Analytical Expressions of Radiocarbon Distribution in Transient State Unconfined Aquifers and Their Application to Determination of Past and Present Recharges of North Africa Aquifers

Chekireb, Amine; Gonçalvès, Julio; Hamelin, Bruno; Deschamps, Pierre; Séraphin, Pierre

doi:10.1029/2021wr030018

Cited by 2 publications

(1 citation statement)

References 111 publications

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“…It was emphasized several times that the conclusions drawn on the methodology explored here is applicable only to confined aquifers. This is due to the possibility of vertical stratification of radioisotope signatures in unconfined aquifers (Chekireb et al., 2021), which would complicate this approach. Confined aquifers are a source of groundwater both in regions where unconfined aquifers are naturally limited (e.g., Meredith et al., 2012) or where depletion or pollution of shallow, unconfined aquifers has led to seeking deeper sources of useable water (e.g., M. J. Currell et al., 2012; Konikow & Kendy, 2005; Lapuyade et al., 2020).…”

Section: Discussionmentioning

confidence: 99%

Defining the Bounds of Using Radioactive Isotope Tracers to Sense Past Groundwater Recharge Under Transient State Conditions

Chmielarski

Dogramaci

Cook

et al. 2022

Geophysical Research Letters

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Analyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry.

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Section: Discussionmentioning

confidence: 99%

Defining the Bounds of Using Radioactive Isotope Tracers to Sense Past Groundwater Recharge Under Transient State Conditions

Chmielarski

Dogramaci

Cook

et al. 2022

Geophysical Research Letters

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Influence of intensive agriculture and geological heterogeneity on the recharge of an arid aquifer system (Saq–Ram, Arabian Peninsula) inferred from GRACE data

Séraphin

Gonçalvès

Hamelin

et al. 2022

Hydrol. Earth Syst. Sci.

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Abstract. This study assesses the detailed water budget of the Saq–Ram Aquifer System (520 000 km2) over the 2002–2019 period using satellite gravity data from the Gravity Recovery And Climate Experiment (GRACE). The three existing GRACE solutions were tested for their local compatibility to compute groundwater storage (GWS) variations in combination with the three soil moisture datasets available from the land surface models (LSMs) of the Global Land Data Assimilation System (GLDAS). Accounting for groundwater pumping, artificial recharge, and natural discharge uniformly distributed over the Saq–Ram domain, the GRACE-derived mass balance calculation for water yields a long-term estimate of the domain-averaged natural recharge of (2.4±1.4) mm yr−1, corresponding to (4.4±2.6) % of the annual average rainfall (AAR). Beyond the regional-scale approach proposed here, spatial heterogeneities regarding the groundwater recharge were identified. The first source of heterogeneity is of anthropogenic origin: chiefly induced by irrigation excess over irrigated surfaces (about 1 % of the domain), artificial recharge corresponds to half of the total recharge of the aquifer. The second source of recharge heterogeneity identified here is natural: volcanic lava deposits (called harrats on the Arabian Peninsula) which cover 8 % of the Saq–Ram aquifer domain but contribute to more than 50 % of the natural recharge. Hence, in addition to this application on the Arabian Peninsula, this study strongly indicates a major control of geological context on arid aquifer recharge, which has been poorly discussed hitherto. Due to large lag times of the diffuse recharge mechanism, the annual analysis using this GRACE–GLDAS approach in arid domains should be limited to areas where focused recharge is the main mechanism, while long-term analysis is valid regardless of the recharge mechanism. Moreover, it appears that about 15 years of GRACE records are required to obtain a relevant long-term recharge estimate.

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Analytical Expressions of Radiocarbon Distribution in Transient State Unconfined Aquifers and Their Application to Determination of Past and Present Recharges of North Africa Aquifers

Cited by 2 publications

References 111 publications

Defining the Bounds of Using Radioactive Isotope Tracers to Sense Past Groundwater Recharge Under Transient State Conditions

Defining the Bounds of Using Radioactive Isotope Tracers to Sense Past Groundwater Recharge Under Transient State Conditions

Influence of intensive agriculture and geological heterogeneity on the recharge of an arid aquifer system (Saq–Ram, Arabian Peninsula) inferred from GRACE data

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