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Open AccessArticle

Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation

1
Department of Geosciences (retired), University of Arizona, Tucson, AZ 85721, USA
2
Laboratory of Tree Ring Research, University of Arizona, Tucson, AZ 85721, USA
*
Author to whom correspondence should be addressed.
Geosciences 2019, 9(11), 461; https://doi.org/10.3390/geosciences9110461
Received: 20 September 2019 / Revised: 24 October 2019 / Accepted: 25 October 2019 / Published: 28 October 2019
(This article belongs to the Special Issue Groundwater in arid and semiarid areas)
Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ18O and δ2H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ18O and δ2H for summer are −8.3, −53‰, and for winter, −10.8 and −70‰, respectively. Elevation-effect coefficients for δ18O and δ2H are as follows: summer, −1.6 and −7.7 ‰ per km and winter, −1.1 and −8.9 ‰ per km. Little altitude effect exists in 25% of seasons studied. At 2420 masl, amount-weighted monthly averages of δ18O and δ2H decrease in summer but increase in winter as precipitation intensity increases. In snow-banks, δ18O and δ2H commonly plots close to the winter local meteoric water line (LMWL). Four principal patterns of (δ18O, δ2H) data have been identified: (1) data plotting along LMWLs for all precipitation at >1800 masl; (2) data plotting along modified LMWLs for the wettest 30% of months at <1700 masl; (3) evaporation trends at all elevations; (4) other patterns, including those affected by ancient groundwater. Young, tritiated groundwater predominates in studied mountain blocks. Ancient groundwater forms separate systems and mixes with young groundwater. Recharge mechanisms reflect a complex interplay of precipitation season, altitude, precipitation intensity, groundwater age and geology. Tucson Basin alluvium receives mountain-front recharge containing 50%–90% winter precipitation. View Full-Text
Keywords: Arizona; New Mexico; hydrology; mountain block; recharge; stable isotopes; tritium; carbon-14 Arizona; New Mexico; hydrology; mountain block; recharge; stable isotopes; tritium; carbon-14
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Eastoe, C.J.; Wright, W.E. Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation. Geosciences 2019, 9, 461.

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