High Plains groundwater isotopic composition in northeastern New Mexico (USA): relationship to recharge and hydrogeologic setting

Phan, Victoria A.; Zeigler, Kate E.; Vinson, David S.

High Plains groundwater isotopic composition in northeastern New Mexico (USA): relationship to recharge and hydrogeologic setting | Composition isotopique des eaux souterraines des Hautes Plaines au nord-est du Nouveau-Mexique (Etats-Unis d’Amérique): relations avec la recharge et les caractéristiques hydrogéologiques Composición isotópica de las aguas subterráneas de las High Plains en el noreste de New Mexico (EEUU): relación con la recarga y el marco hidrogeológico 美国新墨西哥州东北部高平原地下水的同位素组成:与补给和水文地质条件的关系 Composição isotópica da água subterrânea das Altas Planícies no nordeste do novo México (EUA): relação com a recarga e o ambiente hidrogeológico

2021

Phan, Victoria A. | Zeigler, Kate E. | Vinson, David S.

In the High Plains (HP) region of northeastern New Mexico (NE NM), USA, underlying bedrock aquifers are utilized where the High Plains Aquifer is thin, absent, or unsaturated. These usage patterns, aquifer depletion, and increasing regional aridity imply that NE NM is a possible analogy for more easterly portions of the central HP. To examine the relationship between recharge, residence time, and hydrogeologic setting, 85 well and spring samples were analyzed for environmental tracers (δD, δ¹⁸O, δ¹³C, and limited tritium and carbon-14 activities). Approximately half of the wells were open to strata of the Dakota Group. δD was −105.0 to −41.7‰ (median −58.2‰) and δ¹⁸O was −13.7 to −4.4‰ (median −8.1‰). Overall, isotopic composition is correlated with elevation and influenced by hydrogeologic setting. Ten anomalously depleted waters, most near volcanic-capped mesas, may represent higher-elevation or winter-biased recharge, a different modern precipitation source, or recharge from a cooler climate. Recharge, estimated by chloride mass balance using groundwater chloride concentrations, averages 6 mm/year below 2,000-m elevation and 16 mm/year above 2,000 m. Tritium (nondetectable to 5.7 tritium units) and carbon-14 activities (modern carbon fraction 0.23–1.05) suggest that Holocene to modern waters occur, possibly as mixtures, and that alluvial channels and other surficial features promote recharge, likely at higher rates than regional averages. It is noteworthy that isotopically depleted waters in this study tended to be tritium-free. Additional residence time tracers and seasonal precipitation isotopic sampling could address recharge and the origin of depleted waters.

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