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GEOGRAPHICAL RESEARCH >

2017 , Vol. 36 >Issue 2: 361 - 372

DOI: https://doi.org/10.11821/dlyj201702013

Articles

Characterizing the hydrogen and oxygen isotopic compositions of different waters at reclaimed water irrigated district in southeast suburb of Beijing

  • WANG Yajun , 1, 2, 3 ,
  • SONG Xianfang , 1, 2 ,
  • MA Ying 1 ,
  • ZHANG Yinghua 1 ,
  • ZHENG Fandong 4 ,
  • YANG Lihu 1 ,
  • BU Hongmei 1
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  • 1. Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Beijing 100101, China
  • 2. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. Sino-Danish College, University of Chinese Academy of Sciences, Beijing 100190, China
  • 4. Beijing Water Science & Technology Institute, Beijing 100048, China

Received date: 2016-09-07

  Request revised date: 2016-12-03

  Online published: 2017-02-20

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《地理研究》编辑部
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Abstract

Characteristics of hydrogen and oxygen isotope of reclaimed water, surface water and groundwater are essential to recognize hydraulic connection and regional hydrologic cycle. In order to obtain stable isotope (δ18O, δD) characteristics and detect causes of differences among different water bodies (precipitation, reclaimed water, surface water and groundwater in different depths), field investigation and water samples collection were conducted separately in 2014 and 2015 at reclaimed water irrigation district located in the southeast suburb of Beijing. The results showed that: local meteoric water line of Beijing was expressed with the function of δD=7.27 δ18O+2.43 (R2=0.93,n=198) which was well used as isotopic baseline. δ18O value in reclaimed water ranged from -7.4‰ to -6.4‰ and δD ranged from -56‰ to -52‰. Isotopic composition of surface water ranged from -8.2‰ to -4.8‰ in δ18O and from -64‰ to -49‰ in δD. As for groundwater, the wide range in δ18O varied from -13.2‰ to -6‰ and δD ranged from -92‰ to -52‰ respectively. Reclaimed water and surface water carried heavier isotope composition than groundwater, with a descending order of surface water > reclaimed water > groundwater in δ18O and reclaimed water > surface water > groundwater in δD. After the fresh water being used and treated, reclaimed water was enriched in heavy hydrogen and oxygen isotope due to evaporation fractionation. Generally, the heavy isotope becomes enriched gradually along the river flow, while the sudden drop phenomena could be ascribed to entrance of depleted isotope groundwater. On account of slow circulating, the wetland water recharged by the Hanhe River had undergone strongest evaporation which was heaviest isotopic concentration in all the samples. Generally, the isotopic composition of deep groundwater (depth >80 m) was much more depleted than that of shallow groundwater (depth <80 m). The most depleted isotopic value of groundwater at depths of 300 m and 150 m are recharged by the infiltration of precipitation that occurred in colder paleoclimate rather than in modern climate, and no influence occured from reclaimed water. Shallow groundwater from monitoring wells which are located 10 m away from the waterways was dramatically recharged by river and canal water nearby, however lateral flow of depleted groundwater penetrating to some wells adjacent river channel was observed. It is indicated that vertical infiltration of reclaimed water, precipitation and irrigation water with groundwater play vital roles in shallow groundwater recharge at reclaimed water irrigation district.

Key words： reclaimed water irrigation district; hydrogen and oxygen stable isotope; surface water; groundwater; Beijing

Cite this article

WANG Yajun , SONG Xianfang , MA Ying , ZHANG Yinghua , ZHENG Fandong , YANG Lihu , BU Hongmei . Characterizing the hydrogen and oxygen isotopic compositions of different waters at reclaimed water irrigated district in southeast suburb of Beijing[J]. GEOGRAPHICAL RESEARCH, 2017 , 36(2) : 361 -372 . DOI: 10.11821/dlyj201702013

1 引言

再生水资源回用以其成本的降低、土壤质量的改善、向水环境排放污染物的减少等环境经济效益[1-4],成为缓解农业水资源短缺问题的重要途径。北京市再生水通过农业灌溉和河道补给,参与到当地水循环过程,成为水资源重要的组成部分。但再生水的使用存在潜在的危害,如作物品质下降、地下水水质污染甚至对公众健康造成威胁[5]。再生水灌区内水体作为各类污染物的主要载体,水体运移和转化研究显得尤为重要,其中不同水体氢氧同位素特征及特征差异成为研究水体运移和转化过程的基础工作,可为地区水文循环研究提供基本的认识。
氢氧稳定同位素作为环境同位素示踪剂,广泛应用于再生水灌区内不同水体同位素特征和成因的研究。如：Kass等通过分析不同区域井水的氢氧同位素特征,得出灌溉区边缘处的地下水可能受到蒸发的降水补给,或者由同位素富集的Galilee海水补给[6];Bajjali等通过约旦东北部Khirbet Al-Samra污水处理厂附近的地下水、降水和污水处理厂出水氢氧同位素特征,得出污水处理厂上下游浅层地下水的来源[7];Chen等通过研究石家庄污水灌区氢氧同位素关系得出,地下水是伴随有蒸发过程的古地下水和污水的混合水,并计算了污水补给地下水的贡献率[4]。就北京地区而言,再生水灌区内水体的研究大多集中在重金属、有机化合物和微生物等再生水污染方面[8-12],关于不同水体相互转化的研究主要基于整个北京平原区[13,14]、永定河流域[15,16]和潮白河流域[17-19]。因此,在当地大气降水线和区域水文地质条件的基础上,以灌区内再生水、地表水、浅层和深层地下水氢氧同位素特征为切入点,分析灌区内不同水体的氢氧同位素组成和成因,为研究不同水体的运移和相互转化关系提供基本认识,为合理利用再生水资源提供理论基础。

2 研究区概况

北京市东南郊再生水灌区是中国最大的再生水灌区之一,隶属于大兴区和通州区,覆盖面积为789 km2,39°35′N~39°52′N,116°23′E~116°53′E（图1a）。该区属于暖温带半干旱半湿润大陆性季风气候,夏季炎热多雨,冬季寒冷干燥,年平均气温为12 ℃,多年（1951-2010年）平均降水量为580 mm,主要集中在6-9月,多年平均潜在蒸发量为1800 mm[20]。研究区为典型农业种植区[21],农业面积占到研究区总面积的58.9%。区内河渠密布,主要河流为萧太后河、新凤河、凉水河、凤港减河、旱河、岔河和凤河,其中萧太后河和新凤河最终汇入凉水河,旱河和岔河汇入凤河,凤港减河汇入北运河。
Fig.1 The geographic location map of the study area (a) and hydrogeologic section map (b)[22]

图1 研究区位置图（a）及水文地质剖面图（b）[22]

研究区主要受永定河和潮白河第四纪交错沉积的冲洪积扇控制,地形平坦,地势由西北向东南缓慢倾斜,第四纪覆被厚度由西北向东南逐渐增加。含水层系统为砂砾石和黏性土交替分布的多层含水层,水位埋深为3~24 m（图1b）。地下水系统补给来源主要包括降水入渗、河道入渗、农业灌溉水入渗、地下水侧向补给等,排泄方式包括人工开采、侧向流、蒸发和植物吸收等[23]。
灌区主要分为南红门灌区和新河灌区（图1a）。南红门灌区再生水源主要来自小红门污水处理厂（XHM）和黄村（HC）污水处理厂出水。小红门污水处理厂出水经凉凤灌渠、北野厂灌渠进入灌区,黄村污水处理厂出水经新凤河、北野厂灌渠进入南红门灌区。南红门灌区内的主要河渠包括北野支渠、旱河、岔河、凤河。新河灌区再生水源主要来自高碑店污水处理厂（GBD）出水,经通惠北干渠进入凉水河后,通过分水闸进入马驹桥干渠以及下游的胜利干渠。凉水河再生水经通惠南干渠进入凤港减河,进而分水给胜利干渠和红旗渠干渠。新河灌区内的主要河渠包括通惠北干渠、马驹桥干渠、胜利干渠、凤港减河、红旗渠干渠和东风干渠。

3 研究方法与数据来源

3.1 样品采集

为了研究灌区内不同水体的氢氧同位素特征,分别于2014年10月和2015年9月采集了灌区内再生水（污水处理厂出水）、地表水（河水、渠道水和湿地水）和地下水水样,其中2014年包括3个再生水水样、13个地表水样和27个地下水样,2015年包括3个再生水水样、21个地表水样和25个地下水水样,TZS/G和DXS/G分别表示通州区和大兴区所属的地表水和地下水,具体采样点见图2。降水水样来自北京市中国科学院地理科学与资源研究所地理科学馆楼顶（40°00′11″N,116°23′7″E,海拔高度为45 m,距离地面高度为10 m）2006-2015年收集的198次降水事件（>5 mm）。在楼顶开阔处,雨水通过一个装有漏斗的1000 ml的聚乙烯瓶子收集,降雪则通过一个圆桶收集并于室温融化,每次降水事件后立即将水样转移到50 ml的塑料瓶中,用胶带密封并低于4 ℃保存。再生水分别于高碑店污水处理厂、小红门污水处理厂和黄村污水处理厂的二级出水口采集,YGZ湿地水为杨各庄湿地公园的地表水。2014年地下水主要采自距离河道10 m范围内的监测井,大部分井深小于80 m,其中FHY20、FHY40和FHY60为凤河营同一位置三口井,井深分别为20 m、40 m和60 m,YGZ20、YGZ40和YGZ60同上,位于杨各庄湿地公园内。2015年地下水主要采自农田灌溉机井。通过水文地质条件、地下水的地球化学和同位素组成将华北平原分为浅层和深层的地下水系统,且其分界线在80~100 m深度[15,24]。因此选取80 m深度作为深层和浅层地下水分界线。
Fig.2 The sampling sites distribution map

图2 采样点分布图

3.2 样品测试

水样的氢氧同位素组成在中国科学院地理科学与资源研究所陆地水循环及地表过程重点实验室进行测定,测定仪器为液态水同位素分析仪（LGR-DLT100,USA）,测定结果以相对维也纳标准平均海水（VSMOW）的千分差表示,测定精度分别为±1‰（δD）和±0.1‰（δ18O）。大气降水氘盈余值（d-excess）作为反映远距离水汽来源的气候条件信息的指标,与湿度负相关[25,26],其计算公式为：
d=δD-8δ18O （1）
不同水体同位素蒸发效应的强烈程度通常也用氘盈余来描述[27]。使用IBM SPSS Statistics 21中比较均值的样本T检验方法对不同年份和不同水体的氢氧同位素数据作显著性分析。

4 结果分析

4.1 降水氢氧同位素特征

降水作为陆地水循环过程的主要输入项,其携带的初始同位素信号对于研究地表水、地下水中环境同位素组分分布及变化具有重要的指示意义。由降水同位素确定的当地大气降水线（LMWL）,可以为当地水文、气象和水文地质研究提供地区性基准。采用2006-2015年中国科学院地理科学与资源研究所地理科学馆楼顶收集的次降水（>5 mm）氢氧同位素数据（图3）,拟合得到北京市平原区大气降水线：
δD=7.27δ18O+2.43（R2=0.93,n=198） （2）
式中：δD为氢同位素实测比值;δ18O为氧同位素实测比值。本文主要分析2014年和2015年6-10月的降水同位素数据。2014年6-10月降水δD和δ18O的均值分别为-40‰和-5.4‰,2015年6-10月降水δD和δ18O的均值分别为-47‰和-6.6‰。2014年6-10月降水氢氧同位素大于2015年同期值,但不显著,氘盈余平均值小于2015年（表1）。
Fig.3 The local meteoric water line of study area

图3 研究区当地大气降水线

Tab. 1 Statistic characteristic of different water bodies in reclaimed water irrigation region(‰)

表1 再生水灌区内不同水体同位素统计特征（‰）

指标 最大值 最小值 均值 标准差 比较均值t检验
年份 2014年 2015年 2014年 2015年 2014年 2015年 2014年 2015年 t值 Sig.
降水 δD -7 2 -64 -77 -40 -47 24.0 24.9 0.637 0.541
δ18O 0.4 0.0 -9.0 -10.3 -5.4 -6.6 4.0 2.7 0.535 0.604
氘盈余 13.8 11.1 -10.5 1.4 3.7 5.2 8.7 2.7 - -
再生水 δD -52 -52 -56 -54 -54 -53 2 1 -0.786 0.491
δ18O -6.4 -6.9 -7.4 -7.3 -6.9 -7.1 0.4 0.2 0.081 0.487
氘盈余 3.2 4.8 -0.4 3.2 0.9 3.9 1.6 0.7 - -
地表水 δD -49 -50 -55 -64 -53 -55 2 3 2.519 0.017
δ18O -4.8 -6.4 -7.4 -8.2 -6.2 -7.1 0.7 0.4 3.905 0.001
氘盈余 4.7 4.6 -10.6 0.0 -2.9 2.0 5.0 1.3 - -
地下水 δD -52 -56 -76 -92 -59 -70 6 10 4.501 0.000
δ18O -6.0 -6.9 -9.6 -13.2 -7.7 -9.2 0.9 1.6 3.945 0.000
氘盈余 14.8 13.4 -8.2 -4.5 2.8 3.8 5.2 3.9 - -

注：-表示未作分析（氘盈余由δD和δ18O计算而得,未作分析）。

4.2 再生水氢氧同位素特征

高碑店污水处理厂、小红门污水处理厂和黄村污水处理厂主要接纳周边城镇生活污水和工业废水,经二级处理后作为再生水排入河渠中。2014年与2015年的再生水氢氧同位素在比较均值t检验中显著性（Sig.）均大于0.05,表明两年再生水氢氧同位素无显著差异。6个再生水水样中,δD值变动范围为-56‰~-52‰,δ18O值变动范围为-7.4‰~-6.4‰（表1）,均值分别为-54‰和-7.0‰。

4.3 地表水氢氧同位素特征

地表水的氢氧同位素特征反映了地表特征、气候条件和水文过程等。地表水采集自河渠水和湿地水,其中河渠水主要由污水处理厂出水（再生水）排入,沿河道和灌渠自西北向东和向南流动,湿地水采自杨各庄湿地水体（YZG）。地表水整体的δD值变化范围为-64‰~-49‰,δ18O值变化范围为-8.2‰~-4.8‰,均值分别为-54‰和-6.8‰,与再生水氢氧同位素均值大致相同,氘盈余值集中分布在1‰~5‰,个别水样点TZS04'、DXS04'和DXS03'的氢氧同位素偏低。2014年采集的地表水氢氧同位素均值显著大于2015年,而2014年氘盈余值小于2015年（表1、图4）。YGZ湿地水氢氧同位素组成分别为-49‰和-4.8‰,同位素最为富集。
Fig.4 Scatter diagram of δD and δ18O in surface water

图4 地表水氢氧同位素散点图

2015年南红门灌区的旱河、岔河和新河灌区的凉水河同位素组成的沿程变化特征,如图5所示。以高碑店污水处理厂出水口为起始点,沿着凉水河流程,δ18O值和δD值变化趋势一致。在TZS03'点同位素组分最低,之后沿程同位素组分逐渐升高。旱河和岔河由西向东汇入凤河,与当地地下水流向一致,主要接纳黄村和小红门再生水,以凉凤灌渠和新凤河交汇点为起始点,旱河同位素组分在点DXS03'突然降低,随着流程增长,河水同位素值不断升高。岔河沿程氢氧同位素波动平缓,δ18O值变动幅度大于δD值,由氧同位素和氘同位素分馏程度不同引起,沿着河流流向,氢氧同位素未呈现出重同位素累积的现象。
Fig.5 Variations of δD and δ18O compositions in different rivers along flow direction

图5 不同河流氢氧同位素沿程变化

4.4 地下水氢氧同位素特征

2014年采集地下水δD和δ18O均值分别为-59‰和-7.7‰,2015年分别为-70‰和 -9.2‰,2014年地下水氢氧同位素显著大于2015年（表1）。地下水的同位素分布范围较广,有明显的聚集分区,主要分为深层地下水（区域A）、混合水（区域B）和浅层地下水（区域C）（图6）。
Fig.6 Relationship diagram of isotopic composition in different water bodies

图6 不同水体氢氧同位素关系图

4.4.1 深层地下水氢氧同位素特征
DXG08'点（井深300 m）氢氧同位素值最为贫化（δD为-92‰,δ18O为-13.2‰）,分布于图中左下角。氢氧同位素贫化的水样点除DXG08'点外,还包括DXG09'、DXG12'、DXG11'、TZG09'和TZG01'（区域A）,该区域δD变化范围为-89‰~-79‰,δ18O变化范围为-12.0‰~-10.0‰,均值分别为-85‰和-11.4‰,区域A中深层地下水氢氧同位素显著小于浅层地下水氢氧同位素。
4.4.2 浅层地下水氢氧同位素特征
区域C内浅层地下水水样点δD变化范围为-64‰~-52‰,δ18O变化范围为-9.1‰~ -6.0‰,均值分别为-58‰和-7.6‰。在图6中与地表水混合分布,氘盈余值分布在0‰~5‰之间,与地表水氘盈余分布一致。区域B内的水样点（DXG01'、DXG02'、DXG03'、DXG04'、DXG05'、DXG06'、DXG07'、TZG08'、TZG10'、TZG01、TZG14、TZG15、FHY60）δD变化范围为-73‰~-66‰,δ18O变化范围为-9.8‰~-8.5‰,均值分别为-70‰和-9.4‰,分布于当地降水线以下,介于区域C和区域A之间。
选取了距离1 km范围内相邻的监测井和灌溉井浅层地下水样点,比较二者氢氧同位素的分布特征（表2）。河道监测井水的氢同位素均值显著高于灌溉井水,除了TZG07点外,河道监测井水的氧同位素值大于灌溉井,氘盈余无明显特征。表明河道监测井水（地下水）氢氧同位素相对于灌溉井水（地下水）更为富集。
Tab. 2 Comparison of isotopic compositions in adjacent shallow groundwater(‰)

表2 相邻浅层地下水氢氧同位素特征对比（‰）

河道监测井 δD δ18O 氘盈余 灌溉井 δD δ18O 氘盈余
TZG03 -59 -7.4 0.4 TZG01' -79 -10.2 2.9
TZG04 -58 -8.5 9.8 TZG04' -72 -9.8 6.1
TZG07 -58 -9.1 14.8 TZG07' -62 -8.3 4.7
TZG05 -54 -7.3 3.9 TZG03' -63 -7.9 0.6
TZG11 -52 -6.0 -3.7 TZG13' -56 -7.2 1.7
DXG02 -64 -7.9 -0.1 DXG03' -68 -8.5 0.3
DXG07 -55 -7.4 3.7 DXG09' -89 -12.0 7.7
DXG05 -54 -7.7 7.3 DXG07' -71 -9.8 6.9
FH20-40-80（平均） -62 -8.0 2.2 DXG08' -92 -13.2 13.4

5 讨论

本文使用多年实测的降水氢氧同位素数据得到北京平原区大气降水线为δD=7.27 δ18O+2.43（R2=0.93,n=198）,与卫克勤等[28]的北京地区1979年、1980年降水线δD=7.3δ18O+7.9基本一致,斜率略大于Zhai等[29]根据2008年7月至2009年7月降水数据得到的大气降水线δD=7.0181δ18O+3.5231（R2=0.86,n=36）的斜率,而小于Liu等[30]通过2005-2010年降水氢氧同位素月均值拟合得到的北京大气降水线（δD=7.94δ18O+3.92）斜率。但Liu等的降水收集点海拔高度为1248 m,不能代表北京平原区。通过与其他学者研究结果比较可知,本文得到的北京大气降水线能够为本文研究提供基准值,从而能够进一步地分析再生水、地表水和地下水的同位素特征及成因。

5.1 再生水和地表水氢氧同位素成因

通过图4中氢氧同位素散点图,可以看出,再生水同位素分布于当地大气降水线以下,图6的右上部。再生水最初来源于人类用水,而人类用水主要来自氢氧同位素贫化的地下水,在经历使用、混合和污水处理等过程中,不断地蒸发作用使得再生水氢氧同位素富集。
地表水整体氢氧同位素关系方程为δD=3.09δ18O-33.17（R2=0.51,n=34）,斜率低于当地大气降水线斜率,是强烈蒸发分馏作用的结果。2014年地表水氢氧同位素大于2015年,但作为主要补给源的再生水氢氧同位素在2014年和2015年没有显著差异,考虑到2014年降水同位素大于2015年（表1）,地表水同位素2014年和2015年差异的原因可能是降水补给的影响,再者,2015年部分地表水采样点（TZS04'、DXS04'和DXS03'）氢氧同位素值远小于再生水和降水,因此也可能是2015年的地表水存在氢氧同位素贫化水体的输入。再生水排入河渠后,不断受到蒸发分馏作用,河渠水的氢氧同位素值沿河流流向应该不断增大,然而凉水河的TZS03'和旱河的DXS03'氢氧同位素突然降低,之后沿着河流方向,同位素不断升高。在TZS03'处和DXS03'处上游两岸分别为农田和蔬菜大棚,且主要抽取地下水用于灌溉。因此,河渠水同位素在TZS03'和DXS03'处骤然降低的原因可能是抽取的地下水从地表流入或下渗地下水侧向流入河道。YGZ湿地水引自旱河,主要由再生水补给,水体更新缓慢,受到长期的蒸发作用,同位素最为富集。

5.2 地下水氢氧同位素成因

2014年地下水氢氧同位素显著大于2015年（表1）,主要是两年采集水井类型不同造成的,其中2015年采集多口深水井使得地下水氢氧同位素均值更为贫化。
5.2.1 深层地下水氢氧同位素成因
深层地下水DXG08'点（井深300 m）位于研究区地下水流向末端,连续多层黏土层使得该区域地下水脆弱性指数最低[31]。且该点氢氧同位素最为贫化,位于当地大气降水线以上,说明寒冷气候条件下的大气降水为该处地下水主要补给来源（图6）,不会受到浅层地下水和地表水下渗影响。区域A位于当地大气降水线以下,氢氧同位素贫化（δD：-89‰~-79‰,δ18O：-12.0‰~-10.0‰）,显著区别于其他地下水样点的氢氧同位素,属于古地下水,来自寒冷气候下降水入渗补给。这与Chen等关于华北平原中部深层地下水来源于末次冰期的降水补给结果[32]一致。研究区深层地下水属于区域性地下水流动系统[33],主要来源于侧向补给[15],未受到再生水影响。
5.2.2 浅层地下水氢氧同位素成因
图6中,区域B内的水样点分布于氢氧同位素关系图的中间区域,位于现代水（区域C）和深层地下水（区域A）之间,属于二者的混合水。通过比较均值T检验,区域B与区域C的氢氧同位素均值具有显著性差异。区域B地下水主要由来自西部侧向流入的古地下水[16]、地表水和降水共同补给。
区域C内浅层地下水样点（包括河道监测井水样）位于大气降水线附近,其最初来源于大气降水。区域C内地下水与地表水、再生水混合分布,其氘盈余与地表水氘盈余分布一致,二者整体上有相似的水汽来源,表明浅层地下水和地表水之间存在水力联系,由降水和地表水（河渠水、用于灌溉的再生水或用于灌溉的地下水）共同补给。垂直入渗是研究区浅层地下水补给的主导过程,灌溉水（再生水和抽取的地下水）影响不容忽视[34]。同时区域C地下水同位素与华北平原现代地下水（年龄<40年）的氧同位素变化范围（-9.0‰~-6.0‰）[32]一致,证实了研究区浅层地下水为现代水补给。
河道监测井毗邻河道,其地下水氢氧同位素在图6中分布于河渠水附近,说明河道附近浅层地下水与河渠水水力联系紧密[35]。距离1 km外的灌溉井地下水氢氧同位素显著贫化于河道监测井（δD：t=4.039,Sig.=0.004;δ18O：t=3.011,Sig.=0.017）,表明1 km外的浅层地下水受到河渠水侧向补给作用小。位于B区域（混合水）的河道监测井水的同位素值小于河渠水,表明这几个河道监测井地下水除了受到河道水的入渗外,贫化的地下水也具有重要的补给作用。

6 结论

通过2006-2015年中国科学院地理科学与资源研究所地理科学馆楼顶多年降水氢氧同位素数据得到北京市平原区大气降水线方程为：δD=7.27 δ18O+2.43（R2=0.93,n=198）,为本文提供地区性基准。再生水灌区内2014年与2015年的再生水氢氧同位素无显著差异,δD值变化范围为-56‰~-52‰,δ18O值变化范围为-7.4‰~-6.4‰,均值分别为-54‰和-7.0‰。2014年的地表水氢氧同位素大于2015年,可能为降水影响,也可能是由于2015年地表水存在贫化地下水的输入,δ18O值为-8.2‰~-4.8‰,δD值为-64‰~-49‰,均值分别为-54‰和-6.8‰。再生水经过人类使用、混合及处理过程,氢氧同位素富集。河渠水主要是由污水处理厂出水（再生水）补给,部分地点的河渠水受到同位素贫化地下水的混入,之后沿着流程增长,氢氧同位素值不断累积升高。湿地水由旱河水补给,经历长期的蒸发作用,氢氧同位素最为富集。
地下水氢氧同位素变化范围较大,δ18O值变化范围为-13.2‰~-6‰,δD值变化范围为-92‰~-52‰,均值分别为-64‰和-8.4‰。深层地下水氢氧同位素显著地小于浅层地下水,揭示了深层和浅层地下水补径排条件的差别。深层地下水（300 m和150 m左右）氢氧同位素最为贫化,由寒冷气候条件的大气降水入渗补给。深度小于80 m的浅层含水层中,氢氧同位素组分具有不同的特征：分布于现代水和深层地下水之间的混合地下水,由古地下水、再生水和大气降水共同补给;河道监测井水与地表水氢氧同位素集中的分布,二者水力联系紧密,河渠水对其附近浅层地下水具有强烈补给作用,部分地区河道附近的浅层地下水除了受到河渠水补给外,还受到贫化地下水的补给。本文通过分析再生水灌区内再生水、地表水（湿地水和河渠水）和地下水氢氧同位素特征,得出不同水体的氢氧同位素差异性成因,为再生水灌区内不同水体的水力联系提供基本的认识。
致谢：感谢北京市水科学技术研究院李炳华博士参与野外采样工作。

The authors have declared that no competing interests exist.

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[18]
翟远征, 王金生, 周俊. 北京市潮白河冲洪积扇地下水流动和更新模式的水化学和同位素标记. 应用基础与工程科学学报, 2013, 21(1): 32-44.

[Zhai Yuanzheng, Wang Jinsheng, Zhou Jun.Hydrochemical and isotopic markers of flow patterns and renewal mode of groundwater in Chaobai River alluvial fan in Beijing. Journal of Basic Science and Engineering, 2013, 21(1): 32-44.]

[19]
Li J, Liu J, Pang Z, et al.Characteristics of chemistry and stable isotopes in groundwater of the Chaobai River Catchment, Beijing. Procedia Earth and Planetary Science, 2013, 7: 487-490.

[20]
Zhai Y Z, Guo Y L, Zhou J, et al.The spatio-temporal variability of annual precipitation and its local impact factors during 1724-2010 in Beijing, China. Hydrological Processes, 2014, 28(4): 2192-2201.Rapid population growth and increased economic activity impose an urgent challenge on the sustainability of water resources in Beijing. Understanding the spatial and temporal variability of precipitation is of the upmost importance in order to sustain the region's water resources. Two time series, one long term (1724-2010) from a single meteorological station and a shorter time series (1980-2010) from 20 different meteorological stations within the Beijing area, were analysed using Linear Regression, Moving Average, Mann-Kendall, Rescaled Range and Spatial Interpolation methods. Results from both the long- and short-term meteorological data show a mean annual precipitation rate of 600mm and 540mm respectively. Annual precipitation rates have decreased during the 21st century by an estimated 100mm or 16% in comparison to the 1990s. The 1980-2010 data show an increase in precipitation during the early 1990s followed by a sharp decrease during the subsequent years. The change of annual precipitation with time is more random and diverse in comparison to space. The main local impact factors (terrain, urbanization and elevation) and how they work on the local precipitation especially the spatial diversity are identified qualitatively. Generally speaking, (1) the annual precipitation of the plain area is more than that of the mountainous area (terrain effect), (2) the annual precipitation of the urban area in the plain area is obviously more than that of the surrounding suburb area (urbanization effect) and (3) the annual precipitation of the lower location is approximately more than that of the higher location (elevation effect). Copyright (c) 2013 John Wiley & Sons, Ltd.

DOI

[21]
杨雪, 谈明洪. 北京市耕地功能空间差异及其演变. 地理研究, 2014, 33(6): 1106-1119.城市化对耕地及其功能具有深刻影响，这在大都市郊区尤为明显。立足北京市，构建耕地功能评价指标体系，运用极差标准化法处理数据，采用层次分析法确定指标权重，最后运用加权求和法得出功能值。研究表明：① 在北京各区县，2004-2011 年间单位面积耕地的生产、生态、文化和社会功能几乎均增强，空间差异表现为生产和社会功能远郊平原区高于远郊山区和近郊区，生态功能远郊平原区高于远郊山区，文化功能近郊区高于远郊区。② 北京远郊平原区的粮食、蔬菜和瓜类生产功能均较强，但农业污染较严重。受距市中心距离影响，近郊区耕地文化功能需求量较大，远郊区供给量较大。③ 2004-2011 年间绝大部分区县单位面积耕地的总功能增强，受地形和市中心经济辐射影响，远郊平原区高于远郊山区和近郊区。④ 根据耕地总功能组成比重，把北京市耕地分为四种类型：生产型（远郊平原区）、生态型（近郊区）、文化型（丰台区和门头沟区）与社会型（远郊山区）.

DOI

[Yang Xue, Tan Minghong.Spatial differences and evolution of arable land functions in Beijing. Geographical Research, 2014, 33(6): 1160-1119.]

[22]
张兆吉, 费宏宇. 华北平原地下水可持续利用图集. 北京: 中国地图出版, 2009.

[Zhang Zhaoji, Fei Hongyu.Atlas of Groundwater Sustainable Utilization in North China Plain. Beijing: SinoMaps Press, 2009.]

[23]
刘锋, 李延河, 林建. 北京永定河流域地下水氢氧同位素研究及环境意义. 地球学报, 2008, 29(2): 161-166.

[Liu Feng, Li Yanhe, Lin Jian.Hydrogen and oxygen isotope study of groundwater in the Yongding River Drainage of Beijing and its environmental significance. Acta Geoscientica Sinica, 2008, 29(2): 161-166.]

[24]
Chen J Y, Tang C Y, Sakura Y, et al.Spatial geochemical and isotopic characteristics associated with groundwater flow in the North China Plain. Hydrological Processes, 2004, 18(16): 3133-3146.

[25]
Jouzel J, Merlivat L.Deuterium excess in an East Antarctic ice core suggests higher relative humidity at the oceanic surface during the last glacial maximum. Nature, 1982, 299: 688-691.

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Wen X F, Zhang S C, Sun X M, et al.Water vapor and precipitation isotope ratios in Beijing, China. Journal of Geophysical Research: Atmospheres, 2010, 115(D1): D01103.

[27]
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[Shao Yisheng.The evaporation effect of isotope in surface water and the usage to hydrogeology. Geotechnical Investigation & Surveying, 1988, (3): 33-36.]

[28]
卫克勤, 林瑞芬, 王志祥. 北京地区降水中的氘、氧-18、氚含量. 中国科学: B辑. 1982, (8): 754-757.

[Wei Keqin, Lin Ruifen, Wang Zhixiang.Compositon of Deuterium, Oxygen-18 and tritium in precipitation at Beijing. Scientia Sinica: B, 1982, (8): 754-757.]

[29]
Zhai Y Z, Wang J S, Zhang Y, et al. Hydrochemical and isotopic investigation of atmospheric precipitation in Beijing, China. Science of the Total Environment, 2013, 456-457: 202-211.

[30]
Liu J R, Song X F, Yuan G F, et al.Stable isotopic compositions of precipitation in China. Tellus B, 2014, 66.

[31]
Wu W Y, Yin S Y, Liu H L, et al.Groundwater vulnerability assessment and feasibility mapping under reclaimed water irrigation by a modified DRASTIC model. Water Resources Management, 2014, 28(5): 1219-1234.Increasing water shortages promote reclaimed water irrigation (RWI), which potentially causes additional contaminants in groundwater. The DRASTIC model has become an important tool to assess specific groundwater vulnerability. In this study, five parameters of the model were kept to calculated intrinsic vulnerability index (IVI). Aquifer media rating is calculated using the weighted average of ratings for all mediums instead of using the major medium rating, and the rating of the impact of vadose zone is adjusted for the clayey soils on the basis of their thickness. Subsequently, a single parameter sensitivity analysis is used to compute the effective weights of those five parameters. The Pearson's correlation coefficient between IVI and Nemerow's synthetical pollution Index (NI) of groundwater quality is significantly improved from 0.185 to 0.775 after four steps of revision. The RWI factor, R-rr, is introduced to assess specific vulnerability index (SVI) under RWI. The SVI decreases from east to west with the increases in depth to water, clayey soil thickness, and other factors. To manage contamination risk, the study area is divided into preferential zones, feasible zones and unfeasible zones for RWI planning and operation with suggested engineering measures.

DOI

[32]
Chen Z Y, Qi J X, Xu J M, et al.Paleoclimatic interpretation of the past 30 ka from isotopic studies of the deep confined aquifer of the North China plain. Applied Geochemistry, 2003, 18(7): 997-1009.The <em>δ</em><sup>18</sup>O and <em>δD</em> values in the deep confined aquifer beneath the North China Plain which is located at 112&deg;30&prime;E&ndash;119&deg;30&prime;E and 34&deg;46&prime;N&ndash;40&deg;25&prime;N, reflect differences in paleoclimatic conditions between the Holocene and the late Pleistocene. Groundwater samples whose <sup>14</sup>C ages are between 12 and 25 ka B.P have ranges of &minus;9.4 to &minus;11.7&permil; for <em>δ</em><sup>18</sup>O and &minus;76&permil; to &minus;85&permil; for <em>δD</em> values. These very negative <em>δ</em><sup>18</sup>O and <em>δD</em> values reflect the cold and arid climate in the last glacial period. The temperature estimated in this period is 6&ndash;9&nbsp;&deg;C cooler than that of the present. The entire ranges of <em>δ</em><sup>18</sup>O and <em>δD</em> values for samples with <sup>14</sup>C dating from 7 ka B.P to present are &minus;7.7&permil; to &minus;10.2&permil; and &minus;63&permil; to &minus;73&permil; respectively. The greater <em>δ</em><sup>18</sup>O and <em>δD</em> enrichments of these samples indicate a period of relatively humid and warm climate in the Holocene. However, the wide ranges of <em>δ</em><sup>18</sup>O (&minus;9.0&permil; to &minus;11.1&permil;) and <em>δD</em> (&minus;66&permil; to &minus;80&permil;) values for samples with <sup>14</sup>C age ranging from 12 to 7 ka B.P. imply an unstable climatic condition of rapidly increasing temperature, which marks the transition from the Pleistocene to the Holocene.

DOI

[33]
Aji K, Tang C Y, Song X F, et al.Characteristics of chemistry and stable isotopes in groundwater of Chaobai and Yongding River basin, North China Plain. Hydrological Processes, 2008, 22(1): 63-72.

[34]
Rohden C, Kreuzer A, Chen Z, et al.Characterizing the recharge regime of the strongly exploited aquifers of the North China Plain by environmental tracers. Water Resources Research, 2010, 46(5): W05511.

[35]
Yin S Y, Wu W Y, Liu H L, et al.The impact of river infiltration on the chemistry of shallow groundwater in a reclaimed water irrigation area. Journal of Contaminant Hydrology, 2016, 193: 1-9.

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