Uranium delivery and uptake in a montane wetland, north-central Colorado, USA

Applied Geochemistry
By: , and 

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Abstract

Comprehensive sampling of peat, underlying lakebed sediments, and coexisting waters of a naturally uraniferous montane wetland are combined with hydrologic measurements to define the important controls on uranium (U) supply and uptake. The major source of U to the wetland is groundwater flowing through locally fractured and faulted granite gneiss of Proterozoic age. Dissolved U concentrations in four springs and one seep ranged from 20 to 83 ppb (μg/l). Maximum U concentrations are ∼300 ppm (mg/kg) in lakebed sediments and >3000 ppm in peat. Uranium in lakebed sediments is primarily stratabound in the more organic-rich layers, but samples of similar organic content display variable U concentrations. Post-depositional modifications include variable additions of U delivered by groundwater. Uranium distribution in peat is heterogeneous and primarily controlled by proximity to groundwater-fed springs and seeps that act as local point sources of U, and by proximity to groundwater directed along the peat/lakebeds contact. Uranium is initially sorbed on various organic components of peat as oxidized U(VI) present in groundwater. Selective extractions indicate that the majority of sorbed U remains as the oxidized species despite reducing conditions that should favor formation of U(IV). Possible explanations are kinetic hindrances related to strong complex formation between uranyl and humic substances, inhibition of anaerobic bacterial activity by low supply of dissolved iron and sulfate, and by cold temperatures.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Uranium delivery and uptake in a montane wetland, north-central Colorado, USA
Series title Applied Geochemistry
DOI 10.1016/j.apgeochem.2017.01.001
Volume 78
Issue 3
Year Published 2017
Language English
Publisher Elsevier
Contributing office(s) Geosciences and Environmental Change Science Center
Description 17 p.
First page 363
Last page 379
Country United States
State Colorado