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Global Isotope Hydrogeology―Review

Wiley
Reviews of Geophysics
Authors:
Scott Jasechko
Scott Jasechko
Scott Jasechko
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Abstract and Figures

Groundwater ¹⁸O/¹⁶O, ²H/¹H, ¹³C/¹²C, ³H, and ¹⁴C data can help quantify molecular movements and chemical reactions governing groundwater recharge, quality, storage, flow, and discharge. Here, commonly applied approaches to isotopic data analysis are reviewed, involving groundwater recharge seasonality, recharge elevations, groundwater ages, paleoclimate conditions, and groundwater discharge. Reviewed works confirm and quantify long held tenets: (i) that recharge derives disproportionately from wet season and winter precipitation; (ii) that modern groundwaters comprise little global groundwater; (iii) that “fossil” (>12,000‐year‐old) groundwaters dominate global aquifer storage; (iv) that fossil groundwaters capture late‐Pleistocene climate conditions; (v) that surface‐borne contaminants are more common in younger groundwaters; and (vi) that groundwater discharges generate substantial streamflow. Groundwater isotope data are disproportionately common to midlatitudes and sedimentary basins equipped for irrigated agriculture, but less plentiful across high latitudes, hyperarid deserts, and equatorial rainforests. Some of these underexplored aquifer systems may be suitable targets for future field testing.
Common hydrogeological interpretations based on groundwater isotope compositions. Each of the circles is reviewed in the forthcoming subsections (see section numbers aside each circle). Circles along the top portion of the figure relate to groundwater recharge (sections 2–4); circles along the left side of the figure relate to the isotope composition of groundwater stored in aquifers and pumped from wells (sections 5–6); and circles on the lower‐right side of the figure depict groundwater discharges (sections 7 and 8).
Common hydrogeological interpretations based on groundwater isotope compositions. Each of the circles is reviewed in the forthcoming subsections (see section numbers aside each circle). Circles along the top portion of the figure relate to groundwater recharge (sections 2–4); circles along the left side of the figure relate to the isotope composition of groundwater stored in aquifers and pumped from wells (sections 5–6); and circles on the lower‐right side of the figure depict groundwater discharges (sections 7 and 8).
… 
Groundwater δ¹⁸O measurements made in spring and well waters around the globe. (a) Groundwater isotope measurement locations and δ¹⁸O values. High δ¹⁸O values are common at low latitudes and near coastlines; low δ¹⁸O values are common at high latitudes, high elevations, and continental interiors. Groundwater isotope data are relatively common throughout the contiguous United States, southern Canada, Europe, north and east Africa, north China, Bangladesh, the western islands of the Malay Archipelago, New Zealand, and populated regions of Australia. Groundwater isotope data are relatively sparse across Latin America, southwest Africa, central Asia, eastern Europe, central and southern China, Borneo, New Guinea, and areas of Australia. For example, relatively high‐density and nation‐wide groundwater δ¹⁸O data sets exist for Ireland (Regan et al., 2017), Costa Rica (Sánchez‐Murillo & Birkel, 2016), Uganda (Jasechko, 2014; samples collected with M. GebreEgziabher), Mexico (Wassenaar et al., 2009), India (Bhattacharya et al., 1985), South Africa (West et al., 2014), the United States of America, and Canada (Jasechko, Wassenaar & Mayer, 2017). (b) Groundwater (grey circles) and annual amount‐weighted precipitation (black squares) δ¹⁸O values and their variance with latitude. Precipitation isotope compositions are derived from the International Atomic Energy Agency (www‐naweb.iaea.org/napc/ih/IHS_resources_isohis.html), the United States Network for Isotopes in Precipitation (Welker, 2012) and the Canadian Network for Isotopes in Precipitation (e.g., Birks & Gibson, 2009; Delavau et al., 2011). Precipitation δ¹⁸O values plotted in panel b are ‘amount‐weighted’ over the entire period of record, meaning time‐steps during which more precipitation fell are weighted more than those during which less precipitation fell. Groundwater δ¹⁸O data presented here are derived from the United States' National Water Information System (data downloaded May 2018 from www.waterqualitydata.us) and from data sets compiled from the following n = 435 references (Al Faitouri & Sanford, 2015; Abid et al., 2010; Abid et al., 2011; Abid et al., 2012; Abouelmagd et al., 2014; Abu‐Jaber & Kharabsheh, 2008; Adams et al., 2001; Adiaffi et al., 2009; Adomako et al., 2011; Aeschbach‐Hertig et al., 2002; Aggarwal et al., 2000; Ahmad & Green, 1986; Ahmed et al., 2011; Ako Ako et al., 2012; Al‐Charideh & Abou‐Zakhem, 2010; Al‐Charideh, 2012; Al‐Charideh & Kattan, 2016; Al‐Charideh & Hasan, 2013; Alemayehu et al., 2011; Al‐Katheeri et al., 2009; Allen, 2003; Al‐Mashaikhi et al., 2012; Alpers & Whittemore, 1990; Al‐Ruwaih & Shehata, 2004; Alsaaran, 2005; Alyamani, 2001; Amer et al., 2012; Andre et al., 2005; Andrews et al., 1989; Andrews, Edmunds, et al., 1994; Andrews, Fontes, et al., 1994; Aravena et al., 2003; Arslan et al., 2013; Atkinson et al., 2014; Awad, 2011; Awad et al., 1994; Awad et al., 1997; Awad, 1997; Back et al., 1983; Bahati et al., 2005; Bajjali & Abu‐Jaber, 2001; Bajjali, 2006; Bakari, Aagaard, Vogt, Ruden, Brennwald, et al., 2012; Baker, 2009; Barbecot et al., 2000; Batista, Santiago, Frischkorn, Filho, & Forster, 1998; Bayari et al., 2009; Bennetts et al., 2006; Berg & Pearson, 2012; Beyerle et al., 1998; Beyerle et al., 2003; Bhatia et al., 2011; Bhattacharya et al., 1985; Blomqvist, 1999; Böhlke et al., 1998; Bouchaou et al., 2008; Bouchaou et al., 2009; Bouragba et al., 2011; Boutin, 2009; Bowen et al., 2012; Branchu & Bergonzini, 2004; Bretzler et al., 2011; Brown et al., 2011; Buck et al., 2005; Burg et al., 2013; Bwire Ojiambo et al., 2001; Calmels et al., 2008; Capaccioni et al., 2003; Carneiro et al., 1998; Carreira et al., 2011; Carreira, Marques & Nunes, 2014; Carrillo‐Rivera et al., 1992; Cartwright et al., 2012; Cartwight & Morgenstern, 2012; Cartwright & Weaver, 2005; Castany et al., 1974; Celle‐Jeanton et al., 2009; Cheikh et al., 2012; Chen et al., 2003; Chen et al., 2005; Chen et al., 2011; Chen et al., 2012; Chen et al., 2014; Cheung & Mayer, 2009; Choi et al., 2005; Ciezkowski et al., 1992; Cidu & Bahaj, 2000; Clark et al., 1987; Clark et al., 1997; Clark et al., 1998; Clark et al., 2000; Condesso de Melo et al., 2001; Corcho Alvarado et al., 2013; Cortecci et al., 2001; Cresswell, Wischusen, et al., 1999; Cronin et al., 2005; Cruz et al., 2005; Cunningham et al., 1998; Currell et al., 2010; Currell et al., 2013; Dafny et al., 2006; Dakin et al., 1983; Darling et al., 1997; Das et al., 1988; Delalande et al., 2008; Dellepere, 1994; Demlie et al., 2007; Dennis et al., 1997; Deng et al., 2009; Derwich et al., 2012; Deshpande et al., 2003; Diamond & Harris, 2000; Diédhiou et al., 2012; Dodo & Zuppi, 1997; Dodo & Zuppi, 1999; Dogramaci et al., 2012; Douglas et al., 2007; Dowgiallo et al., 1990; Dupalová et al., 2012; Dutton, 1995; Eastoe & Rodney, 2014; Eastoe et al., 2014; Edmunds et al., 2002; Edmunds et al., 2003; Edmunds et al., 2006; Edmunds & Wright, 1979; Ellins, 1992; Elliot et al., 1999; Ettayfi et al., 2012; Everdingen et al., 1985; Fadlelmawla et al., 2008; Fang et al., 2015; Farah et al., 2000; Fass et al., 2007; Fernandez‐Chacon et al., 2010; Fernandes & Carreira, 2008; Fontes et al., 1991; Foriz et al., 2005; Fortin et al., 1991; Foto et al., 2012; Fritz et al., 1981; Garfias et al., 2010; Gastmans et al., 2010; Gat & Issar, 1974; Gat & Galai, 1982; Gates, Edmunds, Darling, et al., 2008; van Geldern et al., 2014; Gerber & Howard, 2001; Geyh & Ploethner, 2008; Geyh & Sofner, 1989; Gherardi et al., 2002; Girard et al., 1997; Gonfiantini et al., 1974; Gonfiantini & Simonot, 1987; Goni, 2006; Gomez et al., 2014; Gonzalez Hita et al., 1994; Gouvea da Silva, 1983; Gorgni et al., 1982; Grasby et al., 2010; Grassi & Cortecci, 2005; Greene et al., 2008; Guendouz et al., 2003; Guendouz et al., 2006; Gupta et al., 2005; Han et al., 2011; Haggaz & Kheirallah, 1988; Harrington et al., 2011; Hatipoglu et al., 2009; Heaton et al., 1986; Hedley et al., 2009; He et al., 2012; Heilweil et al., 2009; Helstrup, 2006; Herrera et al., 2006; Hinsby et al., 2001; Horst, 2006; Horst et al., 2007; Horst et al., 2011; Houben et al., 2014; Hoque & Burgess, 2012; Howard & Mullings, 1996; Huang & Pang, 2010; Huff et al., 2012; Hui et al., 2007; Huneau et al., 2011; Hussien, 2010; Iacumin et al., 2009; Ingraham & Matthews, 1988; Iriarte et al., 2006; Iwatsuki et al., 2000; Janik et al., 1991; Janik et al., 1992; Jasechko, 2014; Jasechko, Wassenaar, & Mayer, 2017; Jessen et al., 2008; Jiráková et al., 2009; Jiráková et al., 2010; Jones et al., 2000; Joseph et al., 2011; Jurgens et al., 2008; Kagabu et al., 2011; Kagabu et al., 2013; Kamel et al., 2006; Kamdee et al., 2013; Karro et al., 2004; Kattan, 2001; Kattan, 2006; Keatings et al., 2007; Kebede et al., 2005; Kebede et al., 2007; Kennedy & Genereux, 2007; Khaska et al., 2013; King et al., 2014; Kloppmann et al., 1998; Klump et al., 2008; Koh et al., 2012; Kohfahl et al., 2008; Kulongoski et al., 2004; Kulongoski et al., 2008; Kulongoski et al., 2009; Kortelainen & Karhu, 2004; Külls, 2000; Kumar et al., 2009; Kumar et al., 2011; Kpegli et al., 2015; Kusano et al., 2014; Kreuzer et al., 2009; Lanza, 2009; Lapworth et al., 2012; Larsen et al., 2002; Larsen et al., 2003; Leaney & Allison, 1986; Le Gal La Salle, Fontes, et al., 1995; Le Gal La Salle, Marlin, et al., 1995; Le Gal La Salle et al., 2001; Lehmann et al., 2003; Lemkademe et al., 2011; Leontiadis et al., 1996; Leybourne et al., 2009; J. Li, et al., 2015; Li et al., 2008; Liu et al., 2008; Lorenzen et al., 2012; Lu et al., 2007; Ma & Edmunds, 2006; Ma et al., 2004; Ma et al., 2009; Ma et al., 2010; Ma et al., 2013; Machida et al., 2013; Mack et al., 2014; Madioune et al., 2014; Maduabuchi et al., 2006; Magaritz et al., 1989; Mahlknecht et al., 2006; Maldonado Astudillo et al., 1994; Mandal et al., 2011; Marfia et al., 2004; Margane et al., 2005; Martinelli et al., 2014; Mashiatullah et al., 2000; Matter et al., 2006; Maulé et al., 1994; Mayr et al., 2007; Mažeika et al., 2013; Mazor & Verhagen, 1983; Mazor et al., 1974; Mazor et al., 1995; McKenzie et al., 2001; McKenzie et al., 2010; McMahon et al., 2004; McMahon et al., 2006; Mehta et al., 2000; Mendonca et al., 2005; Mendoza et al., 2006; Michel et al., 2002; Min et al., 2007; Mischke et al., 2010; Mohammadi et al., 2012; Moulla et al., 2012; Möller et al., 2007; Monjerezi et al., 2011; Moore et al., 2006; Moran & Rose, 2003; Morrissey et al., 2010; Mostapa et al., 2011; Moussa et al., 2010; Mukherjee et al., 2007; Mulligan et al., 2011; Murad & Krishnamurthy, 2008; Murad, Garamoon, et al., 2011; Murad, Hussein, et al., 2011; Mutlu et al., 2011; Ndembo et al., 2007; Nieva et al., 1997; Njitchoua & Ngounou Ngatcha, 1997; Njitchoua et al., 1995; Nkotagu, 1996; Noseck et al., 2009; Nurmi et al., 1988; Oberhänsli et al., 2009; Otálvaro et al., 2006; Osborn & McIntosh, 2010; Pang et al., 2013; Panichi et al., 1974; Parizi & Samani, 2014; Pelig‐Ba, 2009; Peng et al., 2012; Phillips et al., 1986; Pilla et al., 2006; Plummer et al., 2004; Plummer et al., 2012; Povinec, Burnett, et al., 2012; Povinec, Zenisova, et al., 2012; Porowski, 2004: Praamsma et al., 2009; Puig et al., 2012; Purdy et al., 1996; Qin et al., 2012; Rachid et al., 2014; Raco et al., 2013; Rahube, 2003; Raidla et al., 2009; Raidla et al., 2012; Rango et al., 2010; Rauert et al., 1993; Reboucas & Santiago, 1989; Reddy et al., 2011; Riddell et al., 2016; Rissmann et al., 2015; Robinson & Gunatilaka, 1991; Rock & Mayer, 2009; Röper et al., 2012; Rosenthal et al., 2007; Sader et al., 2013; Saha et al., 2011; Saka et al., 2013; Salati et al., 1974; van Sambeck et al., 2000; Samborska et al., 2012; Sami, 1992; Sanford & Buapeng, 1996; Santiago et al., 1997; Satrio et al., 2012; Scheiber et al., 2015;Schlegel et al., 2009; Seal & Shanks, 1998; Séguis et al., 2011; Shehata & Al‐Ruwaih, 1999; Shi et al., 2000; Shivanna et al., 2004; Shouakar‐Stash et al., 2007; Siegel, 1991; Sikdar & Sahu, 2009; Silva et al., 1989; Sklash & Mwangi, 1991; Smellie & Wikberg, 1991; Sokolovskii et al., 2012; Solis & Araguas‐Araguas, 1995; Soro & Goula Bi Tie, 1997; de Souza et al., 2015; Squeo et al., 2006; Stadler et al., 2010; Stadler et al., 2012; Stewart, 2012; Stimson et al., 2001; Stoecker et al., 2013; Stotler et al., 2009; Sturchio et al., 1996; Stute & Deák, 1989; Stute & Talma, 1998; Su et al., 2009; Subyani, 2004; Sukhija et al., 2006; Sultan et al., 1997; Sultan et al., 2000; Sultan et al., 2007; Sultan et al., 2008; Sultan, Metwally, et al., 2011; Sultan, Yousef, et al., 2011; Sveinbjornsdottir et al., 1995; Swarzenski et al., 2013; Szocs et al., 2013; Tan et al., 2011; Tantawi et al., 1998; Taupin et al., 2009; Taylor & Evans, 1999; Taylor & Howard, 1996; Taylor, 1994; Taylor, Trompetter, et al., 2001; Tenu et al., 1975; Tenu et al., 1981; Thomas et al., 2003; Tijani et al., 1996; Tosaki, Tase, Kimikazu, et al., 2011; Tosaki, Tase, Kondoh, et al., 2011; Trabelsi et al., 2012; Truesdell et al., 1986; Vaikmäe, Vallner, et al., 2001; Varsányi et al., 1999; Varsányi et al., 2011; Vengosh et al., 2007; Visser et al., 2013; Wallick, 1981; Walraevens, 1990; Wang & Jiao, 2012; Wang et al., 2012; Wang, Hu, et al., 2013; Warrier et al., 2012; Wassenaar et al., 2009; Weyhenmeyer et al., 2000; Weyhenmeyer et al., 2002; Winckel et al., 2002; Wischusen et al., 2004; Wood, 2011; Xie, Wang, Li, et al., 2012; Xie, Wang, Su, et al., 2012; Yangui et al., 2011; Yangui, Abidi, et al., 2012; Yangui, Zouari, et al., 2012; Yechieli et al., 2008; Yin, Hou, Dou, et al., 2011; Yitbarek et al., 2012; Yuan et al., 2011; Zammouri et al., 2007; Zhang et al., 2005; Zhang et al., 2014; Zhu et al., 2007; Zuber et al., 1997; Zuber et al., 2000; Zuber et al., 2004; Zuber, 1983; Дублянский et al., 2012). SMOW = standard mean ocean water.
Groundwater δ¹⁸O measurements made in spring and well waters around the globe. (a) Groundwater isotope measurement locations and δ¹⁸O values. High δ¹⁸O values are common at low latitudes and near coastlines; low δ¹⁸O values are common at high latitudes, high elevations, and continental interiors. Groundwater isotope data are relatively common throughout the contiguous United States, southern Canada, Europe, north and east Africa, north China, Bangladesh, the western islands of the Malay Archipelago, New Zealand, and populated regions of Australia. Groundwater isotope data are relatively sparse across Latin America, southwest Africa, central Asia, eastern Europe, central and southern China, Borneo, New Guinea, and areas of Australia. For example, relatively high‐density and nation‐wide groundwater δ¹⁸O data sets exist for Ireland (Regan et al., 2017), Costa Rica (Sánchez‐Murillo & Birkel, 2016), Uganda (Jasechko, 2014; samples collected with M. GebreEgziabher), Mexico (Wassenaar et al., 2009), India (Bhattacharya et al., 1985), South Africa (West et al., 2014), the United States of America, and Canada (Jasechko, Wassenaar & Mayer, 2017). (b) Groundwater (grey circles) and annual amount‐weighted precipitation (black squares) δ¹⁸O values and their variance with latitude. Precipitation isotope compositions are derived from the International Atomic Energy Agency (www‐naweb.iaea.org/napc/ih/IHS_resources_isohis.html), the United States Network for Isotopes in Precipitation (Welker, 2012) and the Canadian Network for Isotopes in Precipitation (e.g., Birks & Gibson, 2009; Delavau et al., 2011). Precipitation δ¹⁸O values plotted in panel b are ‘amount‐weighted’ over the entire period of record, meaning time‐steps during which more precipitation fell are weighted more than those during which less precipitation fell. Groundwater δ¹⁸O data presented here are derived from the United States' National Water Information System (data downloaded May 2018 from www.waterqualitydata.us) and from data sets compiled from the following n = 435 references (Al Faitouri & Sanford, 2015; Abid et al., 2010; Abid et al., 2011; Abid et al., 2012; Abouelmagd et al., 2014; Abu‐Jaber & Kharabsheh, 2008; Adams et al., 2001; Adiaffi et al., 2009; Adomako et al., 2011; Aeschbach‐Hertig et al., 2002; Aggarwal et al., 2000; Ahmad & Green, 1986; Ahmed et al., 2011; Ako Ako et al., 2012; Al‐Charideh & Abou‐Zakhem, 2010; Al‐Charideh, 2012; Al‐Charideh & Kattan, 2016; Al‐Charideh & Hasan, 2013; Alemayehu et al., 2011; Al‐Katheeri et al., 2009; Allen, 2003; Al‐Mashaikhi et al., 2012; Alpers & Whittemore, 1990; Al‐Ruwaih & Shehata, 2004; Alsaaran, 2005; Alyamani, 2001; Amer et al., 2012; Andre et al., 2005; Andrews et al., 1989; Andrews, Edmunds, et al., 1994; Andrews, Fontes, et al., 1994; Aravena et al., 2003; Arslan et al., 2013; Atkinson et al., 2014; Awad, 2011; Awad et al., 1994; Awad et al., 1997; Awad, 1997; Back et al., 1983; Bahati et al., 2005; Bajjali & Abu‐Jaber, 2001; Bajjali, 2006; Bakari, Aagaard, Vogt, Ruden, Brennwald, et al., 2012; Baker, 2009; Barbecot et al., 2000; Batista, Santiago, Frischkorn, Filho, & Forster, 1998; Bayari et al., 2009; Bennetts et al., 2006; Berg & Pearson, 2012; Beyerle et al., 1998; Beyerle et al., 2003; Bhatia et al., 2011; Bhattacharya et al., 1985; Blomqvist, 1999; Böhlke et al., 1998; Bouchaou et al., 2008; Bouchaou et al., 2009; Bouragba et al., 2011; Boutin, 2009; Bowen et al., 2012; Branchu & Bergonzini, 2004; Bretzler et al., 2011; Brown et al., 2011; Buck et al., 2005; Burg et al., 2013; Bwire Ojiambo et al., 2001; Calmels et al., 2008; Capaccioni et al., 2003; Carneiro et al., 1998; Carreira et al., 2011; Carreira, Marques & Nunes, 2014; Carrillo‐Rivera et al., 1992; Cartwright et al., 2012; Cartwight & Morgenstern, 2012; Cartwright & Weaver, 2005; Castany et al., 1974; Celle‐Jeanton et al., 2009; Cheikh et al., 2012; Chen et al., 2003; Chen et al., 2005; Chen et al., 2011; Chen et al., 2012; Chen et al., 2014; Cheung & Mayer, 2009; Choi et al., 2005; Ciezkowski et al., 1992; Cidu & Bahaj, 2000; Clark et al., 1987; Clark et al., 1997; Clark et al., 1998; Clark et al., 2000; Condesso de Melo et al., 2001; Corcho Alvarado et al., 2013; Cortecci et al., 2001; Cresswell, Wischusen, et al., 1999; Cronin et al., 2005; Cruz et al., 2005; Cunningham et al., 1998; Currell et al., 2010; Currell et al., 2013; Dafny et al., 2006; Dakin et al., 1983; Darling et al., 1997; Das et al., 1988; Delalande et al., 2008; Dellepere, 1994; Demlie et al., 2007; Dennis et al., 1997; Deng et al., 2009; Derwich et al., 2012; Deshpande et al., 2003; Diamond & Harris, 2000; Diédhiou et al., 2012; Dodo & Zuppi, 1997; Dodo & Zuppi, 1999; Dogramaci et al., 2012; Douglas et al., 2007; Dowgiallo et al., 1990; Dupalová et al., 2012; Dutton, 1995; Eastoe & Rodney, 2014; Eastoe et al., 2014; Edmunds et al., 2002; Edmunds et al., 2003; Edmunds et al., 2006; Edmunds & Wright, 1979; Ellins, 1992; Elliot et al., 1999; Ettayfi et al., 2012; Everdingen et al., 1985; Fadlelmawla et al., 2008; Fang et al., 2015; Farah et al., 2000; Fass et al., 2007; Fernandez‐Chacon et al., 2010; Fernandes & Carreira, 2008; Fontes et al., 1991; Foriz et al., 2005; Fortin et al., 1991; Foto et al., 2012; Fritz et al., 1981; Garfias et al., 2010; Gastmans et al., 2010; Gat & Issar, 1974; Gat & Galai, 1982; Gates, Edmunds, Darling, et al., 2008; van Geldern et al., 2014; Gerber & Howard, 2001; Geyh & Ploethner, 2008; Geyh & Sofner, 1989; Gherardi et al., 2002; Girard et al., 1997; Gonfiantini et al., 1974; Gonfiantini & Simonot, 1987; Goni, 2006; Gomez et al., 2014; Gonzalez Hita et al., 1994; Gouvea da Silva, 1983; Gorgni et al., 1982; Grasby et al., 2010; Grassi & Cortecci, 2005; Greene et al., 2008; Guendouz et al., 2003; Guendouz et al., 2006; Gupta et al., 2005; Han et al., 2011; Haggaz & Kheirallah, 1988; Harrington et al., 2011; Hatipoglu et al., 2009; Heaton et al., 1986; Hedley et al., 2009; He et al., 2012; Heilweil et al., 2009; Helstrup, 2006; Herrera et al., 2006; Hinsby et al., 2001; Horst, 2006; Horst et al., 2007; Horst et al., 2011; Houben et al., 2014; Hoque & Burgess, 2012; Howard & Mullings, 1996; Huang & Pang, 2010; Huff et al., 2012; Hui et al., 2007; Huneau et al., 2011; Hussien, 2010; Iacumin et al., 2009; Ingraham & Matthews, 1988; Iriarte et al., 2006; Iwatsuki et al., 2000; Janik et al., 1991; Janik et al., 1992; Jasechko, 2014; Jasechko, Wassenaar, & Mayer, 2017; Jessen et al., 2008; Jiráková et al., 2009; Jiráková et al., 2010; Jones et al., 2000; Joseph et al., 2011; Jurgens et al., 2008; Kagabu et al., 2011; Kagabu et al., 2013; Kamel et al., 2006; Kamdee et al., 2013; Karro et al., 2004; Kattan, 2001; Kattan, 2006; Keatings et al., 2007; Kebede et al., 2005; Kebede et al., 2007; Kennedy & Genereux, 2007; Khaska et al., 2013; King et al., 2014; Kloppmann et al., 1998; Klump et al., 2008; Koh et al., 2012; Kohfahl et al., 2008; Kulongoski et al., 2004; Kulongoski et al., 2008; Kulongoski et al., 2009; Kortelainen & Karhu, 2004; Külls, 2000; Kumar et al., 2009; Kumar et al., 2011; Kpegli et al., 2015; Kusano et al., 2014; Kreuzer et al., 2009; Lanza, 2009; Lapworth et al., 2012; Larsen et al., 2002; Larsen et al., 2003; Leaney & Allison, 1986; Le Gal La Salle, Fontes, et al., 1995; Le Gal La Salle, Marlin, et al., 1995; Le Gal La Salle et al., 2001; Lehmann et al., 2003; Lemkademe et al., 2011; Leontiadis et al., 1996; Leybourne et al., 2009; J. Li, et al., 2015; Li et al., 2008; Liu et al., 2008; Lorenzen et al., 2012; Lu et al., 2007; Ma & Edmunds, 2006; Ma et al., 2004; Ma et al., 2009; Ma et al., 2010; Ma et al., 2013; Machida et al., 2013; Mack et al., 2014; Madioune et al., 2014; Maduabuchi et al., 2006; Magaritz et al., 1989; Mahlknecht et al., 2006; Maldonado Astudillo et al., 1994; Mandal et al., 2011; Marfia et al., 2004; Margane et al., 2005; Martinelli et al., 2014; Mashiatullah et al., 2000; Matter et al., 2006; Maulé et al., 1994; Mayr et al., 2007; Mažeika et al., 2013; Mazor & Verhagen, 1983; Mazor et al., 1974; Mazor et al., 1995; McKenzie et al., 2001; McKenzie et al., 2010; McMahon et al., 2004; McMahon et al., 2006; Mehta et al., 2000; Mendonca et al., 2005; Mendoza et al., 2006; Michel et al., 2002; Min et al., 2007; Mischke et al., 2010; Mohammadi et al., 2012; Moulla et al., 2012; Möller et al., 2007; Monjerezi et al., 2011; Moore et al., 2006; Moran & Rose, 2003; Morrissey et al., 2010; Mostapa et al., 2011; Moussa et al., 2010; Mukherjee et al., 2007; Mulligan et al., 2011; Murad & Krishnamurthy, 2008; Murad, Garamoon, et al., 2011; Murad, Hussein, et al., 2011; Mutlu et al., 2011; Ndembo et al., 2007; Nieva et al., 1997; Njitchoua & Ngounou Ngatcha, 1997; Njitchoua et al., 1995; Nkotagu, 1996; Noseck et al., 2009; Nurmi et al., 1988; Oberhänsli et al., 2009; Otálvaro et al., 2006; Osborn & McIntosh, 2010; Pang et al., 2013; Panichi et al., 1974; Parizi & Samani, 2014; Pelig‐Ba, 2009; Peng et al., 2012; Phillips et al., 1986; Pilla et al., 2006; Plummer et al., 2004; Plummer et al., 2012; Povinec, Burnett, et al., 2012; Povinec, Zenisova, et al., 2012; Porowski, 2004: Praamsma et al., 2009; Puig et al., 2012; Purdy et al., 1996; Qin et al., 2012; Rachid et al., 2014; Raco et al., 2013; Rahube, 2003; Raidla et al., 2009; Raidla et al., 2012; Rango et al., 2010; Rauert et al., 1993; Reboucas & Santiago, 1989; Reddy et al., 2011; Riddell et al., 2016; Rissmann et al., 2015; Robinson & Gunatilaka, 1991; Rock & Mayer, 2009; Röper et al., 2012; Rosenthal et al., 2007; Sader et al., 2013; Saha et al., 2011; Saka et al., 2013; Salati et al., 1974; van Sambeck et al., 2000; Samborska et al., 2012; Sami, 1992; Sanford & Buapeng, 1996; Santiago et al., 1997; Satrio et al., 2012; Scheiber et al., 2015;Schlegel et al., 2009; Seal & Shanks, 1998; Séguis et al., 2011; Shehata & Al‐Ruwaih, 1999; Shi et al., 2000; Shivanna et al., 2004; Shouakar‐Stash et al., 2007; Siegel, 1991; Sikdar & Sahu, 2009; Silva et al., 1989; Sklash & Mwangi, 1991; Smellie & Wikberg, 1991; Sokolovskii et al., 2012; Solis & Araguas‐Araguas, 1995; Soro & Goula Bi Tie, 1997; de Souza et al., 2015; Squeo et al., 2006; Stadler et al., 2010; Stadler et al., 2012; Stewart, 2012; Stimson et al., 2001; Stoecker et al., 2013; Stotler et al., 2009; Sturchio et al., 1996; Stute & Deák, 1989; Stute & Talma, 1998; Su et al., 2009; Subyani, 2004; Sukhija et al., 2006; Sultan et al., 1997; Sultan et al., 2000; Sultan et al., 2007; Sultan et al., 2008; Sultan, Metwally, et al., 2011; Sultan, Yousef, et al., 2011; Sveinbjornsdottir et al., 1995; Swarzenski et al., 2013; Szocs et al., 2013; Tan et al., 2011; Tantawi et al., 1998; Taupin et al., 2009; Taylor & Evans, 1999; Taylor & Howard, 1996; Taylor, 1994; Taylor, Trompetter, et al., 2001; Tenu et al., 1975; Tenu et al., 1981; Thomas et al., 2003; Tijani et al., 1996; Tosaki, Tase, Kimikazu, et al., 2011; Tosaki, Tase, Kondoh, et al., 2011; Trabelsi et al., 2012; Truesdell et al., 1986; Vaikmäe, Vallner, et al., 2001; Varsányi et al., 1999; Varsányi et al., 2011; Vengosh et al., 2007; Visser et al., 2013; Wallick, 1981; Walraevens, 1990; Wang & Jiao, 2012; Wang et al., 2012; Wang, Hu, et al., 2013; Warrier et al., 2012; Wassenaar et al., 2009; Weyhenmeyer et al., 2000; Weyhenmeyer et al., 2002; Winckel et al., 2002; Wischusen et al., 2004; Wood, 2011; Xie, Wang, Li, et al., 2012; Xie, Wang, Su, et al., 2012; Yangui et al., 2011; Yangui, Abidi, et al., 2012; Yangui, Zouari, et al., 2012; Yechieli et al., 2008; Yin, Hou, Dou, et al., 2011; Yitbarek et al., 2012; Yuan et al., 2011; Zammouri et al., 2007; Zhang et al., 2005; Zhang et al., 2014; Zhu et al., 2007; Zuber et al., 1997; Zuber et al., 2000; Zuber et al., 2004; Zuber, 1983; Дублянский et al., 2012). SMOW = standard mean ocean water.
… 
Global precipitation and groundwater isotope compositions. Panel (a) presents global precipitation δ¹⁸O and δ²H data (n = 68,382 samples). Panel (b) is a schematic of some of the processes that may alter stable O and H isotopic compositions of groundwaters. High‐temperature water‐rock interactions may increase δ¹⁸O values more so than δ²H values—yielding low deuterium excess values (Giggenbach, 1992). Low temperature water‐rock interactions may decrease δ¹⁸O values—in some cases leading to high deuterium excess values (examples limited mostly to deep crystalline basement brines; Kloppmann et al., 2002). Methanogensis may increase δ²H values with minimal impact on δ¹⁸O values—leading to high deuterium excess values. Partial evaporation may increase both δ²H and δ¹⁸O values along δ²H/δ¹⁸O slopes of ~3 to ~6—leading to low deuterium excess values. δ²H/δ¹⁸O slopes tend to be lower under low‐humidity conditions and where evaporation takes place from soils (e.g., δ²H/δ¹⁸O slopes of ~2 to ~5); δ²H/δ¹⁸O evaporation slopes tend to be higher for open water evaporation under humid condi‐tions (e.g., δ²H/δ¹⁸O slopes of ~5 to ~8). The great majority (90%) of compiled groundwater isotope compositions have deuterium excess values of between 0‰ and 20‰. A global regression of precipitation isotope compositions is labeled “meteoric waters” and follows δ²H = 8 × δ¹⁸O + 10 (the global meteoric water line; Craig, 1961). Deuterium excess (d) is calculated, following d = δ²H − 8 × δ¹⁸O (Dansgaard, 1964). Panel (b) is based partly on schematic presented by Horita (2005). Last, panel (c) presents compiled groundwater isotope compositions (n = 44,948 samples). A linear regression describing groundwater δ²H variations with groundwater δ¹⁸O is similar for the linear regression describing precipitation δ²H and δ¹⁸O values (from panel a). SMOW = standard mean ocean water.
Global precipitation and groundwater isotope compositions. Panel (a) presents global precipitation δ¹⁸O and δ²H data (n = 68,382 samples). Panel (b) is a schematic of some of the processes that may alter stable O and H isotopic compositions of groundwaters. High‐temperature water‐rock interactions may increase δ¹⁸O values more so than δ²H values—yielding low deuterium excess values (Giggenbach, 1992). Low temperature water‐rock interactions may decrease δ¹⁸O values—in some cases leading to high deuterium excess values (examples limited mostly to deep crystalline basement brines; Kloppmann et al., 2002). Methanogensis may increase δ²H values with minimal impact on δ¹⁸O values—leading to high deuterium excess values. Partial evaporation may increase both δ²H and δ¹⁸O values along δ²H/δ¹⁸O slopes of ~3 to ~6—leading to low deuterium excess values. δ²H/δ¹⁸O slopes tend to be lower under low‐humidity conditions and where evaporation takes place from soils (e.g., δ²H/δ¹⁸O slopes of ~2 to ~5); δ²H/δ¹⁸O evaporation slopes tend to be higher for open water evaporation under humid condi‐tions (e.g., δ²H/δ¹⁸O slopes of ~5 to ~8). The great majority (90%) of compiled groundwater isotope compositions have deuterium excess values of between 0‰ and 20‰. A global regression of precipitation isotope compositions is labeled “meteoric waters” and follows δ²H = 8 × δ¹⁸O + 10 (the global meteoric water line; Craig, 1961). Deuterium excess (d) is calculated, following d = δ²H − 8 × δ¹⁸O (Dansgaard, 1964). Panel (b) is based partly on schematic presented by Horita (2005). Last, panel (c) presents compiled groundwater isotope compositions (n = 44,948 samples). A linear regression describing groundwater δ²H variations with groundwater δ¹⁸O is similar for the linear regression describing precipitation δ²H and δ¹⁸O values (from panel a). SMOW = standard mean ocean water.
… 
Some scenarios that may lead to the condition: groundwater δ¹⁸O > amount‐weighted annual precipitation δ¹⁸O. These include (a) high‐temperature alteration of the parent groundwater δ¹⁸O values (Giggenbach, 1992; Giggenbach & Soto, 1992); (b) higher summer recharge/precipitation ratios than winter recharge/precipitation ratios; (c) partial evaporation of meteoric water prior to, or during, infiltration (e.g., Cartwright et al., 2004; Huang & Pang, 2010; Njitchoua & Ngounou Ngatcha, 1997; Salem & El‐Sayed, 2015); (d) replenishment of coastal or (sub)tropical aquifers during older, different climate conditions than present (e.g., Clark et al., 1997; Plummer, 1993; Stute & Talma, 1998); and/or (e) transport of meteoric water over long distances before it recharges the aquifer either naturally (e.g., losing reach of a river; Darling et al., 1987; Baskaran et al., 2009) or through diversion to meet human water demands (e.g., Criss & Davisson, 1996; Plummer et al., 2000).
Some scenarios that may lead to the condition: groundwater δ¹⁸O > amount‐weighted annual precipitation δ¹⁸O. These include (a) high‐temperature alteration of the parent groundwater δ¹⁸O values (Giggenbach, 1992; Giggenbach & Soto, 1992); (b) higher summer recharge/precipitation ratios than winter recharge/precipitation ratios; (c) partial evaporation of meteoric water prior to, or during, infiltration (e.g., Cartwright et al., 2004; Huang & Pang, 2010; Njitchoua & Ngounou Ngatcha, 1997; Salem & El‐Sayed, 2015); (d) replenishment of coastal or (sub)tropical aquifers during older, different climate conditions than present (e.g., Clark et al., 1997; Plummer, 1993; Stute & Talma, 1998); and/or (e) transport of meteoric water over long distances before it recharges the aquifer either naturally (e.g., losing reach of a river; Darling et al., 1987; Baskaran et al., 2009) or through diversion to meet human water demands (e.g., Criss & Davisson, 1996; Plummer et al., 2000).
… 
Some scenarios that may lead to the condition: groundwater δ¹⁸O < amount‐weighted annual precipitation δ¹⁸O. These include (a) groundwater aquifers replenished in part by precipitation that fell at higher elevations than the land surface at the location that the sample was collected (e.g., Gonfiantini et al., 1976; Payne & Yurtsever, 1974); (b) recharge of surface waters diverted for agricultural, domestic or industrial uses (e.g., Williams & Rodoni, 1997); (c) disproportionate recharge from intensive rainfall, in places where precipitation rates and δ¹⁸O values correlate inversely (e.g., Geirnaert et al., 1984; Vogel & Van Urk, 1975); (d) higher recharge/precipitation ratios for cold‐season precipitation relative to warm‐season precipitation (e.g., Brinkmann et al., 1963; Simpson et al., 1970); (e) retention of groundwater derived from precipitation during the late‐Pleistocene, when global atmospheric temperatures were as much as ~4°C cooler‐than present (e.g., Gonfiantini et al., 1974; Phillips et al., 1986; Vogel & Ehhalt, 1963); and (f) transport of waters from a place where precipitation δ¹⁸O values are relatively low to another place where precipitation δ¹⁸O values are relatively high before the water recharges (e.g., Liu & Yamanaka, 2012). These processes are not mutually exclusive; more than one may affect groundwater isotope compositions (e.g., Liu & Yamanaka, 2012). Decoupling these various processes can be challenging and requires consideration of local hydroclimate and hydrogeologic conditions (read, e.g., Uliana et al., 2007).
+27
Some scenarios that may lead to the condition: groundwater δ¹⁸O < amount‐weighted annual precipitation δ¹⁸O. These include (a) groundwater aquifers replenished in part by precipitation that fell at higher elevations than the land surface at the location that the sample was collected (e.g., Gonfiantini et al., 1976; Payne & Yurtsever, 1974); (b) recharge of surface waters diverted for agricultural, domestic or industrial uses (e.g., Williams & Rodoni, 1997); (c) disproportionate recharge from intensive rainfall, in places where precipitation rates and δ¹⁸O values correlate inversely (e.g., Geirnaert et al., 1984; Vogel & Van Urk, 1975); (d) higher recharge/precipitation ratios for cold‐season precipitation relative to warm‐season precipitation (e.g., Brinkmann et al., 1963; Simpson et al., 1970); (e) retention of groundwater derived from precipitation during the late‐Pleistocene, when global atmospheric temperatures were as much as ~4°C cooler‐than present (e.g., Gonfiantini et al., 1974; Phillips et al., 1986; Vogel & Ehhalt, 1963); and (f) transport of waters from a place where precipitation δ¹⁸O values are relatively low to another place where precipitation δ¹⁸O values are relatively high before the water recharges (e.g., Liu & Yamanaka, 2012). These processes are not mutually exclusive; more than one may affect groundwater isotope compositions (e.g., Liu & Yamanaka, 2012). Decoupling these various processes can be challenging and requires consideration of local hydroclimate and hydrogeologic conditions (read, e.g., Uliana et al., 2007).
… 
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Global Isotope Hydrogeology―Review
Scott Jasechko
1
1
Bren School of Environmental Science and Management, University of California, Santa Barbara, CA, USA
Abstract Groundwater
18
O/
16
O,
2
H/
1
H,
13
C/
12
C,
3
H, and
14
C data can help quantify molecular
movements and chemical reactions governing groundwater recharge, quality, storage, flow, and
discharge. Here, commonly applied approaches to isotopic data analysis are reviewed, involving
groundwater recharge seasonality, recharge elevations, groundwater ages, paleoclimate conditions, and
groundwater discharge. Reviewed works confirm and quantify long held tenets: (i) that recharge derives
disproportionately from wet season and winter precipitation; (ii) that modern groundwaters comprise little
global groundwater; (iii) that “fossil”(>12,000‐year‐old) groundwaters dominate global aquifer storage; (iv)
that fossil groundwaters capture late‐Pleistocene climate conditions; (v) that surface‐borne contaminants
are more common in younger groundwaters; and (vi) that groundwater discharges generate substantial
streamflow. Groundwater isotope data are disproportionately common to midlatitudes and sedimentary
basins equipped for irrigated agriculture, but less plentiful across high latitudes, hyperarid deserts, and
equatorial rainforests. Some of these underexplored aquifer systems may be suitable targets for future
field testing.
Plain Language Summary Water from the underground—groundwater—is the primary water
supply to billions of humans. Understanding how groundwater originates and where it flows is important
so that groundwater can be protected from pollution and overuse. One of the ways that scientists learn
about groundwater is by measuring the abundances of heavier and lighter forms of elements in the
groundwater. These isotopes help scientists map where groundwater comes from, measure how long it
spends under the ground, and realize how important it is for generating river flows. This manuscript reviews
the ways that measuring isotopes have helped scientists understand water resources and suggests ways that
isotopes can contribute to understanding global groundwater resources even better.
Table of Contents
1. Isotope hydrogeology ......................................................................................................................................... 6
1.1 Review motivation, objectives and structure ...........................................................................................6
1.2 Brief overview of groundwater O, H and dissolved inorganic C isotope systematics..................... 12
1.3 Stable oxygen and hydrogen isotope systematics................................................................................. 15
1.4 Radioactive hydrogen isotope systematics ............................................................................................ 26
1.5 Stable dissolved inorganic carbon isotope systematics ........................................................................ 32
1.6 Radioactive dissolved inorganic carbon isotope systematics .............................................................. 35
2. Recharge sources and elevations.................................................................................................................... 38
2.1 Background and importance ................................................................................................................... 38
2.2 Approach.................................................................................................................................................... 41
2.3 Applications ............................................................................................................................................... 46
2.4 Limitations ................................................................................................................................................. 53
2.5 Opportunities............................................................................................................................................. 57
3. Seasonal biases in groundwater recharge ..................................................................................................... 59
3.1 Background and importance ................................................................................................................... 59
3.2 Approach.................................................................................................................................................... 61
3.3 Applications ............................................................................................................................................... 62
3.4 Limitations ................................................................................................................................................. 70
3.5 Opportunities............................................................................................................................................. 74
©2019. American Geophysical Union.
All Rights Reserved.
REVIEW ARTICLE
10.1029/2018RG000627
Key Points:
•Global isotopic data quantify
molecular movements and chemical
reactions governing groundwater
recharge, storage, and discharge
•Isotope measurements have been
made in >100,000 well water and
spring samples from >1,000 globally
distributed aquifer systems
•This review presents global analyses
of recharge seasonality, recharge
elevations, groundwater age,
groundwater discharges to rivers,
and young versus old streamflow
Correspondence to:
S. Jasechko,
jasechko@ucsb.edu
Citation:
Jasechko, S. (2019). Global isotope
hydrogeology―review. Reviews of
Geophysics,57 https://doi.org/
10.1029/2018RG000627
Received 18 OCT 2018
Accepted 17 APR 2019
Accepted article online 29 APR 2019
This article was corrected on 02 SEP
2019. See the end of the full text for
details.
JASECHKO
Published online 12 AUG 2019
, 835–965.
835
4. Threshold rainfall intensities for recharge ................................................................................................... 76
4.1 Background and importance ................................................................................................................... 76
4.2 Approach.................................................................................................................................................... 77
4.3 Applications ............................................................................................................................................... 79
4.4 Limitations ................................................................................................................................................. 84
4.5 Opportunities............................................................................................................................................. 88
5. ‘Modern’groundwater ..................................................................................................................................... 88
5.1 Background and importance ................................................................................................................... 88
5.2 Approach.................................................................................................................................................... 90
5.3 Applications ............................................................................................................................................... 92
5.4 Limitations ................................................................................................................................................. 97
5.5 Opportunities............................................................................................................................................. 98
6. ‘Fossil’groundwater....................................................................................................................................... 100
6.1 Background and importance ................................................................................................................. 100
6.2 Approach.................................................................................................................................................. 101
6.3 Applications ............................................................................................................................................. 104
6.4 Limitations ............................................................................................................................................... 107
6.5 Opportunities........................................................................................................................................... 108
7. Paleoclimate conditions ................................................................................................................................. 109
7.1 Background and importance ................................................................................................................. 109
7.2 Approach.................................................................................................................................................. 110
7.3 Applications ............................................................................................................................................. 117
7.4 Limitations ............................................................................................................................................... 123
7.5 Opportunities........................................................................................................................................... 133
8. Groundwater discharges to rivers ................................................................................................................ 135
8.1 Background and importance ................................................................................................................. 135
8.2 Approach.................................................................................................................................................. 133
8.3 Applications ............................................................................................................................................. 139
8.4 Limitations ............................................................................................................................................... 146
8.5 Opportunities........................................................................................................................................... 147
9. River water ages.............................................................................................................................................. 151
9.1 Background and importance ................................................................................................................. 151
9.2 Approach.................................................................................................................................................. 152
9.3 Applications ............................................................................................................................................. 154
9.4 Limitations ............................................................................................................................................... 157
9.5 Opportunities........................................................................................................................................... 159
10. Summary and Outlook ................................................................................................................................... 161
1. Isotope hydrogeology
1.1. Review Motivation, Objectives, and Structure
Isotope hydrogeology studies processes and reactions during the recharge, storage, and discharge of ground-
water. Understanding recharge, storage, and discharge is important because groundwater is a strategic fresh
water resource that supplies ~40% of global irrigation and, in places, is the only perennial drinking water
source (Aeschbach‐Hertig & Gleeson, 2012; Alley & Alley, 2017; Famiglietti, 2014; Foster et al., 2000;
Foster & Chilton, 2003; Gorelick & Zheng, 2015; Kundzewicz & Döll, 2009; Shiklomanov, 2000; Taylor,
Scanlon, et al., 2013; Villholth, 2006). Despite its importance, groundwater remains poorly understood.
This is especially true at expansive “regional,”“continental,”or “global”scales spanning hundreds to thou-
sands of kilometers. Yet recent research advances in remote sensing (Chen et al., 2016; Famiglietti & Rodell,
2013; Jung et al., 2010; McColl et al., 2017; Miralles et al., 2011; Richey et al., 2015; Rodell et al., 2004, 2009,
2018; Zhang et al., 2010, 2015), hydrologic modeling (Befus et al., 2017; Clark et al., 2015; Fan et al., 2013;
10.1029/2018RG000627
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JASECHKO 836
Gleeson et al., 2012, 2016; Müller Schmied et al., 2014; Pokhrel et al., 2015; Sawyer et al., 2016; Wada et al.,
2010; Wada, van Beek, & Bierkens, 2012; Wada, van Beek, Weiland, et al., 2012; Wada et al., 2013, 2014;
Wood et al., 2011), food‐energy‐water linkages and “virtual water”(Dalin, Konar, et al., 2012; Dalin,
Suweis, et al., 2012; Dalin et al., 2017; D'Odorico et al., 2014, 2018; Konar et al., 2011; Oki et al., 2017;
Perrone et al., 2011; Perrone & Hornberger, 2014; Rulli et al., 2013; Sivapalan et al., 2014), and water man-
agement (e.g., Altchenko & Villholth, 2013; Nelson, 2018; Nelson & Perrone, 2016; Nijsten et al., 2018;
Rohde et al., 2017; Villholth, 2013a, 2013b) continue to pull hydrology toward global scales (Eagleson,
1986; Famiglietti et al., 2015; Fan, 2015; Vörösmarty et al., 2015).
This manuscript—focused to the field of isotope hydrogeology—reviews available data, methodological
advances and their limitations, lessons drawn from decades of research, and existing knowledge gaps.
This review is motivated by (i) the importance of understanding groundwater renewal, quality, and transport
by way of numerous approaches, of which isotope hydrogeology is one; (ii) the absence of a global‐scale
assessment of the locations where isotope hydrogeology research has, and has not been, completed; and
(iii) the lack of a global‐in‐scale evaluation of regional differences in hydrologic processes elucidated by
isotopic research.
Isotope hydrogeology entails measuring stable or radioactive isotope compositions of river, spring, and well
water samples, then interpreting isotopic measurements to quantify or conceptualize groundwater flow
paths, velocities, and biogeochemical reactions. Groundwater isotope compositions trace movements of
molecules, in cases providing information beyond what can be inferred from piezometric, geophysical, or
solute concentration data alone. Isotope hydrogeology is a subfield of water resources research. It focuses
on the fluxes and chemical reactions governing terrestrial water transport and solute concentrations.
Isotopic techniques can help water scientists identify processes relevant to groundwater quality and sustain-
ability research, and are best applied in conjunction with more conventional hydrogeological data including
piezometric, lithologic, meteorologic, and solute concentration measurements.
The review begins by briefly introducing of oxygen, hydrogen, and carbon isotope systematics (subsections
1.3–1.6). Readers already familiar with isotope systematics can consider skipping to section 2. Following
these introductory subsections, this manuscript reviews commonly applied isotopic techniques that can,
in cases, develop more sophisticated and quantitative conceptual models of groundwater recharge (sections
2–4), storage (sections 5–6), and discharge (sections 7 and 8; Figure 1).
Groundwater recharge (sections 2–4) occurs as water percolates through overlying unsaturated zones to
become stored in an aquifer system. Groundwater recharge is defined by “the downward flow of water
reaching the groundwater table, adding to groundwater storage”(quoting Healy, 2010), or as “water that
moves from the unsaturated zone into the saturated zone”(quoting Nimmo et al., 2005). The term
“recharge”is subdivided into “diffuse”—recharge distributed across expansive areas that occurs as precipi-
tation infiltrates then traverses the unsaturated zone to reach the water table—and “focused”—recharge
derived from the translocation of surface waters such as lakes, rivers, wetlands, and canals into aquifer sto-
rage (e.g., Healy, 2010). Identifying recharge sources and mechanisms is important in order to protect
groundwater supplies from pollution and to understand the ways that groundwater pumping impacts
groundwater storage and discharge. Groundwater isotope compositions can identify recharge areas and
quantify recharge rates and as such can be used as an input to water budget analyses (e.g., Cartwright
et al., 2017; Petersen et al., 2018). Sections 2 through 4 review common isotope‐based techniques applied
to assess groundwater recharge. Specifically, these include testing for focused recharge from rivers, lakes,
and irrigation waters and identifying recharge areas and elevations (section 2), quantifying relative contribu-
tions of winter versus summer precipitation to recharge (section 3), and evaluating the relative importance
of intensive versus less‐intensive rainfall for recharge (section 4).
Groundwater storage and transport in aquifers (sections 5–6) impact the quality and availability of ground-
water resources. Isotopic compositions of stored groundwaters can distinguish flow networks through het-
erogeneous aquifers and, in cases, provide information about paleoclimate conditions (section 6). This
manuscript devotes three sections to techniques used to understand groundwater storage: the abundance
of “modern”groundwater comprised of precipitation that fell within the past ~50 years (section 5); volumes
and vulnerabilities of fossil groundwater replenished before the current “Holocene”epoch began ~12,000
years ago (section 6); and past climate conditions captured by fossil groundwater chemistry (section 7).
10.1029/2018RG000627
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JASECHKO 837
Groundwater discharges (sections 8 and 9) generate streamflow, providing perennial aquatic habitat and
reliable surface water flows for humanity. These final two sections review approaches designed to detect
groundwater discharges into rivers (“hydrograph separations”; section 8) and to quantify streamflow
generated by water stored in the watershed for at least a few months, some of which may be groundwater
(section 9).
By sequentially discussing recharge (sections 2–4), storage (sections 5–7), and then discharge (sections 8
and 9), this review mimics the hydrogeological cycle—where water enters, traverses, and then exits aquifers.
Review objectives include (i) discussing the relevance of isotope‐based approaches to water management
and hydrological sciences (subsections entitled “Background and importance”; e.g., section 2.1); (ii) synthe-
sizing methodologies applied to interpret groundwater carbon (
12
C,
13
C, and
14
C), hydrogen (
1
H,
2
H, and
3
H), and oxygen (
16
O,
17
O, and
18
O) isotopic data (subsections entitled “Approach”; e.g., section 2.2); (iii)
analyzing what has been learned about global water resources since the onset of groundwater isotope
hydrology in the 1950s (subsections entitled “Applications”; e.g., section 2.3); (iv) critiquing current
Figure 1. Common hydrogeological interpretations based on groundwater isotope compositions. Each of the circles is reviewed in the forthcoming subsections
(see section numbers aside each circle). Circles along the top portion of the figure relate to groundwater recharge (sections 2–4); circles along the left side
of the figure relate to the isotope composition of groundwater stored in aquifers and pumped from wells (sections 5–6); and circles on the lower‐right side of the
figure depict groundwater discharges (sections 7 and 8).
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approaches and highlighting limits to their use (subsections entitled “Limitations”; e.g., section 2.4); and (v)
highlighting opportunities to apply isotopic techniques to address broader knowledge gaps in the hydrologi-
cal sciences (subsections entitled “Opportunities”; e.g., section 2.5).
The review is constrained in a number of ways. The techniques described here are not—nor are they
intended to represent—a comprehensive catalog of all isotope‐based approaches in hydrogeology; isotope
hydrogeology is too extensive a subfield. Constraints include (i) concentration solely upon the most com-
monly measured isotopic systems in hydrogeology (i.e., carbon, hydrogen, and oxygen isotope contents),
(ii) discussion only of oxygen and hydrogen isotope measurements of the water molecule itself (i.e., exclud-
ing, for example, oxygen isotope compositions of sulfate or nitrate) and carbon isotope measurements for the
dissolved inorganic phase alone (excluding, for example, groundwater methane carbon isotope systematics),
and (iii) coverage of techniques relating most closely to the interpretation of groundwater isotope composi-
tions, while holding back from a review of techniques relating more closely to other water stores (e.g., soil
and plant xylem waters; e.g., Allison & Hughes, 1974; Dawson, 1993). Information about some of these other
isotope‐based techniques can be found in texts by Clark and Fritz (1997), Kendall and McDonnell (1998), or
Cook and Herczeg (2000).
The work differs from existing reviews by combining a continental‐scale scope, presentation of compiled glo-
bal groundwater isotope data, discussion of commonly applied isotopic approaches, and synthesis of hun-
dreds of published interpretations of groundwater isotopic data in an effort to compare findings from
differing study sites (e.g., Tables 4, 5, 7, 9, and 10). By mapping study sites around the globe, this review also
demonstrates regional sampling biases that may be considered when selecting study sites, should diversify-
ing field areas be a priority.
1.2. Brief Overview of Groundwater O, H, and Dissolved Inorganic C Isotope Systematics
Isotopic measurements from tens of thousands of groundwater samples pumped from hundreds of globally
distributed aquifer systems have helped hydrologists test and solidify numerous tenets (e.g., Payne &
Yurtsever, 1974; Salati et al., 1979; Simpson et al., 1970; Sklash & Farvolden, 1979; Vogel & Ehhalt, 1963).
Isotope compositions of carbon (
12
C,
13
C, and
14
C), hydrogen (
1
H,
2
H, and
3
H), and oxygen (
16
O,
17
O, and
18
O) have been the most widely measured and are the only isotopic systems discussed herein. These initial
subsections (1.2–1.6) briefly review processes influencing groundwater carbon, hydrogen, and oxygen iso-
tope compositions; these sections present primary compiled data, in an effort to make statements more data
driven (Table 1).
The following discussion of stable carbon, oxygen, and hydrogen isotope composition discusses two types
of “isotope effects”(i.e., isotope chemistry; Bigeleisen, 1965) that lead to “isotopic fractionation”—defined
as the partitioning of heavy versus light isotopes in exchange reactions. Two types of isotopic fractiona-
tion are (i) equilibrium isotopic fractionation—generally associated with reversible reactions (e.g., liquid‐
vapor molecular exchanges where the air overlying the water is saturated)—and (ii) kinetic isotopic
fractionation—generally associated with irreversible reactions (e.g., the evaporation of free water into
subsaturated air).
i Equilibrium fractionation, as its title implies, describes chemical exchange for two coexisting phases
under thermodynamic equilibrium. In brief, because molecular vibrational frequencies are correlated
inversely with molecular mass, “isotopologues”(i.e., chemical species having one or more atoms with
a different number of neutrons) of differing molecular mass also have different vibrational frequencies
(Bigeleisen & Mayer, 1947; Chacko et al., 2001). For example, all else being equal, “heavier”water iso-
topologues (e.g.,
1
H
2
H
16
O) will have lower vibrational frequencies than lighter water isotopologues
(e.g.,
1
H
1
H
16
O). Further, these heavier isotopologues with lower vibrational frequencies will be more
energetically stable than their lighter counterparts (because of differences in zero‐point energies;
Bigeleisen, 1965). It follows that any substance (e.g., ice, water, and vapor) is energetically stabilized
by heavy isotope substitution; equilibrium fractionation arises due to the differing preferences that dif-
ferent substances have for heavier isotopes (e.g., the relative “preference”of liquid water for
18
O rela-
tive to the preference of vapor for
18
O). Such preferences are determined by the relative changes in
vibrational frequencies arising when heavy isotope subsitution takes place (Sharp, 2007). As stronger
chemical bonds have higher vibrational frequencies than weaker bonds, and because higher vibrational
frequencies usually correspond to larger shifts in vibrational frequencies when heavy isotope
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substitution takes place, heavier isotopes tend to partition (“fraction-
ate”) into the substance with stronger chemical bonds under thermo-
dynamic equilibrium (Chacko et al., 2001).
A resulting “rule of thumb”is “(t)he heavy isotope goes preferentially to
the chemical compound in which the element is bound most strongly”
(quoting Bigeleisen, 1965). Other qualitative guidelines characterizing
equilibrium isotopic fractionation by Schauble (2004) reviewed by Sharp
(2007) are (i) that the degree of equilibrium fractionation among two coex-
isting phases tends to increase as temperature decreases (i.e., greater iso-
topic fractionation under cooler conditions) and (ii) that equilibrium
isotopic fractionation tends to be greater for isotopes with larger percent
differences in mass. In this review paper, the most relevant equilibrium
isotopic fractionation is that defining how heavier versus lighter isotopo-
logues of H
2
O partition into liquid (i.e., water) from vapor under the
quasi‐equilibrium conditions that characterize condensation in clouds
(for empirical formulae, Horita & Wesolowski, 1994).
ii Kinetic fractionation can be important in irreversible reactions, or reversible reactions taking place under
thermodynamic disequilibrium (for texts on the topic, Allègre, 2008; White, 2013). Kinetic isotope
fractionation arises due to different reaction rates among molecules with different masses. Requisite
activation energies for a given reaction are proportional to molecular mass, meaning heavier
isotopologues tend to have higher activation energies for a given reaction and therefore react more slowly
than lighter counterparts. Further, molecular translational velocities are related inversely to molecular
mass (i.e., v
1
/v
2
=[m
2
/m
1
]
1/2
, where vis translation velocity and mis molecular mass for isotopologues
[subscripts] “1”and “2”). The ramification is that lighter isotopologues tend to diffuse faster and react
more readily than heavier isotopologues under constant conditions.
For this review paper, the most relevant kinetic isotopic fractionation is that associated with the evaporation
of soil or open water into subsaturated air. Open water evaporation proceeds under disequilibrium
conditions; that is, the rate that H
2
O
liquid
molecules evaporate exceeds the rate that H
2
O
vapor
molecules
condense on the air‐liquid interface. Evaporation encompasses both kinetic and equilibrium isotope effects,
and quantifying the combination of these two effects has been a focus of considerable experimental research
(e.g., Cappa et al., 2003; Luz et al., 2009). In practice, evaporative isotopic fractionation is often estimated
using a model (e.g., Craig & Gordon, 1965; read reviews by Gat, 2008, and Horita et al., 2008). Note, while
open water evaporation commonly proceeds under disequilibrium conditions, condensation commonly
takes place under conditions closer to thermodynamic equilibrium; therefore, the degree and types (i.e.,
equilibrium and kinetic) of isotopic fractionation involved in evaporation versus condensation commonly
differ in nature.
1.3. Stable Oxygen and Hydrogen Isotope Systematics
Oxygen has three naturally occurring isotopes (
16
O,
17
O, and
18
O); all three are stable. Hydrogen has three
naturally occurring isotopes (
1
H,
2
H, and
3
H); two are stable (
1
H and
2
H; this subsection 1.3), and one is
radioactive (
3
H; subsection 1.4). The stable isotopes
16
O(“oxygen‐16”),
18
O(“oxygen‐18”),
1
H(“protium”),
and
2
H(“deuterium”) are the most widely measured in isotope hydrogeology and are a focus of this review
(Table 1; for advances involving
17
O see S. Li, et al., 2015; S. Li, et al., 2017). Abundances of
16
O,
18
O and
1
H,
2
H are reported relative to standard seawater in “delta notation”(equations (1) and (2)):
δ18O¼
18O=16 O

sample
18O=16 O

SMOW
−1
"#
×1000‰;(1)
δ2H¼
2H=1H