Lithologic and redox controls on hexavalent chromium in vadose zone sediments of California's Central Valley

Cynthia N. McClain; Scott Fendorf; Shane T. Johnson; Alana Menendez; Kate Maher

doi:10.1016/j.gca.2019.07.044

Lithologic and redox controls on hexavalent chromium in vadose zone sediments of California's Central Valley

Cynthia N. McClain, Scott Fendorf, Shane T. Johnson, Alana Menendez, Kate Maher

Continental Scientific Drilling Facility

Research output: Contribution to journal › Article › peer-review

21 Scopus citations

Abstract

In agricultural regions of California where ultramafic sediments containing naturally occurring Cr(III) are present, correlations between Cr(VI) and nitrate in groundwater have been attributed to oxidation of Cr(III) in vadose sediments and mobilization by areal recharge, including irrigation return. However, the distribution of Cr and nitrate through the vadose zone have yet to be evaluated together to investigate the controls on geogenic Cr(VI) occurrence and resulting Cr(VI) production rates and export fluxes to groundwater. To develop a framework for evaluating geogenic Cr(VI) contamination, we analyze vadose zone sediment cores from the southwestern Sacramento Valley of California at high spatial resolution. In the sandy, oxic, ultramafic, Cr-rich Holocene alluvial sediment, Cr(III) is oxidized to Cr(VI), resulting in increasing Cr(VI) concentrations with depth up to 79 μg/kg. Oxidation is likely associated with μ-meter scale co-located Mn(IV)-oxides. Within the fine-grained Pleistocene sediments beneath the historic high water table (5–18 m), Cr(VI) concentrations decrease with depth to <30 μg/kg due to subsequent reduction. Patterns in Cr(VI) concentration parallel nitrate due to the similar depth of production zones, oxidation-reduction potential and geochemical behavior. Field evidence in the shallow profile also supports Cr(VI) production by enhanced Cr(III) dissolution due to nitrification-induced acidification and subsequent oxidation by Mn-oxides. From Cr(VI) and nitrate concentration gradients with depth through the vadose zone (∼20 m), we calculate field-based net production and removal rates, quantify vadose zone storage (156–1168 kg Cr(VI)/km²; 1 × 10⁵–2.6 × 10⁵ kg N/km²), and estimate export fluxes to groundwater (40–1314 kg Cr(VI)/km²/yr; 5–487 kg N/km²/yr). The framework we present for evaluating vadose zone geogenic Cr(VI) contamination highlights the compounding effects that vadose zone lithology and hydrology can have on solute production, accumulation, development of redoxclines, and subsequent distribution of redox sensitive elements in alluvial sediment and groundwater.

Original language	English (US)
Pages (from-to)	478-494
Number of pages	17
Journal	Geochimica et Cosmochimica Acta
Volume	265
DOIs	https://doi.org/10.1016/j.gca.2019.07.044
State	Published - Nov 15 2019

Bibliographical note

Funding Information:
This work was supported by the U.S. National Science Foundation (Graduate Research Fellowship DGE-114747 to C.N. McClain, and EAR-1254156 to K. Maher), Stanford University’s McGee Grant and Stanford University’s School of Earth Summer Undergraduate Research Program. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Cores are archived at LacCore (National Lacustrine Core Facility), Department of Earth Sciences, University of Minnesota-Twin Cities. We thank Dr. Guangchao Li, Doug Turner, Dr. Samuel M. Webb, Dr. Juan Lezama Pacheco, Bob Devany, Mary Stallard, Bill McIlvride, and Rob Davis for assistance and fruitful conversations in the field and laboratory. Appendix A

Publisher Copyright:
© 2019

Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.

Keywords

California
Chromium
Groundwater
Nitrate
Sediments
Vadose zone

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UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1016/j.gca.2019.07.044

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title = "Lithologic and redox controls on hexavalent chromium in vadose zone sediments of California's Central Valley",

abstract = "In agricultural regions of California where ultramafic sediments containing naturally occurring Cr(III) are present, correlations between Cr(VI) and nitrate in groundwater have been attributed to oxidation of Cr(III) in vadose sediments and mobilization by areal recharge, including irrigation return. However, the distribution of Cr and nitrate through the vadose zone have yet to be evaluated together to investigate the controls on geogenic Cr(VI) occurrence and resulting Cr(VI) production rates and export fluxes to groundwater. To develop a framework for evaluating geogenic Cr(VI) contamination, we analyze vadose zone sediment cores from the southwestern Sacramento Valley of California at high spatial resolution. In the sandy, oxic, ultramafic, Cr-rich Holocene alluvial sediment, Cr(III) is oxidized to Cr(VI), resulting in increasing Cr(VI) concentrations with depth up to 79 μg/kg. Oxidation is likely associated with μ-meter scale co-located Mn(IV)-oxides. Within the fine-grained Pleistocene sediments beneath the historic high water table (5–18 m), Cr(VI) concentrations decrease with depth to <30 μg/kg due to subsequent reduction. Patterns in Cr(VI) concentration parallel nitrate due to the similar depth of production zones, oxidation-reduction potential and geochemical behavior. Field evidence in the shallow profile also supports Cr(VI) production by enhanced Cr(III) dissolution due to nitrification-induced acidification and subsequent oxidation by Mn-oxides. From Cr(VI) and nitrate concentration gradients with depth through the vadose zone (∼20 m), we calculate field-based net production and removal rates, quantify vadose zone storage (156–1168 kg Cr(VI)/km2; 1 × 105–2.6 × 105 kg N/km2), and estimate export fluxes to groundwater (40–1314 kg Cr(VI)/km2/yr; 5–487 kg N/km2/yr). The framework we present for evaluating vadose zone geogenic Cr(VI) contamination highlights the compounding effects that vadose zone lithology and hydrology can have on solute production, accumulation, development of redoxclines, and subsequent distribution of redox sensitive elements in alluvial sediment and groundwater.",

keywords = "California, Chromium, Groundwater, Nitrate, Sediments, Vadose zone",

author = "McClain, {Cynthia N.} and Scott Fendorf and Johnson, {Shane T.} and Alana Menendez and Kate Maher",

note = "Funding Information: This work was supported by the U.S. National Science Foundation (Graduate Research Fellowship DGE-114747 to C.N. McClain, and EAR-1254156 to K. Maher), Stanford University{\textquoteright}s McGee Grant and Stanford University{\textquoteright}s School of Earth Summer Undergraduate Research Program. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Cores are archived at LacCore (National Lacustrine Core Facility), Department of Earth Sciences, University of Minnesota-Twin Cities. We thank Dr. Guangchao Li, Doug Turner, Dr. Samuel M. Webb, Dr. Juan Lezama Pacheco, Bob Devany, Mary Stallard, Bill McIlvride, and Rob Davis for assistance and fruitful conversations in the field and laboratory. Appendix A Publisher Copyright: {\textcopyright} 2019 Copyright: Copyright 2019 Elsevier B.V., All rights reserved.",

year = "2019",

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doi = "10.1016/j.gca.2019.07.044",

language = "English (US)",

volume = "265",

pages = "478--494",

journal = "Geochimica et Cosmochimica Acta",

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TY - JOUR

T1 - Lithologic and redox controls on hexavalent chromium in vadose zone sediments of California's Central Valley

AU - McClain, Cynthia N.

AU - Fendorf, Scott

AU - Johnson, Shane T.

AU - Menendez, Alana

AU - Maher, Kate

N1 - Funding Information: This work was supported by the U.S. National Science Foundation (Graduate Research Fellowship DGE-114747 to C.N. McClain, and EAR-1254156 to K. Maher), Stanford University’s McGee Grant and Stanford University’s School of Earth Summer Undergraduate Research Program. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Cores are archived at LacCore (National Lacustrine Core Facility), Department of Earth Sciences, University of Minnesota-Twin Cities. We thank Dr. Guangchao Li, Doug Turner, Dr. Samuel M. Webb, Dr. Juan Lezama Pacheco, Bob Devany, Mary Stallard, Bill McIlvride, and Rob Davis for assistance and fruitful conversations in the field and laboratory. Appendix A Publisher Copyright: © 2019 Copyright: Copyright 2019 Elsevier B.V., All rights reserved.

PY - 2019/11/15

Y1 - 2019/11/15

N2 - In agricultural regions of California where ultramafic sediments containing naturally occurring Cr(III) are present, correlations between Cr(VI) and nitrate in groundwater have been attributed to oxidation of Cr(III) in vadose sediments and mobilization by areal recharge, including irrigation return. However, the distribution of Cr and nitrate through the vadose zone have yet to be evaluated together to investigate the controls on geogenic Cr(VI) occurrence and resulting Cr(VI) production rates and export fluxes to groundwater. To develop a framework for evaluating geogenic Cr(VI) contamination, we analyze vadose zone sediment cores from the southwestern Sacramento Valley of California at high spatial resolution. In the sandy, oxic, ultramafic, Cr-rich Holocene alluvial sediment, Cr(III) is oxidized to Cr(VI), resulting in increasing Cr(VI) concentrations with depth up to 79 μg/kg. Oxidation is likely associated with μ-meter scale co-located Mn(IV)-oxides. Within the fine-grained Pleistocene sediments beneath the historic high water table (5–18 m), Cr(VI) concentrations decrease with depth to <30 μg/kg due to subsequent reduction. Patterns in Cr(VI) concentration parallel nitrate due to the similar depth of production zones, oxidation-reduction potential and geochemical behavior. Field evidence in the shallow profile also supports Cr(VI) production by enhanced Cr(III) dissolution due to nitrification-induced acidification and subsequent oxidation by Mn-oxides. From Cr(VI) and nitrate concentration gradients with depth through the vadose zone (∼20 m), we calculate field-based net production and removal rates, quantify vadose zone storage (156–1168 kg Cr(VI)/km2; 1 × 105–2.6 × 105 kg N/km2), and estimate export fluxes to groundwater (40–1314 kg Cr(VI)/km2/yr; 5–487 kg N/km2/yr). The framework we present for evaluating vadose zone geogenic Cr(VI) contamination highlights the compounding effects that vadose zone lithology and hydrology can have on solute production, accumulation, development of redoxclines, and subsequent distribution of redox sensitive elements in alluvial sediment and groundwater.

AB - In agricultural regions of California where ultramafic sediments containing naturally occurring Cr(III) are present, correlations between Cr(VI) and nitrate in groundwater have been attributed to oxidation of Cr(III) in vadose sediments and mobilization by areal recharge, including irrigation return. However, the distribution of Cr and nitrate through the vadose zone have yet to be evaluated together to investigate the controls on geogenic Cr(VI) occurrence and resulting Cr(VI) production rates and export fluxes to groundwater. To develop a framework for evaluating geogenic Cr(VI) contamination, we analyze vadose zone sediment cores from the southwestern Sacramento Valley of California at high spatial resolution. In the sandy, oxic, ultramafic, Cr-rich Holocene alluvial sediment, Cr(III) is oxidized to Cr(VI), resulting in increasing Cr(VI) concentrations with depth up to 79 μg/kg. Oxidation is likely associated with μ-meter scale co-located Mn(IV)-oxides. Within the fine-grained Pleistocene sediments beneath the historic high water table (5–18 m), Cr(VI) concentrations decrease with depth to <30 μg/kg due to subsequent reduction. Patterns in Cr(VI) concentration parallel nitrate due to the similar depth of production zones, oxidation-reduction potential and geochemical behavior. Field evidence in the shallow profile also supports Cr(VI) production by enhanced Cr(III) dissolution due to nitrification-induced acidification and subsequent oxidation by Mn-oxides. From Cr(VI) and nitrate concentration gradients with depth through the vadose zone (∼20 m), we calculate field-based net production and removal rates, quantify vadose zone storage (156–1168 kg Cr(VI)/km2; 1 × 105–2.6 × 105 kg N/km2), and estimate export fluxes to groundwater (40–1314 kg Cr(VI)/km2/yr; 5–487 kg N/km2/yr). The framework we present for evaluating vadose zone geogenic Cr(VI) contamination highlights the compounding effects that vadose zone lithology and hydrology can have on solute production, accumulation, development of redoxclines, and subsequent distribution of redox sensitive elements in alluvial sediment and groundwater.

KW - California

KW - Chromium

KW - Groundwater

KW - Nitrate

KW - Sediments

KW - Vadose zone

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M3 - Article

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SN - 0016-7037

VL - 265

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JO - Geochimica et Cosmochimica Acta

JF - Geochimica et Cosmochimica Acta

ER -

Lithologic and redox controls on hexavalent chromium in vadose zone sediments of California's Central Valley

Abstract

Bibliographical note

Keywords

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UN SDGs

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