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Global Isotope Hydrogeology―Review

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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.
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; 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SMOW = standard mean ocean water.
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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.
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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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... The stable isotopes of water, i.e., δ 2 H and δ 18 O and tritium ( 3 H) were analyzed using Isotope Ratio Mass Spectrometer (IRMS). The stable isotopes were calculated relative to the standard, i.e., Vienna Standard Mean Ocean Water (SMOW) [(R SAMPLE /R STANDARD )-1] and denoted as per mil (‰) (Ali, 2022;Jasechko, 2019). The Local Meteoric Water Line (LMWL) for Kabul was adopted from IAEA (http:// www. ...
... In general, the lowest values were found in deep aquifer, while the highest values were found in the shallow aquifers and surface water. This is in accordance with the earlier study carried out by Jasechko (2019). This suggests higher proportion of recharge from recent water in shallow aquifers than the deep aquifer (Ali, 2022). ...
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