Characterizing U-series Isotope Signatures in Soils and Headwater Streams in a Complex Volcanic Terrain: Jemez River Critical Zone Observatory, Valles Caldera, NM.

Persistent Link:
http://hdl.handle.net/10150/305863
Title:
Characterizing U-series Isotope Signatures in Soils and Headwater Streams in a Complex Volcanic Terrain: Jemez River Critical Zone Observatory, Valles Caldera, NM.
Author:
Huckle, David Martyn
Issue Date:
2013
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Uranium-series isotopes are an emerging tool to characterize weathering and soil forming processes in the Critical Zone, the dynamic region of earth's surface where bedrock, water, soil, and life chemically and physically interact to support ecosystems. Understanding controls on the U-series composition of soils across a range of lithologies and climate is critical to applying existing mass balance models of U-series isotopes to calculate soil formation rates in these systems. This study seeks to understand the behavior of U-series isotopes in soil profiles in the semi-arid complex volcanic terrain of the Valles Caldera, NM. (²³⁴U/²³⁸U) measured in soils ranged from 0.90 to 1.56 and (²³⁰Th/²³⁸U) values ranged from 0.48 to 1.39. Significant ²³⁰Th enrichment in upper soil profiles was interpreted as evidence of mixing with ²³⁰Th-enriched volcanic ash and significant ²³⁴U enrichment in one soil profile was interpreted as evidence of addition of U to soils from ²³⁴U-enriched soil solutions. A simple U isotope mass balance model was applied to estimate soil residence time based on U addition, which yielded a minimum residence time of ~10ka. Evidence of past episodic mixing of volcanic ash in these soils suggests modeling soil formation using a mass balance approach is problematic, and future applications of existing models in other heterogeneous volcanic soils should be applied cautiously. U-series isotopes have also shown promise as a tracer of residence time in shallow groundwater and streams. In this study, (²³⁴U/²³⁸U) in dissolved U is used to trace seasonal variation in source water contributions to streamflow in a small (3.29km²), headwater catchment in the Jemez River Basin Critical Zone Observatory within the Valles Caldera. Systematically lower (²³⁴U/²³⁸U) values in dissolved U were observed in spring and stream waters in conjunction with greater contributions of longer residence time waters during snowmelt ((²³⁴U/²³⁸U) ranged 1.7 to 2.8) vs. dry seasons ((²³⁴U/²³⁸U) ranged 1.9 to 3.1). The lower (²³⁴U/²³⁸U) values in longer residence time waters were attributed to progressive depletion of easily-weathered ²³⁴U with increasing duration of water rock interaction. Further studies with more quantitative age tracers, such as ³H, could help to establish (²³⁴U/²³⁸U) values as a powerful tracer of water sources and residence time in streamwaters at the catchment scale.
Type:
text; Electronic Thesis
Keywords:
Isotope Geochemistry; U-series Isotopes; Hydrology
Degree Name:
M.S.
Degree Level:
masters
Degree Program:
Graduate College; Hydrology
Degree Grantor:
University of Arizona
Advisor:
McIntosh, Jennifer

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleCharacterizing U-series Isotope Signatures in Soils and Headwater Streams in a Complex Volcanic Terrain: Jemez River Critical Zone Observatory, Valles Caldera, NM.en_US
dc.creatorHuckle, David Martynen_US
dc.contributor.authorHuckle, David Martynen_US
dc.date.issued2013-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractUranium-series isotopes are an emerging tool to characterize weathering and soil forming processes in the Critical Zone, the dynamic region of earth's surface where bedrock, water, soil, and life chemically and physically interact to support ecosystems. Understanding controls on the U-series composition of soils across a range of lithologies and climate is critical to applying existing mass balance models of U-series isotopes to calculate soil formation rates in these systems. This study seeks to understand the behavior of U-series isotopes in soil profiles in the semi-arid complex volcanic terrain of the Valles Caldera, NM. (²³⁴U/²³⁸U) measured in soils ranged from 0.90 to 1.56 and (²³⁰Th/²³⁸U) values ranged from 0.48 to 1.39. Significant ²³⁰Th enrichment in upper soil profiles was interpreted as evidence of mixing with ²³⁰Th-enriched volcanic ash and significant ²³⁴U enrichment in one soil profile was interpreted as evidence of addition of U to soils from ²³⁴U-enriched soil solutions. A simple U isotope mass balance model was applied to estimate soil residence time based on U addition, which yielded a minimum residence time of ~10ka. Evidence of past episodic mixing of volcanic ash in these soils suggests modeling soil formation using a mass balance approach is problematic, and future applications of existing models in other heterogeneous volcanic soils should be applied cautiously. U-series isotopes have also shown promise as a tracer of residence time in shallow groundwater and streams. In this study, (²³⁴U/²³⁸U) in dissolved U is used to trace seasonal variation in source water contributions to streamflow in a small (3.29km²), headwater catchment in the Jemez River Basin Critical Zone Observatory within the Valles Caldera. Systematically lower (²³⁴U/²³⁸U) values in dissolved U were observed in spring and stream waters in conjunction with greater contributions of longer residence time waters during snowmelt ((²³⁴U/²³⁸U) ranged 1.7 to 2.8) vs. dry seasons ((²³⁴U/²³⁸U) ranged 1.9 to 3.1). The lower (²³⁴U/²³⁸U) values in longer residence time waters were attributed to progressive depletion of easily-weathered ²³⁴U with increasing duration of water rock interaction. Further studies with more quantitative age tracers, such as ³H, could help to establish (²³⁴U/²³⁸U) values as a powerful tracer of water sources and residence time in streamwaters at the catchment scale.en_US
dc.typetexten_US
dc.typeElectronic Thesisen_US
dc.subjectIsotope Geochemistryen_US
dc.subjectU-series Isotopesen_US
dc.subjectHydrologyen_US
thesis.degree.nameM.S.en_US
thesis.degree.levelmastersen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineHydrologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorMcIntosh, Jenniferen_US
dc.contributor.committeememberMa, Linen_US
dc.contributor.committeememberChorover, Jonen_US
dc.contributor.committeememberRasmussen, Craigen_US
dc.contributor.committeememberMeixner, Thomasen_US
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