in the vicinity of the Yellow River, high concentrations of nitrate occur at depths of <8 m.ResumØ Une campagne d'Øvaluation de la qualitØ de l'eau souterraine entreprise entre 1998 et 2000 à travers une vaste Øtendue de la plaine du nord en Chine indique que la pollution par les nitrates est un probl me sØrieux qui affecte la qualitØ de l'eau souterraine pour une abondante population. L'utilisation de fertilisants azotØs pour l'agriculture a augmentØ considØrablement durant les 20 derni res annØes afin de rencontrer les besoins alimentaires d'une population à forte croissance. Lors de cette Øtude, 295 Øchantillons d'eau ont ØtØ prØlevØs dans des puits et sources naturelles afin de dØterminer la composition chimique de l'eau souterraine ainsi que l'Øtendue de la pollution par les nitrates. Des concentrations ØlevØes de nitrates, en particulier dans une zone de recharge le long de la limite ouest de la plaine, mais aussi dans la rØgion de Beijing et sporadiquement dans la plaine, posent de sØrieux probl mes à la consommation de l'eau souterraine. A certains endroits, la concentration en nitrates exc de la valeur maximale acceptØe pour la consommation qui est de 45 mg NO 3 /L. L'utilisation intensive de fertilisants azotØs ainsi que l'utilisation rØ-pandue d'eau souterraine non traitØe pour l'irrigation contribuent pour beaucoup au probl me, mais il ne fait pas de doute que le rejet des dØchets municipaux et industriels dans les rivi res et aquif res y est aussi pour quelque chose. Par contre, le manque de donnØs ne permet pas d'Øvaluer la contribution de chacune de ces sources. Dans la zone de recharge, les nitrates se retrouvent à des profondeurs allant jusqu'à 50 m. Pr s de Beijing, ...

No abstract

Rapid groundwater drawdown in Gaocheng City, the alluvial plain of the Taihang Mountain in the North China Plain, has become the biggest threat to agricultural sustainability. In order to determine the factors resulting in the groundwater decline and to develop a practical plan for long-term groundwater use, water-table fluctuation data were collected over a period of 25 years. The analysis showed that although the drawdown of the water-table was mainly due to water used for winter wheat production and other crops, another reason for groundwater level decline was the tremendous decline of upstream groundwater recharge. It was estimated that, compared to the 1970s, decrease in upstream groundwater recharge in the 1990s resulted in about 1.2 m/a of groundwater level decline. Thus, decline of upstream groundwater recharge rather than agricultural water use was the main reason for the recent groundwater drawdown. On the other hand, gradually improved agricultural practices have saved a great deal of water since the 1970s. The analysis also revealed that, although the groundwater level declined during the wheat-growing season, corn-growing season and over the whole year strongly correlated with the amount of precipitation in that period, aside from one year of extremely high precipitation, precipitation did not recharge groundwater directly but affected groundwater levels through a decrease in irrigation water use. Finally, in order to maintain the groundwater balance, agricultural practices have to save about 180 mm/a of irrigation water from their present level.

Abstract: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 m. The two layers differ in pH, concentrations of SiO 2 and major ions, and isotopes ( 18 O, 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 Cangzhou-Daming fault, while the groundwater in the lower layer flows northeast towards Tianjin. Three hydrogeological zones are identified: recharge (Zone I), intermediate (Zone II), and discharge (Zone III). 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 III 1 and Zone III 2 , by considering the effects of human activities. Zone III 2 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-HCO 3 > Mg-HCO 3 > Na-Cl C SO 4 .

Abstract:In arid and semi-arid regions there is usually a shortage of irrigation water; thus, wastewater water, as well as other lowquality water resources, may become an important source of water and nutrients. However, (pre)treated wastewater may contain elements and compounds that can damage the environment. It also has the potential to affect water quality adversely in an aquifer that may be the source of drinking water in the area. In order to assess the impacts of wastewater on the environment, groundwater samples were taken and analysed in typical croplands in the North China Plain, where urban wastewater or groundwater have been used for irrigation for several decades. Concentrations of nitrate NO 3 in groundwater in the study area varied from 50 to 130 mg l 1 in the croplands irrigated by wastewater, but in the croplands irrigated by pumping wells, away from the Dongming Canal, NO 3 concentrations are less than 35 mg l 1 . It was found that values of υ 15 N ranged from C5 to C13‰, and dominantly from C7 to C11‰, and the NO 3 concentration in most wells with depths of less than 40 m was higher than the drinking water standard set by the WHO. Cluster analysis was used to classify the spatial distribution of nitrates resulting from the wastewater. Identification of chemical patterns is found to be effective for the comprehensive assessment of the spatial distribution of groundwater quality. It is also emphasized that the wastewater in this area controls the NO 3 distribution in the groundwater, and should be used carefully to protect both soil and groundwater from NO 3 pollution.

Abstract:To identify the groundwater flow system in the North China Plain, the chemical and stable isotopes of the groundwater and surface water were analysed along the Chaobai River and Yongding River basin. According to the field survey, the study area in the North China Plain was classified hydrogeologically into three parts: mountain, piedmont alluvial fan and lowland areas.The change of electrical conductance and pH values coincided with groundwater flow from mountain to lowland areas. The following groundwater types are recognized: Ca-HCO 3 and Ca-Mg-HCO 3 in mountain areas, Ca-Mg-HCO 3 and Na-K-HCO 3 in piedmont alluvial fan areas, and HCO 3 -Na in lowland areas.The stable isotope distribution of groundwater in the study area also has a good corresponding relation with other chemical characteristics. Stable isotope signatures reveal a major recharge from precipitation and surface water in the mountain areas. Chemical and stable isotope analysis data suggest that mountain and piedmont alluvial fan areas were the major recharge zones and the lowland areas belong to the main discharge zone. Precipitation and surface water were the major sources for groundwater in the North China Plain. Stable isotopic enrichment of groundwater near the dam area in front of the piedmont alluvial fan areas shows that the dam water infiltrated to the ground after evaporation.As a result, from the stable isotope analysis, isotope value of groundwater tends to deplete from sea level (horizontal ground surface) to both top of the mountain and the bottom of the lowland areas in symmetrically. This suggests that groundwater in the study area is controlled by the altitude effect. Shallow groundwater in the study area belongs to the local flow system and deep groundwater part of the regional flow system.