Spatial characteristics of water quality, stable isotopes and tritium associated with groundwater flow in the Hutuo River alluvial fan plain of the North Plain

Yintao Lu & Changyuan Tang & Jianyao Chen & Xianfang Song & Fadong Li & Yasuo Sakura

Abstract The groundwater flow system and the flow on the aquifer by causing excessive groundwater abstrac- velocity in the alluvial fan plain of the Hutuo River, tion and irrigation return. China, have been studied, with an emphasis on relating geochemical characteristics and isotopes factors. Seven Résumé Le système d’écoulement de l’eau souterraine et la stretches of one river, six springs and 31 wells, with vitesse d’écoulement dans le plaine du cône alluvial de la depths ranging from 0 m (river waters) to 150 m, were Rivière Hutuo, Chine, ont été étudiés en mettant l’accent sur surveyed. The groundwater has a vertical two-layer les caractéristiques géochimiques et les facteurs isotopiques structure with a boundary at about 80–100 m depth, correspondants. Sept tronçons d’une rivière, six sources et yielding an upper and a lower groundwater layer. The 31 puits, ayant des profondeurs allant de 0 m (eau de la δ18O and δD values range from −10.56 to −7.05‰ and rivière) à 150 m, ont été examinés. L’eau souterraine a une −81.83 to −59‰, respectively. The groundwater has been structure verticale à deux couches avec une limite à environ recharged by precipitation, and has not been subjected to 80–100 m de profondeur, formant une couche supérieur significant evaporation during infiltration into the aquifer d’eau souterraine et une inférieure. Les valeurs de ∂ 18 Oet in the upper layer. Using a tritium model, the groundwater de ∂ Dvontde−10.56 à −7.05‰ et de −81.83 à −59‰, flow in the alluvial fan plain showed horizontal flow respectivement. L’eau souterraine a été réalimentée par les velocity to be greater than vertical velocity. Groundwater précipitations, et n’a pas été sujette à une évaporation in the upper layer is characterized by Ca–HCO3 type. significative au cours de l’infiltration dans l’aquifère de la From the spatial distribution characteristics of the stable couche supérieure. En utilisant modèle tritium, l’écoulement isotope and chemical composition of the groundwater, de l’eau souterraine dans la plaine du cône alluvial a montré agricultural irrigation was considered to have an influence une vitesse d’écoulement horizontal supérieure à la vitesse verticale. L’eau souterraine de la couche supérieure est caractérisée par un type Ca–HCO3. Du fait des caractéris- Received: 15 May 2006 /Accepted: 17 February 2008 tiques de la distribution spatiale en isotope stable et de la Published online: 12 April 2008 composition chimique de l’eau souterraine, l’irrigation fl ’ © Springer-Verlag 2008 agricole a été jugée avoir une in uence sur l aquifère en occasionnant des prélèvements d’eau souterraine et une restitution provenant de l’agriculture excessifs. Y. Lu ()) : F. Li Graduate School of Science and Technology, Resumen Se ha estudiado el sistema de flujo subterráneo y Chiba University fl Chiba 263–8522, Japan la velocidad de ujo en el cono aluvial del Río Hutuo, China, e-mail: [email protected] enfatizando las características geoquímicas y su relación con el contenido isotópico. Se relevaron siete tramos del río, seis C. Tang Faculty of Horticulture, Chiba University manantiales y 31 pozos, con profundidades que varían desde Chiba 271–8510, Japan 0 m (agua del río) hasta 150 m. El complejo subterráneo comprende dos capas con un límite a una profundidad J. Chen aproximada de 80–100 m, constituyendo una capa subterrá- Zhongshan University 18 Guangzhou 510275, China neas superior y una inferior. Los valores de δ OyδDvarían entre −10.56 a −7.05‰ y −81.83 a −59‰, respectivamente. X. Song Institute of Geographic Sciences El agua subterránea se recargó por lluvias, y no ha estado and Natural Resources Research sujeta a evaporación durante su infiltración en la capa Beijing 100101, China superior del acuífero. El modelo de flujo subterráneo, fl Y. Sakura utilizando datos de tritio, mostró que la velocidad del ujo Faculty of Science, Chiba University horizontal es mayor que la vertical. El agua subterránea de la Chiba 263–8522, Japan capa superior es del tipo Ca–HCO3. Teniendo en cuenta la

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1004 distribución espacial de los isótopos estables y la compo- This is one of the most important areas for both sición química del agua subterránea, se considera que el groundwater storage and human activity in China. Big riego para agricultura ha tenido influencia en el acuífero cities with huge population, e.g. Beijing, and debido al bombeo excesivo de agua y los retornos por riego. Handan are located in/near here (Fig. 1). Groundwater resources are the key to agricultural development, and the Keywords China . . Tritium . demand for groundwater will increase in this area. With Stable isotopes . Groundwater flow the development of the regional economy, the water use environment has changed. The groundwater level has lowered dramatically over the last half century owing to Introduction the over-pumping of groundwater and to drought, accom- panied by the expansion of saline-alkaline land area The North China Plain (NCP), located at 112°30′E– (Nakayama et al. 2006). 119°30′E and 34°46′N–40°25′N, is a thick Cenozoic A great many studies about chemical and isotopic sedimentary basin covering approximately 150,000 km2. characteristics of groundwater in the NCP have been

Fig. 1 Geomorphological map of the North China Plain (NCP)

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1005 reported. For instance, Chen et al. (2004) discussed the are: piedmont plain, alluvial fan plain, flood plain (alluvial distribution characteristics of the isotopic composition and plain) and littoral plain (Wu et al. 1996b; Fig. 1). In this average geochemical composition of groundwater in wells study, the focus is on the alluvial fan plain located in the of different depths throughout the NCP. Hutuo River plain. Based on the results of field surveys Geochemical characteristics change from recharge, and geochemical and isotopic analysis, the study empha- intermediate, to discharge zone according to the regional sizes the following aspects: (1) confirmation/quantification groundwater flow system (Stuyfzand 1999; Toth 1999; of the available groundwater resource using stable isotope Chen et al. 2004). The use of the geochemical method to (18O and D) measurements; (2) flow velocity of ground- estimate groundwater flow rates and mixing ratios is water recharged by modern precipitation using an expo- effective for the NCP (e.g. Chen 1988; Chen et al. 2002; nential model of tritium concentration; and (3) spatial Shimada et al. 2002). In the NCP, chemical patterns evolvement characteristics of stable isotopes and chemical evolve from the recharge to the discharge zone in the composition. The work involved field survey, water order: Ca–HCO3 >Mg–HCO3 >Na–Cl–SO4 (Chen et al. sampling and laboratory analysis, and provides a hydro- 2004). chemical background for protecting the water resource of Natural stable isotopes and radiogenic isotopes ((H, O, the alluvial fan plain in the NCP. 3H, 14C and 36Cl) of water have been widely used over the past several decades to address problems related to groundwater age, groundwater recharge, and delineation Study area and site description of flow systems in the NCP. Groundwater age from wells of 0–150 m depth in the NCP was estimated to be younger The North China Plain was formed over a long period of than 25,000 years using 18O data (Chen et al. 2004) and time by flooding and course changes of several rivers that from wells of 150–250 m and 341–456 m depth was which flow from the , or the Yanshan found to be 25,000 years and 30,000 years respectively Mountains, through the plain and into the (Wu using 36Cl data (Zhou et al. 2001). The tritium concentra- et al. 1996a; Fig. 1). The rivers have interacted with the tion in the NPC is high enough to be measured. In the flashy fluvial regime, and involve high sediment loads and recharge area, the tritium contents are more than 6 tritium frequent channel changes (Xu et al. 1996a). Each river units (TU), but they decrease to less than 1 TU along the played an important role in the formation of alluvial fans flow path in the littoral plain. Modern groundwater is then at the front edge of the piedmont plain zone and in the younger than about 45 years relative to the mid-1990s formation of the alluvial plains (Wu et al. 1996a). For (Clark and Fritz 1997). Several studies have been carried example, there are large fluvial fans formed by the Yellow out on groundwater age. For instance, Fritz et al. (1991) River, the Zhang River, the Hutuo River, the Yongding carried out a study for groundwater in the waterloo River, the and the . aquifer, Ontario, Canada. This study refined estimates for The study region is situated between a latitude 37°36′3″ groundwater mean residence time for water younger than to 38°39′28″ and a longitude 114°2′35″ to 115°29′24″ 30 years to within a decade. (Fig. 2), and is one of the alluvial fan plain zones (Hutuo There are four main geomorphological units in the River plain) mentioned above. The area has a continental, North China Plain. From the piedmont to the coast, they semi-arid climate with a mean annual temperature of 12–

Fig. 2 Location of the wells, river water and spring sampling sites in the study area

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1006 13°C, and summer maximum and winter minimum of third dividing points in some channels, those of the late 45.8 and −28.2°C, respectively (Wu 1992) and with Holocene still form the alluvial fans (Wu et al. 1996b). On annual precipitation of 400–800 mm (Yang et al. 2006). the alluvial fan plain, single channels are straight but the The precipitation is dominated by the Asia summer pattern of the channels is radial, which means that there is monsoon during July and August, which accounts for an apex at the top of a fan from which a number of about 70% of annual precipitation (Zhang et al. 2000). palaeochannels run in different directions (Wu et al. There is usually only 40–60 mm of rainfall, or even no 1996b). These palaeochannels are formed by the combi- rainfall, for more than 100 days in spring. The variation of nation of sand bodies of a number of meandering channels seasonal precipitation is so large that it is the common and are beaded in shape. The particle size is smaller; and case to have dry spring and flooding summer. Mean the sand layer is thinner (3–5 m) than those of the other potential evaporation ranges from 1,100 to 1,800 mm (Liu stage palaeochannels. Most of these palaeochannels lie and Wang 1992). between sandy elevated palaeochannel zones (Wu et al. Vertical distribution of the aquifer has been described 1996b). The alluvial fan plain surfaces and the uppermost in detail. A thick sedimentary sequence has been 10 m of sediments were formed by river deposits during deposited in the NCP, with a depth of 500–600 m in the late Holocene and are recorded in historical docu- depressions, 350–450 m in uplift areas, and 150–300 m ments. The lower sediments consist of micro cross-bedded around the alluvial fan (Zhou et al. 2001). These sedi- and trough cross-bedded medium and fine sand with grain ments of the Quaternary layer are composed of four sizes of 1–4 Ø, small gravels and pieces of brick. The layers: an unconfined layer of fine sand and silt to 40– upper sediments consist of horizontally bedded silt and 60 m depth; a confined layer of sand and gravel to 100– sandy soil (Fig. 4) with grain sizes of 3–6 Ø. The 150 m depth; a confined layer of course sand and gravel to radiocarbon age for these sediments is less than 250–350 m depth; and a confined layer of fine sand and 2,500 years BP (Wu et al. 1996a). gravel to bedrock at 400–600 m depth (Zhang et al. 2000; Chen et al. 2005; see Fig. 3). The alluvial fan plain slopes generally eastward from an altitude of about 100 m above Materials and methods sea level (m.a.s.l.) in the west to about 1–2 m in the east. During the late Pleistocene, the diversion points of the Water sampling and chemical analysis Hutuo River were located around Huangbizhuang, form- Groundwater of the alluvial fan plain zone in NPC was ing the old mountain front fan (Xu et al. 1996b). By the sampled during 1999–2000. Seven stretches of the Beisha late Holocene, the diversion points had moved down- River (a tributary of Hutuo River; samples collected at the stream to Gaocheng, forming a new alluvial fan. These base of Taihang Mountain and Beisha River were points around Gaocheng are along the NNE Anguo- considered as recharge to groundwater), six springs and Gaocheng fault (Shao et al. 1984). Alluvial fans were 31 wells with depths ranging from 0 m (river waters) to − 2 formed from which the palaeochannels are radially 150 m were surveyed (Fig. 2). The Cl , SO4 and NO3 distributed again. Although there are second, and even contents were analyzed by ion chromatography; K+,Na+,

Fig. 3 Hydrogeologic cross section along transect O–O’ in Fig. 1 (modified from Chen et al. 2005)

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1007

Fig. 4 Simplified hydrostratigraphic map of the alluvial fan

Ca2+,Mg2+ were measured by inductively coupled plasma 12.43 years (Unterweger et al. 1980). Atmospheric testing (ICP) with analytical precision of ±0.01 mg/l; and HCO3 of nuclear devices between 1952 and 1962 generated a was measured by titration with analytical precision of tremendous quantity of atmospheric tritium. The final year ±0.02 mg/l. of megaton tests generated a huge peak, which appeared in precipitation in the spring of 1963. So the curve from the input function for tritium will have a peak corre- Stable isotope analysis sponding to that time. Using this peak, one can get the 18O and deuterium (D) abundances are expressed as ratios mean residence time and infiltration rate of water. In in delta notation (δ) as per mil differences relative to the Denmark, Andersen and Sevel (1974) have shown that the standard known as the Vienna Standard Mean Ocean measured tritium profile in groundwater is the reverse of Water (VSMOW). They are defined as follows: the classic curve for tritium in precipitation. In general terms, consider that there is a parcel of R 18 sp groundwater in a regional aquifer. The composite of d OðÞ¼d D 1 1000 ð1Þ ’ Rst several years precipitation have contributed to ground- water through mixing in the unsaturated zone. In this 1 18 16 Where Rsp and Rst are the ratios for D/ Hor O/ O in the process, tritium content in groundwater will decrease by sample or standard respectively. δ18OandδDwere decay. The tritium concentration in this groundwater analyzed by a Delta S mass spectrometer with analytical parcel will be a function of its residence time in the precision of ±0.15 and ±1‰, respectively. recharge environment. The exponential model of tritium concentration is predicted by

Z1 A tritium profile peak and input function for tritium 1 in groundwater and tritium analysis CtðÞ¼ CRðÞt expðÞ exp d ð2Þ 3 T T Tritium ( H or T) is probably the most commonly 0 employed radioisotope used to identify modern recharge. l ¼ =T ¼ =sT It is a short-lived isotope of hydrogen with a half-life of 1 l In2 h

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1008 where Th is the half-life of tritium, T is the mean residence 2004), the groundwater was separated into a vertical two- time, CR(t) is tritium concentration in precipitation, and C layer structure (the upper layer and the lower layer) with a (t) is the recharged tritium concentration. If CR(t) can be boundary at 80–100 m depth. acquired, the mean residence time T will be calculated by C (t). The tritium content of water samples was analyzed by the Institute of Hydrogeology and Engineering Geology, Geochemical characteristics of groundwater Chinese Academy of Geological Sciences, Zhengding. and surface water Ion concentrations in the two layers were different − 2+ (Table 2). Cl ,Ca and NO3 ion concentrations were 2 + Results higher in the upper layer, and HCO3 , SO4 and Na ion concentrations were higher in the lower layer. Figure 5 Chemical and isotopic data of samples are shown in shows the relation between the major ion concentrations − 2 + 2+ + 2+ Table 1. The depths of the wells sampled are from 8.5 to (Cl , HCO3 , SO4 , NO3 ,Na,Ca ,K,Mg ) and the 150 m (Table 1). Based on vertical distribution of the depths of the wells in the alluvial fan. The major ions − 2 aquifer mentioned above (Yang et al. 2001; Chen et al. might be divided into three types: one type is Cl , SO4 ,

Table 1 Chemical and isotopic data of samples 2+ 2+ + + − 2 δ18 δ Sample/ Sample Well Ca Mg Na K HCO3 Cl SO4 NO3 O D Tritium site no. type depth (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (‰) (‰) (TU) (m) R1 River ― 31.94 12.1 4.94 2.37 65.47 3.57 81.32 10.44 −9.52 −66.18 22.23 R2 River ― 87.82 17.43 13.43 2.52 189.53 17.83 102.37 53.33 −8.75 −77.01 18.5 R3 River ― 95.81 20.58 19.54 2.64 195.27 32.1 105.24 72.73 −9.27 −78.57 21.59 R4 River ― 87.82 21.79 18.98 2.97 141.28 28.53 138.73 73.94 −7.51 −64.46 22.02 R5 River ― 67.86 18.64 9.17 1.72 189.53 15.69 66.97 40.16 −8.64 −72.26 21.87 R6 River ― 73.85 19.37 21.34 3.2 172.3 19.26 103.33 43.86 −8.54 −60.49 19.74 R7 River ― 72.65 20.58 6.52 1.37 183.78 7.85 74.63 40.97 −8.7 −73.38 21.05 G1 GW 8.5 127.74 27.84 21.06 3.01 189.53 39.23 162.65 150.56 −8.66 −74.32 23.85 G2 GW 24 95.81 35.10 22.35 1.27 344.59 44.94 66.97 35.16 −8.21 −68.09 38.84 G3 GW 25 183.12 36.29 52.98 5.32 384.40 72.20 147.44 60.97 −8.4 −59 26.8 G4 GW 25 127.74 34.38 31.58 2.55 402.02 46.37 116.72 17.82 −7.05 −72.74 23.51 G5 GW 27 71.86 21.79 18.52 1.53 195.27 17.83 100.46 32.32 −8.61 −68.3 26.59 G6 GW 28.5 85.83 13.31 13.80 0.73 229.73 28.53 62.19 25.32 −8.47 −72.89 30.83 G7 GW 30 87.82 24.21 26.89 1.17 246.96 39.23 114.81 64.33 −8.7 −64 15.6 G8 GW 30 211.36 47.58 88.19 4.69 367.30 284.20 85.52 11.20 −7.18 −62.06 21.22 G9 GW 30 57.03 23.59 35.74 7.77 185.50 60.63 57.97 0.00 −7.67 −59.06 15.65 G10 GW 31 73.85 21.30 14.07 0.91 206.76 28.53 79.41 26.30 −8.66 −76.83 31.29 G11 GW 34 65.87 9.68 9.92 0.88 212.50 21.40 23.92 12.67 −8.82 −78.99 19.07 G12 GW 35 101.80 67.78 41.39 1.11 476.69 92.73 81.32 28.99 −7.89 −60.48 21.36 G13 GW 40 93.81 19.58 15.56 1.55 298.65 32.10 49.75 ― −8.4 −64.3 28.1 G14 GW 40 41.00 45.00 29.10 1.11 313.00 34.00 11.00 ― −8.6 −65.2 23.5 G15 GW 40 191.54 41.35 25.47 6.15 294.85 53.94 140.79 ― −8.3 −65.2 25.2 G16 GW 40 94.00 67.00 41.50 1.89 407.00 62.00 165.00 27.78 −8.84 −72.71 24.15 G17 GW 40 35.00 42.00 12.40 1.95 315.00 36.00 15.00 0.00 −8.52 −66.25 14.75 G18 GW 45 95.01 33.89 21.97 1.77 292.90 21.40 108.11 47.81 −8.13 −75.36 22.93 G19 GW 50 24.27 18.89 60.69 1.52 284.60 1.66 20.16 ― −9.24 −68.82 16.29 G20 GW 60 66.46 36.83 22.27 2.72 304.61 57.95 2.69 ― −7.5 −59.7 12.2 G21 GW 70 51.10 19.37 16.73 1.32 235.47 32.10 7.65 5.61 −8.75 −80.72 11.15 G22 GW 80 22.00 39.00 15.90 0.86 263.00 25.00 5.00 ― −8.4 −66.4 9.4 G23 GW 80 56.19 13.45 12.80 2.54 216.25 16.47 30.67 ― −9.3 −68.62 11.89 G24 GW 80 26.38 16.35 63.05 2.66 294.85 12.44 28.66 ― −9.75 −72.69 7.53 G25 GW 100 70.30 28.98 14.75 2.47 296.80 31.43 68.61 ― −10.56 −81.83 10.96 G26 GW 110 64.13 29.92 47.77 2.75 269.70 56.20 27.79 ― −8.8 −64 1.9 G27 GW 120 34.63 17.81 70.55 3.93 213.60 92.30 76.66 ― −9.8 −70 0.4 G28 GW 135 34.65 23.16 250.55 1.87 693.19 30.51 266.26 0.10 −9.7 −72 0.4 G29 GW 120 62.00 67.00 94.30 1.80 335.00 60.00 180.00 ―–7.8 –64.3 6.4 G30 GW 130 55.47 18.05 24.63 5.97 183.10 6.80 25.24 7.77 –9.6 –63 5.3 G31 GW 150 84.08 46.84 148.03 5.83 265.07 101.02 336.90 ― −10.21 −76.97 3.91 S1 Spring ― 83.83 46.00 27.77 1.42 252.70 44.94 189.44 21.46 −8.95 −62.38 17.64 S2 Spring ― 89.02 29.05 17.13 2.05 246.96 28.53 120.55 20.80 −8.86 −58.95 18.43 S3 Spring ― 59.88 19.37 8.60 1.79 149.32 10.70 95.68 39.21 −8.81 −64.39 21.54 S4 Spring ― 49.90 19.37 9.20 1.42 229.73 3.57 28.70 45.18 −8.91 −61.26 22.54 S5 Spring ― 71.86 19.37 11.49 4.57 172.30 14.27 74.63 22.25 −8.8 −65.37 20.18 S6 Spring ― 87.82 21.79 4.79 1.35 212.50 10.70 79.41 6.09 −9.09 −81.42 19.42 GW groundwater from wells

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1009 Table 2 Statistics for the two layers of groundwater in the alluvial fan area (unit of ion concentration: mg/l) − 2 + 2+ + 2+ Layer Depth (m) Cl HCO3 SO4 NO3 Na Ca K Mg Upper layer 0–80 Min 1.66 185.5 2.69 0 9.92 22 0.73 9.68 Max 284.2 476.7 165 150.56 88.2 211.36 7.77 67.78 Lower layer 100–150 Min 6.8 183.1 25.24 0 14.75 34.63 1.80 17.81 Max 101.02 693.2 336.9 7.77 250.55 84.08 5.97 67

Na+ and K+, the second type is and Ca2+, and the third the upper layer, ion concentration decreased as the well type is NO3 . depth increased. However, nitrate was undetectable in the – fi fi The upper layer (0 80 m) is an uncon ned layer of ne lower layer. The difference in NO3 ion distribution sand and silt, and all ion concentrations varied widely. The between the two layers reflects a change in the influence − 2 + + concentrations of Cl , SO4 ,Na and K decreased as of human activities. 2+ − 2 the well depth increased. Likewise, HCO3 and Ca (the In the springs, Cl , SO4 , HCO3 and NO3 ion second water type) decreased with the well depth in this concentrations were 3.57–44.94 mg/l, 28.7–189.44 mg/l, layer. The lower layer (100–150 m) is a confined layer of 149.32–252.7 mg/l and 6.09–45.18 mg/l respectively. sand and gravel; depth 80–100 m is the boundary of the Na+,Ca2+,K+ and Mg2+ ion concentrations were 4.79– − 2 – – – upper and the lower layer. Cl , SO4 , Na+ and K+ ion 27.77 mg/l, 49.9 89.02 mg/l, 1.35 4.57 mg/l and 19.37 concentrations increased with the well depth, and there 46 mg/l respectively (Table 1). The range of ion was no significant increase in and Ca2+ ion concentration concentrations was close to the groundwater in the upper with increasing depth. Groundwater in this lower layer is layer, and springs were recharged by groundwater of the used because of the decline in the water table. upper layer. − 2 Nitrate is the most common water contaminant index In the river water, Cl , SO4 , HCO3 and NO3 ion for anthropogenic sources (Freeze and Cherry 1979). In concentrations were 3.57–32.1 mg/l, 66.97–138.73 mg/l,

− 2 + 2+ + 2+ Dashed lines Fig. 5 The distribution of ion concentrations (Cl , HCO3 , SO4 , NO3 ,Na ,Ca ,K ,Mg ) versus the depths of the wells. indicate the variation area of major ion concentrations

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1010

Fig. 6 The distribution of ion concentration in river water versus east longitude

65.47–195.27 mg/l and 10.44–73.94 mg/l respectively, −80.72 to −59‰ respectively. The δ18O values decreased δ and showed the highest NO3 concentration compared with with the well depth, but the change of D values was not that in the groundwater. Na+,Ca2+,K+and Mg2+ ion obvious. In the lower layer, the δ18O and δD values concentrations were 4.94–21.34, 31.94–95.81, 1.37–3.2 ranged from −10.56 to −7.8‰ and from −81.83 to −63‰, and 12.1–21.79 mg/l respectively (Table 1). Beisha River respectively. The δ18O and δD values decreased with the flows from west to east in the study area. Na+,Ca2+ and well depth in this layer. Groundwater in the upper layer all anion concentrations increased along river flow had greater δ18O than that in the lower layer. direction (Fig. 6). The δ18O and δD values in the river water ranged from −9.52 to −7.51‰ and −78.57 to −60.49‰ respectively and showed the lower isotopic values. On the other hand, Isotopic characteristics of groundwater the δ18O and δD values in the spring ranged from −9.09 to and surface water −8.8‰ and −81.42 to −58.95‰, respectively (Table 1). Stable isotopes of water are excellent tracers for recharge of surface water to groundwater (Craig et al. 2002). 18O and D are naturally occurring stable isotopes of oxygen Tritium characteristics of groundwater and hydrogen, respectively (John et al. 2002). Stable and surface water isotopes show different changes between the upper and Generally, the tritium contents of groundwater from wells lower groundwater layers (Fig. 7). In the upper layer, the are higher in the upper layer (7.53–38.84 TU) than in the δ18O and δD values ranged from −9.75 to −7.05‰ and lower layer (less than 11 TU; Table 1). River and spring

Fig. 7 The distribution of δ 18O and δ D versus the depths of the wells. Dashed lines indicate the variation area

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1011

Fig. 8 Relationship between δ 18O and δ D in the water samples. MWL (meteoric water line) is the relationship between δ18O and δDin meteoric water (δD=8δ18O+d; here d=0, −10). GMWL is MWL with d=10‰ water shows the higher tritium contents (greater than been subjected to significant evaporation during infiltra- 17 TU). tion into the aquifer. The intercept is often referred to as the deuterium-excess (d-excess), defined as d ¼ d D 8d 18O (Dansgaard 1964). The d-excess is a useful proxy Discussion for identifying secondary processes influencing the atmo- spheric vapor content in the evaporation-condensation The source of groundwater and surface water cycle in nature (Craig 1961; Merlivat and Jouzel 1979). Because most of the world’s precipitation is derived from The d-excess values of groundwater samples ranged from evaporation of seawater, the δ18O and δD composition of −10 to 10‰ in the upper layer and from 0 to 10‰ in the precipitation throughout the world is linearly correlated. lower layer (Fig. 8). It can be considered that the This relation is known as the global meteoric water line groundwater originates from rainfall with different d- (GMWL) and expressed as follows (Craig 1961): excess values. On the other hand, based on hydrology and d D ¼ 8d 18O þ 10. human activities, the upper flow system has been affected The δ18O and δD composition of all water samples in by many phenomena such as (1) location of Hutuo River the study region were plotted to the right of the global in the center of the alluvial fan plain, (2) excess irrigation meteoric water line (GMWL; Fig. 8). From the relation- water return flow to the aquifer. ship shown in Fig. 8, all of the points in the upper According to the study of Zhang et al. (2000), a δ18O groundwater layer were under the GMWL and the linear value of less than −9‰ signifies groundwater older than relationship is approximately parallel to the GMWL, 10,000 years in the NCP because the climate became showing that groundwater of study area has been warm 10,000 years ago. Whereas, if the groundwater is recharged by precipitation and these samples have not younger than 10,000 years, the δ18O value would be

Fig. 9 Relationship between δ 18O and tritium in the water samples

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1012 20 TU, implying that these samples were a mixture of new water and old water.

Groundwater flow system and flow velocity based on tritium Based on δ18O and δD values mentioned above, the range of ages in the two groundwater layers can be determined. Based on tritium values, modern groundwater age and flow velocity can be determined. As the era of bomb testing recedes further into the past, the tritium peak has either moved through actively circulating aquifers or has been attenuated by dispersion and mixing. Nonetheless, it may be preserved in some less active hydrogeological settings. The distribution of tritium suggests that ground- water in the alluvial fan plain above a depth of 150 m contains modern recharge water. However, modern re- charge only influences the shallow groundwater in the middle and the littoral plain and not the deep confined aquifers (Chen et al. 2003). The tritium concentrations in river water and groundwater had a strong exponential Fig. 10 The distribution of tritium versus the depths of the wells. dependence relation to well depth in the upper layer Dashed lines indicate the variation area (Fig. 10). The tritium value reached a peak at 20 m depth, in which it is 40 TU. Then, tritium values decreased as the well depth increased. The lowest value was 7.53 TU in the upper layer; in the lower layer the lowest value was less greater than −9‰. In the upper layer, δ18O values of than 15 TU. samples were higher than −9‰ except G19, G23 and On the basis of data from the International Atomic G24; in the lower layer, δ18O value of G29 and G26 was Energy Agency (IAEA), the distribution graph of tritium higher than −9‰, and the others were lower than −9‰ concentration in global meteoric water can be described. (Fig. 9). It can be considered that groundwater in the Based on tritium values of river water in Fig. 10, tritium upper layer and groundwater of G29 and G26 in the lower concentration of rainfall in the NCP was 18–22 TU. In layer was younger than 10,000 years (modern water) in addition, modern water (groundwater in the upper layer; the alluvial fans. In the NCP, the tritium value of rainfall Fig. 9) was supplied by modern rainfall. In this study, it is that is older than 10,000 years is considered to be close to considered that groundwater is recharged from rainfall and 0 TU, so the groundwater in the lower layer is a mixture the peak value of tritium contents is due to the of new water and old water. Almost all river water and atmospheric testing of thermonuclear bombs between spring water is younger than 10,000 years, except R1, R3 1952 and 1962. Using the model described in Eq. (2) the and S6. Tritium values of R1, R3 and S6 were higher than tritium input can be determined on the basis of measured

Fig. 11 Tritium distribution in groundwater of a the upper layer and b the lower layer versus east longitude. Dashed lines indicate the variation area

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1013

Fig. 12 The vertical distribution of δ 18O(‰) in groundwater along transect O–O’. Arrows shows the flow direction tritium data. From the model, it can be considered that the tritium concentration. By the exponential model, it can be vertical velocity of groundwater in the upper layer is less calculated that horizontal flow velocity is faster than than 1 m/year. vertical velocity. Tritium contents decreased as latitude In the upper groundwater layer, tritium contents of increase in the lower layer (Fig. 11b). It is considered that horizontal distribution (along O–O` in Fig. 2) reached a the flow direction of groundwater in the lower layer is peak at about 114.5° E (Fig. 11a). As mentioned above, an from west to east, so tritium contents decrease with the exponential model can be educed from the distribution of groundwater flow.

Fig. 13 Piper diagram for the major ions in groundwater (from wells), river water and spring water in the study area

Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3 1014

Fig. 14 The vertical distribution of the hydrochemical composition of groundwater along transect O–O’

Spatial evolvement characteristics of stable isotopes type is probably related to ion exchange between and chemical composition groundwater and groundwater that is mainly excess Because the groundwater level is higher in the mountain- irrigation return. Every time the return water re-percolates ous areas, groundwater constantly flows into the plain, and through the soil profile, it dissolves more salts, resulting in the mountainous area plays an important role as a recharge the mixed chemistry as shown in Fig. 14. region (Nakayama et al. 2006; Fig. 12). In the NCP, almost all of irrigation water is pumped up from underground. The excess irrigation water returns to the Protection of the groundwater resource aquifer by infiltration. Because it infiltrates into the aquifer The NCP is one of the most important agricultural areas in directly, evaporation and oxygen isotope shift have less China. Groundwater storage and quality are affected by influence on it. The δ18O values of the groundwater in agricultural irrigation and industrial development. Because some places (e.g. G19, G23 and G24) were low compared the agricultural irrigation water and some industrial and with most places in the upper layer (Fig. 12). This implied domestic use water come from aquifers, the groundwater that the irrigation has an influence on the aquifer. There level has a downward trend and water quality is getting are a lot of irrigation wells in the alluvial fan plain leading worse. NO3 concentrations from about 18% of water to excessive groundwater use as well as irrigation return samples were higher than the water quality standard for (water returned to the aquifer after use). drinking water sources (NO3 : 44 mg/l; Ministry of Health The Piper diagram (Piper 1944) is the most widely of the People’s Republic of China 2006; Table 1). The used graphical form to express geochemistry results and it authors herein suggest that management of the groundwa- is quite similar to the diagram proposed by Hill (1940). ter resource includes three points. Firstly, irrigation The diagram displays the relative concentrations of the management should be carried out under scientific major cations and anions on two separate trilinear plots direction; good planning of irrigation in dry years is (Güler et al. 2002). The points of the central diamond are especially important for saving water (Yang et al. 2006). from the two trilinear plots (Güler et al. 2002). The central Secondly, the management system of industrial and city diamond-shaped field is used to show overall chemical water use should be optimized; and thirdly, the monitoring character of the water (Hill 1940; Piper 1944). Figure 13 of wastewater discharge and disposal should be intensified. is a Piper diagram showing the results of the river, spring and well samples in the alluvial fan plain. The river and spring waters were distinctive in their low concentrations Conclusions + − of Na and Cl and the type was HCO3–NO3–Ca. Because of the effect of carbonate rock and metamorphic rock in In this study, water quality, stable isotopes and tritium the mountains region (Fig. 4), groundwater in the upper were used to determine the groundwater flow path. The layer was characterized by Ca–HCO3. On the other hand, main findings can be summarized as follows: groundwater points in the lower layer were broadly distributed rather than forming distinct clusters. Ground- 1. The δ18OandδD values ranged from −10.56 to water in the lower layer was classified into two dominant −7.05‰ and −81.83 to −59‰ respectively. The water types: HCO3–Ca–Mg and HCO3–Na–K. groundwater in the upper layer originates from rainfall In the discharge area, groundwater was characterized with different d-excess values, and has not been fi fi by Na–HCO3 type (Fig. 14). Formation of this chemical subjected to signi cant evaporation during in ltration

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Hydrogeology Journal (2008) 16: 1003–1015 DOI 10.1007/s10040-008-0292-3