Oxygen and hydrogen isotope geochemistry of thermal springs of the Western Cape, South Africa: Recharge at high altitude?

Diamond, Roger E.; Harris, Chris

doi:10.1016/s0899-5362(00)80002-0

Cited by 34 publications

(18 citation statements)

References 9 publications

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“…This is a known oversimplification (Jasechko, Wassenaar, & Mayer, ), as recharge ratios vary within individual seasons.

\frac{{((), R / P)}_{winter}}{{((), R / P)}_{summer}}

values estimated by the approach described above are best interpreted as approximations. It remains challenging to untangle the relevance of seasonally selective recharge from other factors that may also lead to low groundwater δ 18 O values relative to annual precipitation δ 18 O values, including recharge at higher elevations where precipitation δ 18 O values are often lower (e.g., Gallaher, ; Diamond & Harris, ; Weyhenmeyer et al, ; Zhao et al, ; Figure ). Strong δ 18 O P (annual) ‐elevation relationships do not exist in some of the locations where recharge biases have been proposed (e.g., Cunningham et al, ; Winograd et al, ), implying high‐elevation recharge cannot explain the observation of δ G < δ P (annual) in many areas.…”

Section: Seasonal Biases In Groundwater Rechargementioning

confidence: 99%

Global Isotope Hydrogeology―Review

Jasechko

2019

Reviews of Geophysics

213

124

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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.

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“…This is a known oversimplification (Jasechko, Wassenaar, & Mayer, ), as recharge ratios vary within individual seasons.

\frac{{((), R / P)}_{winter}}{{((), R / P)}_{summer}}

Section: Seasonal Biases In Groundwater Rechargementioning

confidence: 99%

Global Isotope Hydrogeology―Review

Jasechko

2019

Reviews of Geophysics

213

124

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“…Their study also explored the contribution of rock–fluid interactions on the original hydrochemistry of groundwater in the area. Diamond and Harris () affirmed on the basis of analysis of data of the stable isotopes of hydrogen, oxygen, and carbon that recharge to some thermal springs in the West Cape Province of South Africa may not be of recent meteoric water. In all these cases, natural tracers have proved useful in hydrological studies in the region.…”

Section: Introductionmentioning

confidence: 99%

The groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks: an application of natural environmental tracers

Yidana

Koffie

2013

Hydrological Processes

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Isotope data of precipitation and groundwater in parts of the Voltaian Basin in Northern Ghana were used to explain the groundwater recharge regime in the area. Groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area. It is therefore important to establish the processes and sources of groundwater recharge. δ18O and δ2H data for local precipitation suggest enrichment relative to the Global Meteoric Water Line (GMWL) and indicate that precipitation takes place at a relative humidity less than 100%. The groundwater data plot on an evaporation line with a slope of 5, suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone. This finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates. Groundwater recharge estimates from the chloride mass balance, CMB, method suggest recharge in the range of 1.8–32% of the annual average precipitation in the form of rainfall. The highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area. In the northern parts of the study area, groundwater recharge is lower than 12%. The recharge so computed through the application of the CMB methodology takes on a spatial distribution akin to the converse of the spatial pattern of both δ18O and δ2H in the area. As such, the locations of the highest recharge are associated with the most depleted values of the two isotopes. This observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water. The percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates. At the same time, the amount of water that finally reaches the water table is considerably reduced. Copyright © 2013 John Wiley & Sons, Ltd.

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“…Stable O and H isotopes have been widely used in tracing source of geothermal waters and delineating hydrogeochemical processes occurring in hydrothermal systems (Wilkinson et al 1992;Ghomshei and Clark 1993;Diamond and Harris 2000;Majumdar et al 2005). In the last two decades, strontium isotope analysis has also been widely applied in hydrogeochemical studies.…”

Section: Introductionmentioning

confidence: 99%

O, H, and Sr isotope evidences of mixing processes in two geothermal fluid reservoirs at Yangbajing, Tibet, China

2009

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The Yangbajing geothermal field with the highest reservoir temperature among Chinese hydrothermal systems is located about 90 km northwest to Lhasa City, capital of Tibet, where high temperature geothermal fluids occur in two reservoirs: a shallow one at a depth of 180-280 m and a deep one at 950-1,850 m. In this study, Oxygen-18 and deuterium isotope compositions as well as 87 Sr/ 86 Sr ratios of water samples collected from geothermal wells, cold springs and surface water bodies were characterized to understand the genesis of geothermal fluids at Yangbajing. The results show that the deep geothermal fluid is the mixing product of both magmatic and infiltrating snow-melt water, whereas the shallow geothermal fluid is formed by the mixing of deep geothermal fluid with cold groundwater. Using a binary mixing model with deep geothermal fluid and cold groundwater as two endmembers, the mixing ratios of the latter in most shallow geothermal water samples were calculated to be between 40 and 50%. The combined use of O, H, and Sr isotopes proves to be an effective approach to depict the major sources of geothermal fluids and the mixing processes occurring in two reservoirs at Yangbajing.Keywords Geothermal fluid Á Oxygen-18 and deuterium isotope Á 87 Sr/ 86 Sr ratio Á Mixing Á Yangbajing Á Tibet

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Oxygen and hydrogen isotope geochemistry of thermal springs of the Western Cape, South Africa: Recharge at high altitude?

Cited by 34 publications

References 9 publications

Global Isotope Hydrogeology―Review

Global Isotope Hydrogeology―Review

The groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks: an application of natural environmental tracers

O, H, and Sr isotope evidences of mixing processes in two geothermal fluid reservoirs at Yangbajing, Tibet, China

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