Characteristics of Chemistry and Stable Isotopes in Groundwater of Chaobai and Yongding River Basin, North China Plain

HYDROLOGICAL PROCESSES Hydrol. Process. 22, 63–72 (2008) Published online 17 September 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6640

Characteristics of chemistry and stable isotopes in groundwater of Chaobai and Yongding River basin, North China Plain

K. Aji,1* C. Tang,2 X. Song,3 A. Kondoh,4 Y. Sakura,5 J. Yu3 and S. Kaneko1 1 Graduate School of Science and Technology, Chiba University, 1-33 Yayoi, Inage-Ku, Chiba 263-8522, Japan 2 Department of Environmental Science & Landscape Architecture, Faculty of Horticulture, Chiba University, Japan 3 Institute of Geographical Sciences & Natural Resources Research, CAS, Beijing, People’s Republic of China 4 Center for Environmental Remote Sensing, Chiba University, Chiba 263-8522, Japan 5 Department of Earth Sciences, Faculty of Science, Chiba University, Chiba 263-8522, Japan

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–HCO3 and Ca–Mg–HCO3 in mountain areas, Ca–Mg–HCO3 and Na–K–HCO3 in piedmont alluvial fan areas, and HCO3 –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. Copyright  2007 John Wiley & Sons, Ltd.

KEY WORDS groundwater; chemical characteristics; stable isotopes; North China Plain Received 16 November 2004; Accepted 1 November 2006

INTRODUCTION The North China Plain is a thick Cenozoic sedimen- 2 The North China Plain is China’s leading industrial and tary basin covering approximately 150 000 km and is agricultural area, but it suffers from the systematic prob- bordered by the Yanshan Fold to the north, the Taihang lems of water shortage related to rapid urbanization, swell to the west, the Yellow River in the south and the industrialization, growing agricultural demand and envi- Bohai Sea in the east (Chen et al., 2003). For the North ronmental degradation. These developments have been China Plain, generally groundwater recharge occurs in heavily dependent upon groundwater resources. In past the Taihang and Yanshan Mountains, and the ground- decades the aquifers in the North China Plain have been water in the North China Plain flows the southeastward rapidly developed for urban and industrial water supply and southward to the Bohai Sea (Shi et al., 1998; Zhang and for agricultural irrigation. Groundwater in the North et al., 2000). Most recharge is from infiltration of pre- China Plain is used at a rate much higher than that with cipitation near the outcrop area of the piedmont alluvial which the aquifers are filled. This has caused the level fan and the mountain areas, but a small percentage is of groundwater to drop, in some places by as much as from interring-aquifer leakage in the eastern part of the 70 m. In Beijing, the drop has been 40 m and the city plain (Shi et al., 1998; Zhang et al., 2000). Hydraulically has subsided by over 0Ð5 m (Olli and Pertti, 2001). As continuous flow systems occur through the Quaternary a result, the water table beneath the North China Plain aquifers in the North China Plain (Shi et al., 1998; Zhang has an average declined at a rate of 1–1Ð5 m year1 et al., 2000). (Wang et al., 2005). In the North China Plain, the groundwater in recharge areas is distinctive in its low concentration of NaC but high concentrations of Ca2C and Mg2C and is classified as * Correspondence to: K. Aji, Graduate School of Science and Technol- ogy, Chiba University, 1-33 Yayoi, Inage-Ku, Chiba 263-8522, Japan. Ca–Mg–HCO3 type. In contrast, elsewhere the ground- C E-mail: [email protected], [email protected] waters are high in NaC and low in Ca2 and Mg2C; either

Copyright  2007 John Wiley & Sons, Ltd. 64 K. AJI ET AL. of type Ca–Mg–HCO3 or Ca–Mg–Cl are found (Chen HYDROGEOLOGICAL SETTINGS OF STUDY et al., 2001). AREA Groundwater in the deep aquifer of the North China Plain derived a palaeoclimate record from stable iso- The study area is located at the north part of the North 14 et al China Plain, and includes Beijing, Tianjin, and Hebei tope ratios and has been dated by C(Chen ., ° 0 ° 0 ° 0 ° 0 2003). The υDandυ18O values in the deep aquifer province (115 00 E–118 00 E and 39 00 N–41 00 N) beneath the North China Plain reflect differences in (Figure 1). It belongs to the littoral and semiarid climatic zone and has an annual temperature of 12–13 °C. The palaeoclimate between the Holocene and the late Pleis- mean annual precipitation ranges from 400 to 600 mm. tocene. The 14C ages of groundwater are between 12 000 The precipitation is dominated by the Asia summer and 25 000 years BP have ranged from 76 to 85‰ monsoon during July to September that accounts for for υDand9Ð4to11Ð7‰ for υ18O values (Chen about 70% of annual precipitation (Zhang et al., 2000). et al., 2003). The depleted stable isotope values of deep There is only 40 to 60 mm of rainfall occurs over more groundwaters observed in lowland areas near Tianjin than 100 days in spring. Mean potential evaporation (Duan et al., 2004) show that there was a pluvial-period ranges from 1100 to 1800 mm (Liu and Wang, 1992). groundwater recharged 15 000–20 000 year BP during a The regional Quaternary aquifers in the North China cold climate regime. Such studies also confirm the find- Plain consist of fluvial fans, alluvial fans and lacustrine ings of Foster et al. (2004), which show the value deposits (Zhang et al., 2000; Chen et al., 2003). Quartz, of chemical and isotopic characteristics in identifying potassium feldspar and hornblende are the dominant min- recharge and discharge areas and also the existence erals in the deep aquifers. Calcite is commonly present. of palaeo-recharged groundwaters in the North China Illite, kaolinite and montmorillonite may also be observed Plain. (Chen and Ni, 1987). These sediment deposits of the Qua- The purpose of this paper is to explain the chemical and ternary layer are classified into four aquifers based on the stable isotope characteristics of groundwater flow from lithologic properties and hydrodynamic conditions. The Yanshan Mountains to the Bohai Sea, where study has sedimentary rocks range in age from Archaean to Qua- previously been limited. Attention has been focused on ternary. The bedrock is composed of Archaeozoic gneiss the spatial distributions of the chemical and isotopic con- and Proterozic carbonate (Chen et al., 2003). The Ceno- tent of groundwater flow in the Basin of Chaobai and zoic formation consists of thick Tertiary and Quaternary Yongding River. Further, the characteristics of ground- deposits. The genetic type of Quaternary deposits is com- water movement in the mountain, piedmont alluvial fan plex and their thickness varies considerably from 150 to and lowland areas have been discussed separately. There 600 m (Chen et al., 2003). In front of the mountains, is no significant bounding between alluvial fan and low- the Quaternary sequences consist of alluvial, pluvial sed- land areas. iments. In the middle of plain they are mostly layers of

Figure 1. Map of study area and sampling locations

Copyright  2007 John Wiley & Sons, Ltd. Hydrol. Process. 22, 63–72 (2008) DOI: 10.1002/hyp CHEMISTRY AND STABLE ISOTOPES IN GROUNDWATER OF NORTH CHINA PLAIN 65 alluvial and lacustrine sediments, and the main part near RESULTS AND DISCUSSION the coastal plain contains several marine deposit layers. Based on hydrogeological settings, chemical analyses Quaternary deposits chiefly consist of monotonous loess- and stable isotopic characteristics we can classify the like sediments interbedded with sand or gravel. groundwater samples into two types: shallow and deep. Shallow groundwater is the depth above 100 m and deep groundwater is the depth below 100 m. The bounding METHODS place at about 100–150 m depth between these two types was a confined layer. Infiltration and evaporation control Water samples were collected in September 2003 for the quality of groundwater up to the depth of the confined stable isotope and major ions analyses. Forty-six samples layer. were collected from groundwater, two samples collected from the Guanting Dam near Beijing and three samples Hydrochemistry from the river in the mountain area. The samples from the dam were collected in different areas: one in the Chemical and isotopic measurements complement upper part located in the mountain area and the other hydrogeologic observations by providing direct evidence in the lower part was located in the piedmont alluvial for groundwater sources and transport rates. This has fan area. Additionally, three precipitation samples were been demonstrated for many simple groundwater flow taken: one was collected in the piedmont alluvial fan area systems (Davisson et al., 1999). Some chemical charac- and the other two in the mountain area. The groundwater teristics of samples of the study area are shown in Table I. samples were taken from pumping wells with different Precipitation samples do not have chemical records. depths at the same site, in order to get vertical variations of potential heads and chemical futures of groundwater. Characteristics of pH and EC Temperature, electrical conductance (EC) and pH were In mountain areas, pH values of groundwater ranged measured in situ. Water samples were analysed in the from 7Ð32 to 8Ð03 (Figure 2). The variation of the laboratory of Chiba University. The anions and cations pH value of groundwater decreased following elevation were measured by ion chromatography (Shimadzu LC- from the top of the mountain to sea level. The EC 10A), and bicarbonate ion was measured by titration (pH values of groundwater ranged from 290 to 1027 µScm1 4Ð8 alkalinity). υDandυ18O were measured by mass (Figure 3). The EC values showed high values in shallow spectrometer (Finnigan Mat Delta S Thermoqest). groundwater. The EC values of groundwater tend to

Table I. The chemical results of the water samples in study area

a a Station Well pH EC NO3 Place Station Well pH EC NO3 Place depth (m) (µScm1) (mg l1) depth (m) (µScm1) (mg l1)

G1 7 7Ð32 519 48Ð5 Mountain G28 30 7Ð19 1511 60Ð9 Piedmont G2 6 7Ð49 580 33Ð9 Mountain G29 160 8Ð11 680 0 Piedmont G3 25 7Ð66 1010 84Ð2 Mountain G30 16 7Ð17 1302 90Ð4 Piedmont G4 38 7Ð79 737 19 Mountain G31 160 8Ð02 396 0 Piedmont G5 80 7Ð68 500 16Ð8 Mountain G32 120 7Ð9 587 0 Piedmont G6 120 7Ð86 290 4Ð4 Mountain G33 60 7Ð44 1135 0 Piedmont G7 60 7Ð92 389 5Ð6 Mountain G34 55 7Ð27 1215 0 Piedmont G8 30 7Ð58 1027 181 Mountain G35 75 7Ð63 976 0 Lowland G9 100 7Ð89 378 4Ð8 Mountain G36 27 7Ð02 1623 0 Lowland G10 70 8Ð03 563 22Ð3 Mountain G37 300 8Ð17 734 0 Lowland G11 65 7Ð67 559 35Ð1 Mountain G38 70 7Ð22 2220 0 Lowland G12 32 7Ð51 552 17Ð3 Mountain G39 300 8Ð62 886 0 Lowland G13 60 7Ð71 751 46Ð3 Mountain G40 37 8Ð84 815 0 Lowland G14 100 7Ð69 869 0 Mountain G41 200 8Ð08 399 0 Lowland G15 40 7Ð06 2050 148Ð8 Piedmont G42 25 7 944 0 Lowland G16 53 7Ð48 1366 62 Piedmont G43 36 6Ð86 10770 0 Lowland G17 65 7Ð54 1526 58Ð7 Piedmont G44 400 8Ð55 624 0 Lowland G18 45 7Ð46 1182 16Ð3 Piedmont G45 240 8Ð22 823 0 Lowland G19 170 7Ð88 513 0 Piedmont G46 260 8Ð32 748 0 Lowland G20 114 7Ð73 545 0 Piedmont D1 8Ð97 721 0 Mountain G21 80 7Ð65 536 11Ð7 Piedmont D2 8Ð83 726 0 Piedmont G22 40 6Ð82 335 18Ð3 Piedmont R1 8Ð13 1296 10Ð1 Mountain G23 30 7Ð12 1215 245 Piedmont R2 7Ð33 416 Mountain G24 30 7Ð31 110 0 Piedmont R3 7Ð26 310 Mountain G25 80 7Ð56 981 0 Piedmont P1 Piedmont G26 240 7Ð44 554 0 Piedmont P2 Mountain G27 150 7Ð74 1008 0 Piedmont P3 Mountain a G represents groundwater, D dam water, R river water and P precipitation.

Figure 2. Variation of pH values of groundwater and surface water at different elevations

Figure 3. Variation of EC values of groundwater and surface water at different elevations increase with decreasing elevation. The pH values of river 399 to 10 770 µScm1 (Figure 3). The maximum value water ranged from 7Ð26 to 8Ð13 and the EC values ranged occurred in the shallow groundwater near Tianjin City 1 from 310 to 1296 µScm . The pH and EC values of with low pH (the maximum EC value is not plotted in river water in the upper part of the mountain were similar the diagram). The vertical tendencies of the pH and the to the values of adjacent groundwater. The maximum EC EC values in groundwater were the same as for piedmont value of river water was observed in the mountain areas alluvial fan area and similar to the mountain area with close to Guanting Dam at point R1 (Figure 1). The pH regard to the symmetric line. value of dam water was close to 9 and the EC value was The pH and EC values suggest that the altitude effect 721 µScm1 at point D1 (Figure 1). is one factor that changes the water quality in the In the piedmont alluvial fan area, pH values of study area. When the altitude is close to ground surface groundwater ranged from 6Ð82 to 8Ð11 and EC values or sea level from both top and bottom, groundwater ranged from 396 to 2050 µScm1.HighECvalues is subject to both natural and anthropologic effects were observed in shallow groundwater around Beijing (Kleczkowski, 1963). The variations of the pH and EC City. The maximum value reached 2050 µScm1 in values vary symmetrically from sea level both to the top shallow groundwater with a low pH value at point G15 of the mountain and the bottom of the lowland areas (Figure 1). The pH of groundwater tends to increase with in the vertical direction. The pH values tend to increase decreasing elevation, but the EC value tends to decrease symmetrically from sea level to the mountain top and with decreasing elevation. Near the west part of Beijing the bottom of lowland areas along the elevation. The some increased EC and pH values were observed, which EC value tends to decrease symmetrically from sea level were probably the result of human activity. The pH and in the two opposite directions vertically. The tendency EC values of the dam water were 8Ð83 and 726 µScm1 of pH and EC values in groundwater has a symmetric respectively at point D2 (Figure 1). The pH and EC variation in opposite vertical directions. This suggests values of the dam water were similar to the other dam that deep groundwater in lowland areas and mountain water values in the mountain area. shallow groundwater in the study area is ﬂowing under In lowland areas, the pH values of groundwater ranged a symmetric relationship in chemical process of pH and from 6Ð86 to 8Ð84 and the EC values ranged from EC with opposite direction from sea level.

Copyright  2007 John Wiley & Sons, Ltd. Hydrol. Process. 22, 63–72 (2008) DOI: 10.1002/hyp CHEMISTRY AND STABLE ISOTOPES IN GROUNDWATER OF NORTH CHINA PLAIN 67

Figure 4. Trilinear diagram of groundwater and surface water samples in the study area

Chemical patterns of groundwater samples NC occurred in even equal amounts to half In mountain areas, groundwater was characterized of HCO3 . The groundwater types were recognized as 2C HCO3 –Na. as dominantly Ca and HCO3 and with a relatively increased content of Mg2C, as the recharge zone con- In the study area, the chemical pattern of the ground- centration of NaC of groundwater was relatively low and water evolves in the order Ca–Mg–HCO3 > Na–K– HCO > HCO –Na as groundwater flows from the was readily classified as Ca–(Mg)–HCO3 type, as shown 3 3 in the Piper diagram (Figure 4). This is the same water mountain to lowland areas. Dam water and river water type as Taihang Mountain in the North China Plain stud- plotted as a non-dominant type in the diagram. ied by Chen et al. (2001) and corresponds to the normal In the vertical direction, chemical properties of deep pattern given by Toth (1999). groundwater in the study area were generally much the In piedmont alluvial fan areas, the chemical compo- same due to the long residence time. With growing 2 sition of the groundwater varied widely. Most of the distance from the mountains, SO4 and Cl gradually 2C increased. But the ionic ratio did not suggest any influ- groundwater was Ca and HCO3 dominated, the occurrence of NaC was rather rare and there were increases ence of the sea upon the salinity of the groundwater later of Mg2C in the intermediate mountain hill. The within the plain. Deep groundwater was mainly ultra- groundwater type near the mountain hill was generally fresh or fresh of the Ca–Mg–HCO3 –(Na) type. The C the same as the mountain area. In the incorporated dis- occurrence of the Na is rather rare. This suggests that charge area, groundwater had a high NaC concentration the chemical characteristics of deep groundwater are and low Ca2C and Mg2C concentrations. With grow- controlled by the underground circulation (Kleczkowski, 2 ing distance from the mountain hill, the SO4 and Cl 1963). The chemical properties of shallow groundwater gradually increased; the maximum values occurred near mainly tend to strongly mineralized, and the ground- Beijing. However, HCO3 remains the prevailing anion; water ranged from fresh to brackish from the moun- groundwater was observed to be Na–K–HCO3 type. tain toward the coastal plain of lowland areas. Shal- In lowland areas, groundwater quality was diverse, low groundwater was semi-fresh and semi-brackish water 2C being mainly dominated by a low concentration of Mg of Na–Mg–HCO3 –SO4 type and Na–Mg–HCO3 –Cl and a high concentration of NaC and later by a gradual in the piedmont alluvial fan areas. The saltiest water increase in the Cl. A gradual percentage decrease of (3077 mg l1 in Cl) was identified in the coastal area Ca2C and increase of NaC are found in groundwater, near Tianjin at point G43 (Figure 1). In the upper part indicate the extent to ion exchange reactions have taken of the deep layer, which bounds with the shallow layer, place along the flow path, which in tern drive calcite the groundwater was observed to be fresh and semi- into dissolution. At a long distance from the mountain, brackish mixed water. The chemical properties of shallow NaC predominated over the remaining cations; in some groundwater were developed under a strong influence

Copyright  2007 John Wiley & Sons, Ltd. Hydrol. Process. 22, 63–72 (2008) DOI: 10.1002/hyp 68 K. AJI ET AL. of geographic factors, such as climate, morphology and are primarily controlled by differences in latitude and alti- anthropology (Kleczkowski, 1963). tude (Epstein and Mayeda, 1953; Craig, 1961; Dansgaard, The NO3 content was low in river and dam water. 1964). For example, partial evaporation of raindrops dur- NO3 was detected in shallow groundwater in the moun- ing rainfall is particularly noticeable for light rains in arid tain and piedmont alluvial fan areas. In lowland areas, and semiarid zones (Friedman et al., 1962; Gat, 1971; groundwater was mainly pumped up from the deep layer Stewart, 1975; Allison et al., 1984). Evaporation of sur- (Foster et al., 2004). The NO3 value of water samples face runoff and shallow groundwater can also occur (Gat with well depth is shown in Table I. In shallow ground- and Dansgard, 1972; Allison et al., 1984). This has been 1 water, the maximum value of NO3 (84Ð2mgl )was documented in some detail for the North China Plain identified at point G3 (Figure 1) with 25 m depth of well, (Chen et al., 2003). In the study area, 70–80% of annual and the minimum value (4Ð8mgl1) was identified at rainfall derives from summer precipitation; this is the pri- point G9 (Figure 1) with 90 m depth of well in the moun- mary factor for enrichment of the stable isotopes during tain area. In the piedmont alluvial fan area, the maximum the mass migration of storms. value (148Ð8mgl1) was identified near the western part of Beijing at point G15 (Figure 1). with 40 m depth of Stable isotopes in mountain areas well and the minimum value (16Ð3mgl1) was identified In mountain areas, stable isotope values of modern at point G18 (Figure 1) in shallow groundwater. precipitation show a 0Ð88‰variation between 150 and Irrigation and nitrogenous fertilizer application in 780 m and tends to decrease with increasing altitude, excess of crop requirements tend to increase the poten- which is consistent with well-known altitude effects 18 tial risk of NO3 pollution to groundwater (Martin et al., (Dansgaard, 1964; Smith et al., 1979). The υ Ovalues 1994). In mountain areas, NO3 is present in all sam- of precipitation were lighter than 9Ð0‰ at high altitude ples, and some were even higher than piedmont alluvial and heavier than 8Ð5‰ in low altitude areas. These fan. Considering the land use in this area, excessive values were preserved in shallow groundwater and river application of nitrogenous fertilizer in agriculture con- water at the same place. This suggests that precipitation tributed NO3 to groundwater (Anning et al., 2005; Kelin is one of the major sources of water to recharge in the et al., 2005). The increase in EC value of river water at mountain areas. point R1 (Figure 1) is probably the result of the human Stable isotope values of river water also exhibited an activity mentioned above. In piedmont alluvial fan areas, altitude effect as precipitation besides the lower part in the mountain areas. The υ18 Ð NO3 concentration in shallow groundwater was very O values ranged from 7 0 to 9Ð1‰. It seems that the river water recharged a high. NO3 was found in the groundwater at a depth of 70–80 m near Beijing with high EC values. The urban different source of water type at different latitudes. In area of Beijing has advanced dramatically in recent years, some places, stable isotopes in river water were similar and a lot of land in the suburbs that was cropped to cere- to the precipitation, and in some places similar to the als is now used for vegetable production, which requires groundwater at the same altitude. In the eastern part of much more water and chemical pesticides. The other way mountain areas the isotope values of river water coincided with latitude and altitude effects, but were not in the in which groundwater NO3 pollution mainly occurred in County seat areas is due to wastewater irrigation from western part. The υ18O values of river water at point agricultural fields in the North China Plain (Kelin et al., R1 in the western part were more enriched than at point 2005). This suggests that infiltration of surface water and R3 (Figure 1) in the eastern part. Both samples were irrigation water also displays an important role in the located at the same elevation, but different latitudes. quality of shallow groundwater, because mountain areas Probably, latitude could be the main factor controlling and suburban areas in piedmont alluvial fan areas are the evaporation of surface water during runoff (Gat and also major recharge areas for groundwater, as mentioned Dansgard, 1972). 18 above. In some samples of deep groundwater from the The υ O contour map of the study area is shown in southern part of Beijing, which is the boundary between Figure 5. It shows 2Ð9‰variation between 0 and 515 m above sea level, and the value tends to decrease with the piedmont and lowland areas, NO3 was not detected. increasing altitude. The variation of stable isotope content The NO3 properties of shallow groundwater possibly demonstrate the relationship of local shallow groundwater of groundwater had a good correlation with river water circulation in mountain and piedmont alluvial fan areas. and precipitation. It was similar to the values of river water and precipitation at the same altitude. Probably, this was a result of the surface water–groundwater interaction Stable isotopes and direct infiltration by modern precipitation. These phe- Stable υDandυ18O isotopes are ideal tracers for esti- nomena were confirmed in the mountain area of the North mating the recharge areas and flow path of groundwater, China Plain (Aji et al., 2006). This suggests that the because they make up the water molecules and are sensi- groundwater, surface water and precipitation have a good tive to physical processes such as mixing and evaporation connection in mountain areas. At first, groundwater and (Coplen, 1993). The temperature of water evaporation surface water are recharged by precipitation; interchanges and condensation governs the variation of υDandυ18O then occurred between them under the special geological values in natural waters, such that geographic variations and morphological regimes (Kleczkowski, 1963).

Copyright  2007 John Wiley & Sons, Ltd. Hydrol. Process. 22, 63–72 (2008) DOI: 10.1002/hyp CHEMISTRY AND STABLE ISOTOPES IN GROUNDWATER OF NORTH CHINA PLAIN 69

Figure 5. Plot of υ18O in different water tables from sea level of groundwater, precipitation and surface water

The similarity of the stable isotope content of precipi- The stable isotope value of υ18O in dam water at point tation at point P3 and river water at point R3 (Figure 1) D1 (Figure 1) from mountain areas was 3Ð76‰ due to could demonstrate the suggestion of river water recharged the evaporation. This suggests that surface water exists by precipitation in the high mountain. Stable isotope con- under an evaporation effect. tents in precipitation P1 and P2 were similar to groundwater at points G2, G3, G4, G8, G10, and G11 (Figure 1) at Stable isotopes in piedmont alluvial fan areas the same elevation and latitude, implying that groundwa- In the piedmont alluvial fan areas, stable isotope ter in mountain areas also recharged from precipitation. values of groundwater depleted from mountain hill to This suggests to us that groundwater and surface water lowland area, but there is significant difference in shallow in mountain areas is recharged by precipitation. The sta- and deep groundwater. Stable isotope values of shallow ble isotope values were depleted in the groundwater in groundwater ranged from 7Ð39 to 8Ð82‰ in υ18O the upper part of the Guanting Dam, such as at points and it tends to enrich near the ground surface. Those G5, G6, G7 and G9 (Figure 1). Stable isotope values values were similar to precipitation at point P1, P2 of groundwater in this part show an apparent reversal and river water at point R1, R2 (Figure 1). It suggests of the latitude effect. These values were very different that shallow groundwater in this part recharged by the to precipitation and river water in adjacent places, but local precipitation and surface water. It suggests shallow similar to precipitation at point P3 (Figure 1) at high alti- groundwater samples in this area were part of local tude. Probably, groundwater moving upward from the groundwater flow system. deep layer causes isotopic depletion of the imperme- Stable isotope values of deep groundwater were very able layer of the dam structure (Aji et al., 2006). Stable depleted in piedmont alluvial fan areas, with the υ18O isotope values of groundwater and river water were values ranging from 8Ð09 to 11Ð12‰. Groundwater enriched in the mountain hill area, such as points G1, had a lower υ18O and likely was transported from higher G12, G13, R1 and R2 (Figure 1). Probably, groundwa- latitudes and altitudes. Chen et al. (2003) observed a ter was recharged by the river water, causing surface- similar result for a groundwater study in the North China water–groundwater interaction. In this part, maybe sur- Plain. Probably, deep groundwater samples correspond to face water plays a major role in enrichment of ground- the regional groundwater flow system. water isotopes. The groundwater in mountain areas was Around Beijing City the stable isotope values of recharged by the direct diffuse recharge of precipitation, shallow groundwater were enriched and ranged from as well as by recharge from the river water. The iso- 3Ð86 to 5Ð47‰ in υ18O. These values are very similar tope composition of precipitation and river water was to the values in dam water collected from both mountain probably reflected in the shallow groundwater. Such a and piedmont alluvial fan areas. Those samples were result was observed in Taihang Mountain in the North located in the western urban area of Beijing and the lower China Plain (Chen et al., 2003). We can conclude that the part of the dam. The υ18O values of both dam waters at mountain region in the North China Plain is a recharge points D1 and D2 were very close to the isotope values zone for the local and regional groundwater flow sys- of groundwater at points G15, G16 and G17 (Figure 1) tem. near the hill of Yanshan Mountain. This indicates that

Figure 6. Plot of υDandυ18O of various water samples in the study area groundwater has a correlation with dam water as a result groundwater in high-elevation mountain areas and low- of the dam-water–groundwater interaction or mixing, as elevation deep groundwater. This result suggests to us shown in Figure 6. the existence of a correlation between deep groundwater in lowland areas and mountain areas. The maximum Stable isotopes in lowland areas values were found near Beijing in piedmont alluvial fan areas, which are located close to ground surface. In this In lowland areas, stable isotope values of groundwater area, groundwater isotope very same with surface water depleted with decreasing altitude from sea level. Stable at the same altitude. Geographic and geomorphologic isotope values of deep groundwater ranged from 9Ð52 18 effects cause isotopic enrichment of groundwater near the to 10Ð41‰ in υ O. When the groundwater reached the surface (Kleczkowski, 1963). In the North China Plain, deep layer, the stable isotope values were more depleted. when groundwater flows in the mountain areas, the stable These low values indicate that deep groundwater samples isotope is depleted due to local recharge. When ground- represent part of a regional groundwater flow system water arrives in piedmont alluvial fan areas, the stable (Chen et al., 2003). As a regional groundwater flow isotope is enriched in the shallow layer due to geographic system in the North China Plain, deep groundwater and geomorphologic effects. When groundwater reaches has a good isotopic correlation to deep groundwater lowland areas, the stable isotope is depleted again in in piedmont alluvial fan areas. A previous study also the deep layers as a result of the recharge under the confirmed that the stable isotope values were depleted cool palaeoenvironment (Chen et al., 2003). On the other in this area and indicated the values to be pluvial-period groundwater recharged during a cold climate regime hand, groundwater is recharged by precipitation and sur- and passed 100 km before it discharges (Duan et al., face water in mountains areas and flows to lowland areas 2004). Stable isotope values of shallow groundwater via the piedmont alluvial fan areas. During these pro- quite enriched compared with deep groundwater and cesses, groundwater flow separates in to two flows in the ranged from 7Ð37 to 8Ð45‰ in υ18O. These stable mountain hill and the piedmont alluvial fan. One is a isotope values were very similar to the values of shallow local shallow groundwater flow system in the mountain groundwater in piedmont alluvial fan areas. Probably, it hill and piedmont alluvial fan areas, and other is a deep was flowing from piedmont alluvial fan areas as a part regional groundwater flow system. Groundwater coming of the local shallow groundwater flow system. from the mountain to lowland areas flowing through the The stable υ18O value of groundwater tends to deplete deep layer in piedmont alluvial fan follows the regional with decreasing elevation from sea level and it has sym- flow system. metric relationships to value of groundwater in mountain Figure 6 shows that the υDandυ18O values of all types areas with increasing elevation from sea level. of water in the study area plot to the right of the global Figure 5 shows that the stable isotope value in ground- meteoric water line (GMWL) of Craig (1961). This is also water has a vertical symmetric relation from sea level in typically characteristic of the mountain area in the North opposite directions, and coincides with the other chem- China Plain, which is probably due to isotopic enrichment ical factors such as pH and EC in the study area. The caused by evaporation that occurred before and during more depleted isotope values were observed in shallow infiltration in the recharge area. A similar observation

Copyright  2007 John Wiley & Sons, Ltd. Hydrol. Process. 22, 63–72 (2008) DOI: 10.1002/hyp CHEMISTRY AND STABLE ISOTOPES IN GROUNDWATER OF NORTH CHINA PLAIN 71

Figure 7. Hydrogeological cross-section of the study area with chemical characteristics (cross-section modiﬁed from Kleczkowski (1963))

et al was made by Chen . (2003) in Taihang Mountain of NO3 infiltration to the groundwater mainly occurred the North China Plain. in the agricultural suburb areas due to the excessive use The precipitation samples also plotted to the right of of fertilizer and irrigation. the GMWL with low deuterium excess d.Thed of all Groundwater recharges by precipitation and surface samples is lower than 10‰. The process of evaporation water infiltration in the mountain and surrounding pied- causes the slope of the meteoric water line to decrease. mont alluvial fan areas and discharges in lowland areas Precipitation affected by evaporation tends to have d in the North China Plain. Isotopic similarity of ground- values lower than 10‰(Yutsever, 1975). The enriched water in mountain and the deep layer in lowland areas isotopic values documented in the lower slope of the suggests that deep groundwater in lowland areas is part of study area could be result of the evaporation (Aravena the groundwater in mountain areas before flowing for dis- et al., 1999). tance in excess of about 100 km. In the other hand, deep The stable isotope composition of groundwater in the groundwater in lowland areas recharged from mountain local flow system reflected that of the precipitation in this areas. area, which seeps through the soil and unsaturated zone to Groundwater is recharged by precipitation and surface reach the water table. The similarity between the isotopic water in the mountains areas and flows to lowland areas composition of the shallow groundwater samples and the via the piedmont alluvial fan areas. During these pro- precipitation samples demonstrates this point. In the study cesses, groundwater flow separates in to two flows in the area, the equation υD D 5Ð88υ18O 18Ð27r2 D 0Ð854 mountain hill and piedmont alluvial fan. One is a local was obtained from groundwater; the data define a linear shallow groundwater flow system in th mountain hill and trend (r2 D 0Ð854) with lower slope (5Ð88) and lower piedmont alluvial fan areas, and other is a deep regional intercept (18Ð27) than the GMWL (υD D 8υ18O C 10) groundwater flow system. Groundwater coming from the of Craig (1961). The low slope of the groundwater mountain to lowland areas flowing through the deep layer trend relative to the meteoric water line is indicative in the piedmont alluvial fan follows the regional flow sys- of non-equilibrium in an environment of relative low tem. Mountain precipitation and surface water were the humidity (Clark and Fritz, 1997). Such an evaporation dominant mechanism for regional groundwater transport. trend is sometimes referred to as the local evaporation Also, there is a strong indication that groundwater has line (Gibson et al., 2005). a good correlation with dam water as a result of dam- water–groundwater interaction near the dam area in the western part of Beijing City. Regional groundwater flow was controlled by the continuity of large-scale, light υ18O CONCLUSIONS groundwater that originated from high altitude and high latitude areas and flows southeastward along the Chaobai In our study, it was found that the pH, EC and isotopic and Yongding River basin. value of groundwater have a symmetric variation from sea level in two opposite vertical directions. Groundwater flows under the elevation effect as precipitation, but faces a geographic effect in the shallow layer near the ACKNOWLEDGEMENTS surface. Other chemical characteristics are summarized We would like to thank Dr Li Fadong and Dr Yang Chong in Figure 7. from the Institute of Geographical Sciences & Natural Chemical patterns of ground waters evolve in the Resources Research, Chinese Academy of Sciences, for order Ca–Mg–HCO3 > Na–K–HCO3 > HCO3 –Na as their help during the fieldwork. This work was supported groundwater flows from the mountain to lowland areas. by MEXT through scientific grant no. 15310006.

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