Environ Earth Sci (2010) 61:1037–1047 DOI 10.1007/s12665-009-0425-6

ORIGINAL ARTICLE

Holistic assessment of groundwater resources and regional environmental problems in the North China Plain Jianyao Chen

Received: 14 March 2009 / Accepted: 23 December 2009 / Published online: 28 January 2010 Ó Springer-Verlag 2010

Abstract Water balance components of the North China Plain (NCP) were analyzed, indicating the decrease both in precipitation and evaporation. The decreased precipitation and expansion of water use for agriculture, industrial and domestic purposes have caused a water crisis, which was managed until now by diverting water from the Yellow River and over exploitation of groundwater. The groundwater resource was assessed by estimating its recharge in both upper unconfined and lower confined layers, yielding a total value of 1.65 9 1010 m3/a. Total groundwater use was estimated and judged by the actual water table drawdown. Salt accumulation, water table decrease, fluoride and nitrate pollution were all found to be major regional environmental problems. Furthermore, heavy metals were found in high content in the soil and surface water in suburbs of large cities, posing a potential risk of pollution in the groundwater. It has been verified by isotropic data that dry conditions have occurred since 10 ka and are therefore part of the natural process. Possible solutions for water crises in the NCP are proposed. Keywords Water balance  Groundwater  Recharge  Isotope  Water deficit  North China Plain Electronic supplementary material The online version of this article (doi:10.1007/s12665-009-0425-6) contains supplementary material, which is available to authorized users. J. Chen School of Geography and Planning, Sun Yat-sen University, 510275 Guangzhou, China Present Address: J. Chen (&) CSIRO Land and Water, GPO BOX 1666, Canberra, ACT 2601, Australia e-mail: [email protected]

Introduction The North China Plain (NCP), located in eastern China between 35°000 –40°300 N and 113°000 –119°300 E, is bounded by the Taihang Mountains to the west, the Yanshan Mountains to the north, the Bohai Sea to the east, and the Yellow River to the south. The plain was formed through fault subsidence since the Cenozoic and deposition of Quaternary sediment 400–600 m thick by the Yellow River and other main rivers (Fig. 1). Encompassing Beijing, Tianjin, and Hebei Province (referred to here as BTH) and northern parts of Henan and Shandong provinces in the lower reaches of the Yellow River (LYR), the NCP is an important agricultural region. Approximately 1.06 9 108 people live in the NCP (1995). Of its large area of *17.87 9 104 km2, 12.87 9 104 km2 are in BTH, 2.9 9 104 km2 are in Shandong Province, and 2.1 9 104 km2 are in Henan Province (Lin et al. 2000). There are four main geomorphologic units in the NCP from the Taihang Mountains to the Bohai Sea: mountain and piedmont plain, alluvial fan plain, flood plain, and coastal plain (Wu et al. 1996). These units are closely associated with various zones of the groundwater flow system. The recharge zone (RZ) of downward flowing groundwater occurs in the mountain and piedmont plain, while the discharge zone of upward flowing groundwater is found in parts of the flood plain and coastal plain (Fig. 8, ESM only, Zhang et al. 2000a). The alluvial fan plain and part of the flood plain correspond to an intermediate zone, where groundwater passes through the RZ to the discharge zone. Field surveys and geochemical analyses of groundwater samples have found a two-layered structure of groundwater in the NCP, with a boundary at about 100– 150 m depth (Chen et al. 2004b). The upper layer (UL) corresponds to the unconfined and/or semi-confined

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Fig. 1 Geomorphological units of the North China Plain, modified from Wu et al. (1996)

aquifer, while the lower layer (LL) corresponds to the confined layer, to which groundwater is replenished from the RZ. The Yellow River, which serves as the southern boundary of NCP, is a suspended river and thus recharges the nearby aquifer due to its relative height. Annual precipitation ranges from 400 to 600 mm in the NCP, with potential evaporation of about 1,000 mm. About 70% of the total precipitation occurs during the Monsoon season from June to September, with only 10% falling from March to May. Evapotranspiration from a winter wheat field from March to May can be as high as 6 mm/day (Wu et al. 1997). In response to such seasonal rainfall, the groundwater table is generally highest in summer and lowest in spring. The NCP contained about 8.84 9 104 km2 of arable land in 1995, of which 6.02 9 104 km2 were in BTH, 1.672 9 104 km2 were in Shandong Province, and 1.152 9 104 km2 were in Henan Province (Lin et al. 2000). Cereal crop production dominates the land, with wheat grown from October to June and corn and soybeans grown from June to September. Agricultural activity in the NCP has generally remained constant over the last 20–30 years, although the expansion of major cities has consumed much agricultural land, and cereal crops have been replaced by vegetable crops around major cities. Groundwater is

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commonly used for irrigation in the NCP during critical crop periods, except where a surface water supply is available, such as in the LYR (Chen et al. 2001). The groundwater table has decreased continually over the last 30 years, especially in BTH, mainly due to overexploitation of groundwater for agricultural uses (Chen (JY) et al. 2003). Information on the changes in groundwater depth in BTH since January 2006 can be obtained online at http://sqqx. hydroinfo.gov.cn/shuiziyuan/start.aspx?curtype=HHH. Many studies have examined and assessed water use in the NCP since the 1980s and have produced numerous reports and publications. However, many of these studies have focused on either BTH or the LYR, which have medium-to-deep and shallow groundwater depths, respectively. In contrast, few comprehensive datasets are available for the entire NCP (e.g., Chen et al. 2007a). For such an important region of China in terms of food and water security, reevaluations of groundwater resources and environmental problems under the pressure of human activities and climate change are crucial, especially since assessments and predictions have varied and deviated from the real situation over the last 20 years. Thus, here, we reevaluate groundwater resources synoptically in terms of groundwater quality and quantity and to provide a holistic view of groundwater development, environmental problems, and solutions to water crisis in the NCP.

Water balance analysis Precipitation Generally, precipitation is the primary source of natural recharge to the NCP aquifer, and precipitation variations cause seasonal and annual fluctuations of the groundwater table. Annual average precipitation at 20 meteorological stations has tended to decrease since the 1980s (Fig. 9, ESM only). Decadal average precipitation values were 620, 611, 589, 539, and 568 mm in the 1950s, 1960s, 1970s, 1980s, and 1990s, respectively, and the annual average for the whole period was 570 mm. The standardized difference (SDP) from the average precipitation (AP) was calculated as SDP ¼ ðXi  APÞ=AP where Xi is the original precipitation, and SDP was summed cumulatively, showing increasing, relatively stable, and decreasing trends for the periods 1951–1964, 1965– 1977, and 1978–2001, respectively (Fig. 9, ESM only). Evaporation Potential evaporation can be determined by either measurements of pan evaporation or estimations under wet

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circumstances using empirical or theoretical formulas, such as the Food and Agriculture Organization (FAO) and Penman–Monteith equations. In this study, evaporation (ET) in the NCP was estimated by the method proposed by Xu et al. (2005) (referred as Xu’s method hereafter), with the impact of ground heat flux ignored. This method yielded annual ET series, ETb, which varied by approximately 300–400 mm from the average but had a similar decreasing trend. Jinan station showed the highest ETb, while Shijiazhuang, Anyang, and Xinxiang had the lowest values; the annual average potential ET was 1,410 mm. The SDP from the average ETb (SDE) was defined in the same way as SDP. Figure 10 (ESM only) presents the SDE values, which clearly indicate the decrease in ETb since 1981. Fluctuation of ETb impacts water use in the lower river reaches and the NCP. The decreasing trend suggests that water use may have decreased in response to the similarly decreasing trend in precipitation. Actual evapotranspiration (AET) can be measured directly in the field using a lysimeter or estimated by multiplying pan evaporation (of various sizes, such as U20 of 20 cm in diameter or E601) by the crop factor (Kc). Annual AET estimated from lysimeter measurements from 1987 to 1996 at Yucheng, near Jinan, was approximately 941 mm. Monthly lysimeter measurements of ET at Yucheng (ETl) and ETb were used to calculate the Kc (Kc = ETl/ETb; Fig. 2); the results were then used to estimate actual ET in the NCP. The NCP and especially the LYR area have been affected by the diversion of Yellow River water since 1972 and by land use and cover changes following the ‘‘reform and open’’ policies begun around 1980. Thus, AET was calculated only for 1981–2000 (Fig. 11, ESM only). The annual average AET in the NCP for this period was 796 mm, which was 145 mm less than that measured at Yucheng. The annual average deficit for crop production can thus be obtained as 796 (539 ? 568)/2 = 238 mm.

Kc=ETl/ETb

1 0.8

Recharge from precipitation to the UL aquifer Water balance components were analyzed based on a 10year series of experimental data obtained at Yucheng Station of the Chinese Academy of Sciences (CAS), where the ratio of annual precipitation to AET was approximately 0.63, indicating that a water deficit of 37% could be supplied from diverted Yellow River water if runoff is negligible (Chen et al. 2004a). Evaporation from the water table was estimated to contribute to 17% of AET according to data measured by weight lysimeter (Chen et al. 2004a). Since the groundwater table in the LYR has remained relatively stable, the 17% can be interpreted as equivalent to the percolation or recharge to the aquifer from precipitation. The average recharge rate from annual precipitation in NCP areas of Hebei Plain, Henan Province, and Shandong Province was estimated to be 0.1533, 0.168, and 0.1526, respectively, based on data provided by Zhang and Li (2005). Since the BTH, Henan Province, and Shandong Province account for 72, 11.8, and 16.2% of the total area of the NCP, respectively, the average recharge rate was calculated as 0.155 using area weighting. Recharge from precipitation to the LL aquifer The confined aquifer in the LL is primarily replenished by lateral flow from the RZ and flow from the UL through the leakage layer. Leakage from the UL is hard to judge, and this component is already included in the recharge from precipitation. Thus, only precipitation supplied to the LL in the RZ is discussed here. Using data reported by Zhang and Li (2005), the water recharged to the LL from precipitation was estimated to be 1.29% in the Hebei Plain, assuming that the entire area could be recharged. If the area of the RZ was used, the above result should be multiplied by a factor of 3–5, yielding a rate of 3.9–6.5%. Lateral flow from the piedmont to the NCP was estimated as 112.5 mm based on tritium and water balance calculations (Chen (JY) et al. 2003); the figure represents approximately 20% of annual average precipitation. As noted above, 15.33% was estimated as the UL recharge rate for the Hebei Plain; the remaining 4.67% could therefore have recharged the LL. Other components

0.6 0.4 0.2 0

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Month Fig. 2 Monthly Kc, defined as the ratio of evapotranspiration measured by lysimeter (ETl) to ETb calculated by the Xu’s method

Chen (1997) reported that the runoff coefficient was less than 0.15 even in the wet years of 1961–1964, and the annual average was as low as 0.013 in the LYR. In the BTH, runoff was estimated as 8% based on data from 1956 to 1984, while 71.4% was stored in the unsaturated zone as soil moisture, and 20.6% was recharged to the aquifer (Fang et al. 1993). Of the total precipitation, 78% was used

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as ET; i.e., 6.6% of precipitation recharge was supplied to the unsaturated zone through the capillary fringe, and the net recharge rate was approximately 14%. The annual average discharge (AAD) in the NCP could thus be estimated as: AAD ¼ 17:87  104 km2  570 mm  8% ¼ 8:15  109 m3 : This value is close to the normal flow rate of the Haihe River that discharges to the sea near Tianjin (7.6 9 109 m3; Fang et al. 1993). While no measurement data have been collected on groundwater discharge to the sea, this discharge was estimated to be 4.77 9 108 m3 in the NCP (He and Zhang 2005), i.e., 6.28% of the river discharge to the sea or 0.5% of precipitation. The contours of the water table in the NCP clearly show an east to northeastward flow direction toward Bohai Bay, while the Yellow River recharges nearby areas of the aquifer (Fig. 12, ESM only). In the lower reaches of the approximately 780 km long Yellow River, groundwater flow flux to the NCP was estimated as 0.18– 0.62 9 108 m3/a (Chen et al. 2007a). Assuming an impact zone along the river of 20–40 km (Chen et al. 2005a), the recharge rate from the Yellow River in the impact zone would be 0.58–3.97 mm/a, which is in the same order of magnitude as that discharged to the sea from the whole plain (2.85 mm).

Development of groundwater resources The NCP contains 11% of China’s population and 14% of its arable land, and produces 14 and 13% of the nation’s gross domestic industrial and agricultural products, respectively. At the same time, the NCP has only 1.9% of China’s total water resources (Xie et al. 2002). Water resource per hectare of arable area is approximately 13.6% of the national average. Increasing demands have led to greater development of groundwater resources in the NCP, and the amount of groundwater exploited in Hebei Province alone accounts for approximately 20% of the total groundwater exploited in China (Zhang and Li 2005). Groundwater resource surveys and assessments were carried out in the NCP in the early 1980s and from 2000 to 2003. However, the reports and papers resulting from those studies have provided varying assessments of the groundwater resources in the UL and LL layers. According to the first survey, annual average recharge in a 1.39 9 105 km2 area, approximately equivalent to the BTH, was 2.66 9 1010 m3, and the amount with a mineralization level of \3 mg/l available for exploitation was about 1.96 9 1010 m3. In the BTH, a specific value of 1.30 9 1010 m3 was given as the groundwater resources available for

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exploitation (GAE) (Zhang et al. 2000b). Based on the second survey, GAE in the BTH was estimated to be 1.39 9 1010 m3 (Zhang and Li 2005). The different findings for GAE are likely due to the diversity of the area and variations in the data period and definition of GAE. Thus, despite previous efforts, it remains unclear how much water is recharged to the aquifer and how much is available for exploitation. It is, therefore, necessary to evaluate the recharge in the NCP using a synoptic approach based on the water balance analyses described in the previous section. Values for the annual average water recharged to the UL in the BTH (WBTH) and in the LYR (WLYR) were calculated using a percolation rate of 0.155: WBTH ¼ 12:87  1010 m2  570 mm  0:155 ¼ 1:1  1010 m3 WLYR ¼ 5:0  1010 m2  570 mm  0:155 ¼ 4:3  109 m3 : Water recharge mainly to the LL (WLL) was calculated by assuming that the RZ encompasses one-fourth of the total area: WLL ¼ ð1=4Þ  17:87  1010 m2  570 mm  4:67% ¼ 1:19  109 m3 : Total recharge in the NCP (WTOTAL) was then calculated by summing the above components: WTOTAL ¼ WBTH þ WLYR þ WLL ¼ 1:65  1010 m3 : Determining how much water is being exploited annually from the aquifer compared to the GAE is more difficult. While various amounts have been estimated, none have been conclusive. For example, groundwater exploited in the Hai River basin, equivalent to the BTH, was estimated to be 2.7 9 1010 m3 in 1988 (Foster et al. 2004) and 1.58 9 1010 m3 in 1990 (Zhang et al. 2000b). We can separate groundwater development in the NCP into three stages: the relatively steady water table stage before 1964, preliminary decrease in the water table and formation of a temporary depression cone from 1965 to 1975, and obvious decrease in the water table and appearance of an enduring depression cone after 1975 (Zhang et al. 2000b). There were 8.56 9 105 tube wells in the Hebei Plain (excluding Beijing and Tianjin) in 2000 (Zhang and Li 2005), creating a density of 4.5 tube wells per square km. Over pumping caused the water table to decrease by 0.72 m on average from 1975 to 1999 at Luancheng; such decrease was typical for the piedmont area of the NCP (Chen (JY) et al. 2003). The average rates of decrease in the UL of Hebei Province during 1975–1980, 1980–1985, 1985–1990, and 1990–1999 were estimated to be 0.1, 0.536, 0.162, and 0.508 m/a, respectively; while the rates in the LL in the

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same periods were 0.694, 2.0, 0.472, 1.39 m/a, respectively (Zhang and Li 2005; Fig. 3). The water deficit, estimated by the previous water balance analysis, is used here to estimate the water supply needed. AET varies spatially in the NCP and tends to decrease from south to north. The annual average deficit of 238 mm estimated for the last 20 years is lower than the practical irrigation rate of 300–450 mm. Approximately 20% of irrigation water is recharged to the aquifer depending on the irrigation method, and thus 250 mm of irrigation water is appropriate as the net minimum requirement for yielding the total water required for agricultural use in the NCP: 250 mm  8:84  104 km2 ¼ 2:21  1010 m3 : Total groundwater used in the NCP comprises of 71, 18, and 11% for agricultural, industrial, and domestic purposes, respectively (Chen and Ma 2002; Zhang et al. 2006). Total groundwater use was calculated as 3.11 9 1010 m3 and regarded as the minimum groundwater requirement. The difference between this value and WTOTAL is balanced by both diversion from the Yellow River in its lower reaches and exploitation of stored groundwater, especially in BTH. Over the last 20 years, an annual average of 1.28 9 1010 m3 of water has been diverted in the LYR, with an additional *2.0 9 109 m3 diverted to Hebei Province and Tianjin; thus, a total of 1.48 9 1010 m3 of Yellow River water has been diverted for use in the NCP (Chen et al. 2005a). Although the sum of diverted Yellow River

Fig. 3 Changes in the water table in nine main cities in Hebei Province from 1975 to 2000; the vertical segment indicates spatial variations. Modified from Zhang and Li (2005)

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water and WTOTAL yields a value close to the minimum groundwater requirement, the real situation is made complex by uneven spatial and temporal distributions. Nonetheless, more even allocation of Yellow River water in the NCP, not only in the LYR, should be a goal to reduce the continuous drawdown of the water table in the BTH, despite practical difficulties related to administrative barriers. Table 1 lists the water recharge and water use separately for the BTH and LYR. The water deficit at Yucheng, which has a shallow water table typical for the LYR, was estimated by 941–570 = 371 mm, as mentioned above; however, the irrigation rate in this region is as high as 454 mm for 128 9 108 m3/(6.02 9 104 km2). An extra 81 mm is lost either to evaporation from the water surface or as drainage. As stored groundwater resources have been developed, the water table has been drawn down by 0.5 m annually on average in both the UL and LL of the BTH. Given a specific yield of 0.1, the water supplied from stored water can be calculated as 12:87  104 km2  0:5 m  0:1 ¼ 6:44  109 m3 : This estimation agrees well with the water deficit of approximately 7.0 9 109 m3 in the BTH shown in Table 1.

Water quality and environmental issues The spatial pattern of water quality in the NCP was analyzed according to the three hydrogeological zones combined with the UL and LL layers described by Chen et al. (2005b). Generally, freshwater exists in the LL recharge, intermediate, and discharge zones, but is limited to the UL of the RZ. Chemical facies evolve from [Ca ? Mg][HCO3] to [Na][SO4 ? Cl] types in both the UL and LL. Since Cl is relatively conservative as groundwater flows from the recharge to discharge zones, it is used to depict the spatial pattern of water quality in the NCP (Fig. 4; Fig. 13, ESM only). The UL in the eastern part of the NCP had a Cl concentration greater than 250 mg/l, which is considered the upper maximum for drinking water. The groundwater in the LL of the NCP can be used as drinking water except in the coastal plain, where the Cl concentration exceeds 400 mg/l.

Table 1 Water recharge and water use in the NCP from 1981 to 2000 Region

Water resources (9108 m3)

Water use (9108 m3)

BTH

Groundwater: 121.9, Yellow River: 20

Groundwater is the main source; agricultural use: 150.2; total 212

YLR

The Yellow River is the main source: 128

The Yellow River: 128; the groundwater table is relatively stable

Water resources and uses in the NCP were obtained mainly from the synoptic water balance analysis, and the deficit estimated in the BTH closely matched with changes in groundwater storage. The possible use of surface water for irrigation in areas near the dam and/or river, the use of waste water from city sewage, and the parameters assumed for the water balance analysis might have contributed to errors of less than 10%

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Fig. 4 Spatial distribution of Cl in the upper layer (UL) groundwater of the NCP

The groundwater flow system, in which Cl generally accumulates in the discharge zone, as well as seawater intrusions over the past 15,000 years has affected the spatial distribution of water quality. The areas in which Cl concentrations exceed 1,600 mg/l in the UL or 400 mg/l in the LL correspond well with the coastal plain, which has experienced seawater intrusions, especially around 6 ka before present (BP), when high sea levels inundated areas 100 km inland (Zhang et al. 2000b). The spatial distribution of Cl in the UL clearly indicates the effect of the Yellow River, with relatively low Cl concentrations found in areas near the river. Large water table drawdown has occurred around urban areas. With freshwater limited in the UL and perched aquifers, drawdown has especially affected intermediate and discharge zones of the LL, as illustrated in Fig. 3; the sharper water table decrease in the LL than in the UL (Fig. 3) can be explained partly by the spatial distribution of water quality. Water quality, water table drawdown, and salt accumulation in the eastern NCP are closely associated with each other. While the water table has dropped more than 25 m in the UL of the RZ, it has dropped more than 50 m in the LL of the intermediate and discharge zones (i.e., the middle and eastern parts of the NCP) compared to levels examined before 1964 (Zhang and Li 2005). Grain yield per hectare has decreased along a cross-section of 38°N from the Taihang Mountains to

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Bohai Bay (Kaneko et al. 2005), and groundwater quality plays a key role in this phenomenon. Salt accumulation in the vadose zone prevails in the lower river reaches and coastal plain. Although irrigation water diverted from the Yellow River helps reduce the Clcontent in the main root zone of crops, large average values and variations of the Cl- concentration were found in a vertical profile of 0.3–10 m at Yucheng (Chen (JY) et al. 2002). Rainfall and irrigation are the main factors in variations of the Cl- concentration, as these factors can change the water potential abruptly along the profile, resulting in redistributions of water and ion concentrations, i.e., flushing Cl- from the UL to the LL. Other factors such as evaporation also contribute to redistributions but in a milder, more consistent manner, causing upward movement of water and ions. In the early 1990s, the annual average application of fertilizer in China was approximately 191 kg N/ha (Huang and Liu 1995). However, in the NCP, the average was 417 kg N/ha, with a range of 280–597 kg N/ha (He and Jiang 1996). A case study of fertilizer application in Shandong revealed an average of 458.2 kg N/ha for the period 1990–2002 (Wang et al. 2006). Over-application of fertilizer causes not only nutrient loss to the atmosphere but also groundwater pollution caused by nitrate leaching. A comparative experiment revealed obvious nitrate leaching in

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40

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wastewater

delta

N in per mil

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plots fertilized at 400 and 800 kg N/ha (Hu et al. 2001). A plot experiment suggested annual optimal fertilizer applications of 200 kg N/ha for winter wheat and corn in the NCP (Hu et al. 2006), while a model simulation suggested 240 kg N/ha (Huang et al. 2001). Nitrate pollution in groundwater of the NCP is related not only to the excessive application of N-based fertilizer, but also to the geological setting, characteristics of the groundwater flow system, and land and water uses. Fertilizers and human wastes are the principal N sources, while aquifer and groundwater flow characteristics control nitrate accumulation patterns. Nitrate pollution has been found at depths as low as 100 m in the NCP, i.e., in the UL (Chen et al. 2005b) (Fig. 14, ESM only). Aquifer pollution has also been found to depths of about 50 m in the RZ; the dominant nitrate concentration is less than 100 mg/l with an average of 45.3 mg/l for groundwater and 29.2 mg/l for springs. The serious pollution in this zone is a result of the large population, industrialization, and dependence on groundwater. In the LYR, where large amounts of river water are brought in, only the upper aquifer layer (less than 8 m thick) contains nitrate. Although nitrate concentrations are high in the unsaturated zone, because of the upward potential gradient, nitrate is not easily transported downward in the flow field. No significant nitrate pollution was found in the intermediate zone or along the coast in the discharge zone due mainly to the high salinity of the groundwater and the lack of freshwater for irrigation, both of which limit extensive agriculture in those areas. Previous studies have reported that d15N ranges from 10 to 22% for manure/urine sources and 2 to 9% for natural soil organic-N sources (Kreitler and Jones 1975; Heaton 1986; Clark and Fritz 1997). Fertilizer normally has a d15N value close to 0% air. Isotope 15N data have been used to identify the sources of nitrate pollution in NCP groundwater since 1990 (Fig. 5). Samples in 1991 and 2001–2002 in wastewater and irrigation areas were collected near Shijiazhuang City, Hebei Province, and in the delta area in 2003 and 2004. Figure 5 indicates that in 1991, nitrate mainly reflected a mixture of two sources: soil organic-N and fertilizer. However, by 2001–2002, obvious nitrate sources include untreated domestic wastewater and leakage from manure/urine pits. The nitrate concentration in groundwater increased within approximately 10 years. Denitrification does not occur near Shijiazhuang, since it is located in the RZ, in contrast to the Yellow River delta area, which is basically a discharge zone with a reduction environment and relatively high d15N values. High fluoride content in the groundwater is another regional environmental problem in the NCP, which may cause fluorosis resulting in pathological change of bones and teeth by prolonged use of water with fluoride concentrations greater than 1 mg/l. It was estimated that

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LN(NO3) in mg/L Fig. 5 Relationship between d15N and ln(NO3) in the North China Plain. Data sources: ‘‘1991’’ and ‘‘2001–2002’’ datasets from Zhang and Guo (2005); ‘‘wastewater’’ data (also sampled in 2001–2002) by Chen et al. (2006); and ‘‘delta’’ data reported by Chen et al. (2007b)

approximately 45 million people in China, particularly in the north, used high-fluoride-bearing water as drinking water (Xu 1988). The chemical composition of soil mass was found to be one of the fundamental factors affecting fluoride content in the groundwater with the other factors given as paleogeography, climate, seepage, and hydrogeochemical conditions (Liu and Zhu 1991; Ren and Jiao 1988). Spatial distribution of fluoride in groundwater is related to the groundwater flow system in the NCP, i.e., shallow high fluorine groundwater in the intermediate zone and deep high content in the discharge zone (Ren and Jiao 1988). This pattern is also consistent with the chemical facies indicated previously with high Na concentration in theses two zones. A dominant [Na] type of environment is favorable to the dissolution and enrichment of fluoride in the form of [NaF]. A similar vertical zoning, i.e., the greater the depth the greater the fluoride content, was found in a discharge zone in northwest China, although this zone was outside the study area (Wang and Cheng 2001). Urbanization has had a profound impact in China since the 1980s, in terms of water demand, wastewater and solid waste discharge. Pollution of air, soil and water related to this process may initially be confined to a local area, but then spread either in a circular pattern from city to suburb or in a linear one following a river passing through the city. Heavy metal/metalloid transport has received much attention since the accumulation of heavy metals in crops is a potential threat to human health through the food web. Current research on heavy metals in China has focused mainly on Cd, Cu, Pb and Zn, and three main sources were identified as industrial emissions, wastewater and solid waste (Cheng 2003). However, Huang and Jin (2008) found that chemical fertilizers and organic manures also contributed to the high contents of Cd, Cu and Zn in the surface soil in the NCP. Extensive vegetable production in the suburbs of large cities, where high rates of chemical fertilizers and organic manures are used, remains

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Major substances such as carbon, nitrogen, and phosphorus had well-integrated cycles and transformations. Groundwater flow and chemical and isotopic contents in the groundwater can be used to trace and identify environmental changes induced either by natural or human processes, the latter of which has became significant since the eighteenth century. Since the half-lives of 3H and 14C are 12.43 and 5730 years, the preferred range for identifying groundwater age is thus 50 and 20–30 ka, respectively. Temperatures during the glacial period of 25–13 ka BP are thought to have been 10°C lower than those at present, and the coastline was 1,000 km east of the current coast (Zhang and Li 2005). These changes can be traced by analyzing the ‘‘messages’’ found in groundwater. Geochemical, geophysical, and biological changes of groundwater also provide evidence of environmental issues such as changes in precipitation and contamination of groundwater over the last 50 years. As shown here, the vertical layers of the NCP reflected natural environmental changes,

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Groundwater age, year Ka BP 0

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O, per mil

Groundwater as a tracer of environmental changes

as well as nitrate pollution and water drawdown associated with human activities. Isotopic features of 18O, deuterium, 3H, and 14C have been used to identify the groundwater age, continental effect, and layering or stratification in the NCP and northwestern China (Chen (ZY) et al. 2002, 2003; Chen et al. 2004b). The layers provide information on paleoclimatic changes in the Holocene and the last glacial period of the Pleistocene (Chen et al. 1998; Yao 1995). Published isotopic 18O and 14C data from the NCP were collected and combined to examine change in 18O with time, which was calculated using 14C (Fig. 6). Temporal data were sorted chronologically, and five data series were averaged, yielding a smooth curve. The d18O value fluctuated in the last 35 ka, with an obvious increase since 10 ka BP reflecting significant environmental change in the NCP. All the changes shown in Fig. 6 were confirmed by other types of evidence, including that provided by pollen, seawater level change, and lake sediment (Yi et al. 2002; Wang et al. 2004; Chen et al. 1998). The isotopic features suggest environmental changes from cold and wet to warm and dry conditions and can help us understand the processes and related issues that have affected the NCP. On the other hand, the layering or vertical stratification indicates that groundwater having a 14C age of less than 10 ka occurs in the UL, while that older than 10 ka years is found in deep layers exceeding depths of 100–150 m. It is thought that the deep aquifer layer was unconfined or semiconfined 30 ka BP and formed as the thickness increased with sedimentation on the subsidence plain (Chen (ZY) et al. 2002). Ren (2006) estimated a sedimentation rate of 0.51–2.67 mm/a for the NCP in the last 40 ka BP, with a weighted average of 1.342 mm/a. Dai et al. (2007) gave a comparatively stable sedimentary rate of 3 mm/a before the 1980s based on the survey in Jiaozhou Bay (close to Qingdao). The increase of sedimentation thickness in the

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significant concern in terms of potential risk of nitrate leaching to the groundwater and heavy metal accumulation in vegetables. Wastewater irrigation and land application of sewage sludge in northern China have been popular practice due to water scarcity in this area, and a high content of Cd with a maximum of 10.15 mg/kg was found in the soil of a suburb in Shenyang after 30 years of sewage irrigation (Wang et al. 2008; Sun et al. 2006). Surface water bodies, i.e., rivers, lakes and reservoirs, are easily polluted by the disposal of non-treated wastewater from cities and mining areas (Yang et al. 2008). A high concentration of As was found in the water of Baiyangdian Lake and, although Hg concentrations were low in the water, levels above the critical threshold level were found in fish due to trophic transfer (Chen et al. 2008). Though heavy metals were found to have accumulated more in the unsaturated zone and surface water bodies than the aquifer, the potential hazard of heavy metals/metalloids in groundwater could not be neglected due to the interactions of surface water/groundwater and saturated/unsaturated zone, and the regional groundwater flow. Attention should be paid not only to the accumulation of heavy metals in the food web but also to its potential occurrence in groundwater even though little research has focused on this aspect. Numerous cases have recently been reported in the Chinese media about Pb poisoning of children in mining areas, where groundwater has been polluted by heavy metals. Phytoremediation and microbial remediation have been suggested to be a promising technique to ease heavy metal pollution (Ye and Zhang 2005; Cheng 2003).

Environ Earth Sci (2010) 61:1037–1047

-10

-11

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Fig. 6 Change of d18O with time, defined by 14C. Data sources: Chen (ZY) et al. (1998, 2002, 2003), Yao (1995), and Shimada et al. (2002)

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last 40 ka can thus be simply approximated as 50–120 m, which is less than or close to the depth between the UL and LL. Therefore, that the formation of groundwater in the aquifer to a depth of 400–500 m in the NCP is generally less than that 30 ka ago cannot be explained simply as a result of the sedimentation process. The groundwater flow system of recharge in the Taihang Mountains and discharge to the Bohai Sea could help clarify the age problem; i.e., older groundwater of more than 30 ka could have been flushed to the Bohai Sea through a flow route having a curved shape and horizontal length of approximately 300 km. The groundwater flow rate in the last 30 ka can thus be roughly calculated at least as 10 m/a. Chemical fertilizer in the NCP has been widely used since the 1980s to increase crop yield. Correspondingly, nitrate groundwater pollution has resulted from overapplication of N-fertilizer and leakage into the aquifer (Zhang et al. 1996). Tritium data were used to identify occurrences of nitrate pollution in the groundwater, as shown in Fig. 7. Figure 7 also illustrates the increasing trend of nitrate concentration with time. Vertical profiles of heavy metals in the core sediment dated by 210Pb chronology were used to identify the environmental changes by human activities, and the case study in the Jiaozhou Bay indicated that three stages could be identified: low sedimentation rate with weak heavy metal pollution and scarce eutrophication before the 1980s, high sedimentation rate and heavy metals and the frequent occurrence of red tide during the period from the 1980s to 2000 with a accelerating pace in the 1990s, and the period after 2000, with improvement to the quality of the environment (Dai et al. 2007). This pattern matches with changes in the economic development of China where, particularly in the 1990s when the economy was spurred by the visit of Deng Xiaoping to southern provinces and his appeal to further reforms in 1992, the economy experienced rapid growths expansion.

Uses of nitrate and heavy metals in the groundwater/ soil/core sediment could be made to investigate both the pollution to human health and the environmental changes due to human activities.

Solutions to water shortage in the NCP As calculated above, the water demand in the NCP is approximately 3.11 9 1010 m3, which could be balanced with recharged water and diversion of Yellow River water. Given that diverted river water could be used fairly and efficiently in the entire NCP without administrative barriers, agriculture depending on groundwater for irrigation could be sustainable as long as no drying-up problems occur in the LYR. Therefore, the South-to-North-Transfer Project (SNTP), by which water from the Yangtze River is to be diverted to the NCP, would be significant only in extreme drought conditions in the NCP and for helping recover the water table and solving the water table depression problem. The probability of the SNTP providing water for agriculture is set at approximately 3 out of 4 years; in other words, 1 year out of 4 without irrigation water is acceptable. The implication that the SNTP will solve water shortages and environmental problems remains arguable, as do the costs of transferring Yangtze River water. Fallow farming practices in the NCP could be another option to solve the drawdown of the water table, although the world market is very sensitive to crop production in China. Subsidies to farmers and efficient uses of stored crops could help save water in the NCP. Water use efficiency in the NCP is rather high compared to that in main crop production areas in countries such as France and the US, and the technical aspects of saving water continue to be discussed.

Conclusions Nitrate concentration in mg/l

160 140 120 100 80 60 40 20 0

0

5

10

15

20

25

30

35

40

45

Tritium in TU Fig. 7 Nitrate concentration related to tritium and its trend curves in the recharge zone. Adapted from Chen (2003)

Water balance components were evaluated in the NCP regarding precipitation, evaporation, flow discharge, and groundwater recharge and discharge, showing a decrease trend in both precipitation and potential evaporation since the 1970s. Actual evaporation was calculated using Kc factor, and annual average water deficit was thus estimated to be 238 mm, which was supplied either by groundwater withdrawal in Hebei Plain including Tianjin and Beijing or water diversion from the Yellow River in the lower reach covering northern part of Shandong Province and Henan Province. Groundwater resource was re-assessed by calculating the recharge in the upper and lower aquifer, yielding a total recharge of 1.65 9 1010 m3/a, while the

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groundwater subtraction for agricultural, industrial and domestic use was estimated to be 3.11 9 1010 m3/a, causing annual average water table drawdown of 0.5 m. Salt accumulation in the unsaturated zone and high chloride content in the groundwater of the discharge zone affected the sustenance of agriculture, and nitrate pollution and high content of fluoride in the aquifer would cause environmental and health problems. The high content of heavy metals in the soil and surface water bodies in suburbs of large cities and mining areas from both point and linear sources are potential threats to human health via impacts on the food web. Regional groundwater resources could also be polluted by heavy metals due to the interaction of surface water/groundwater and the saturated/ unsaturated zone, and care should be taken to protect this valuable resource in the NCP though little research has been carried out. Isotopic data were used to verify the environmental change in the last 35 ka and the groundwater flow rate, indicating an obvious increase of temperature since 10 ka BP and a horizontal flow rate of approximately 10 m/a. Changes of nitrate in groundwater and heavy metals in the core sediment were used to identify recent environmental change induced by human activities, i.e., over use of chemical fertilizers, eutrophication, and industrial development. Fallow farming, water saving practice, and efficient use of diverted water should be adopted with priority to the transfer project from the Yangtze River to deal with water scarcity. Use of chemical fertilizers should be controlled to reduce the accumulation of heavy metals in the soil and crops as well as nitrate in the groundwater. Phytoremediation and microbial remediation are promising techniques to ameliorate environmental degradation in the NCP while further research regarding the mechanisms of remediation is necessary. Acknowledgments This study was supported by the National Natural Science Foundation of China (grant no. 40571027), the Natural Science Foundation of Guangdong Province (grant no. 9251027501000021) and Innovation and Application Research Fund from Water Sciences Department of Guangdong Province (2009– 2011). Thanks are expressed to the anonymous reviewers, Mr James Kirkham of CSIRO Land and Water, and Mr Philip Fountain of Australian National University for improvements to an earlier draft of this paper.

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