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Title: Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin

Abstract

Floodplains, heavily used for water supplies, housing, agriculture, mining, and industry, are important repositories of organic carbon, nutrients, and metal contaminants. The accumulation and release of these species is often mediated by redox processes. By understanding the physicochemical, hydrological, and biogeochemical controls on the distribution and variability of sediment redox conditions we can develop conceptual and numerical models of contaminant transport within floodplains. The Upper Colorado River Basin (UCRB) is impacted by former uranium and vanadium ore processing, resulting in contamination by V, Cr, Mn, As, Se, Mo and U. Previous authors have suggested that sediment redox activity occurring within organic carbon-enriched bodies located below the groundwater level may be regionally important to the maintenance and release of contaminant inventories, particularly uranium. To help assess this hypothesis, vertical distributions of Fe and S redox states and sulfide mineralogy were assessed in sediment cores from three floodplain sites spanning a 250 km transect of the central UCRB. Our results support the hypothesis that organic-enriched reduced sediments are important zones of biogeochemical activity within UCRB floodplains. Furthermore, we found that the presence of organic carbon, together with pore saturation, are the key requirements for maintaining reducing conditions, which were dominated by sulfate-reductionmore » products. Sediment texture was found to be of secondary importance and to moderate the response of the system to external forcing, such as oxidant diffusion. Consequently, fine-grain sediments are relatively resistant to oxidation in comparison to coarser-grained sediments. Exposure to oxidants consumes precipitated sulfides, with a disproportionate loss of mackinawite (FeS) as compared to the more stable pyrite. The accompanying loss of redox buffering capacity creates the potential for release of sequestered radionuclides and metals. Because of their redox reactivity and stores of metals, C, and N, organic-enriched sediments are likely to be important to nutrient and contaminant mobility within UCRB floodplain aquifers.« less

Authors:
 [1];  [2];  [3];  [1];  [2];  [4];  [1];  [4];  [5];  [1]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchroton Radiation Lightsource
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchroton Radiation Lightsource; Stanford Univ., CA (United States). Dept. of Environmental Earth System Science
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Science Lab.
  4. Stanford Univ., CA (United States). Dept. of Environmental Earth System Science
  5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); Office of Science (SC), Biological and Environmental Research (BER). Earth and Environmental Systems Science Division; USDOE Office of Legacy Management (LM); National Institutes of Health (NIH); Univ. of Michigan, Ann Arbor, MI (United States)
OSTI Identifier:
1348920
Alternate Identifier(s):
OSTI ID: 1349082; OSTI ID: 1425430; OSTI ID: 1550475
Report Number(s):
PNNL-SA-121839
Journal ID: ISSN 0048-9697; PII: S0048969717301195
Grant/Contract Number:  
AC02-76SF00515; P41GM103393; AC02-05CH11231; AC0576RL01830
Resource Type:
Accepted Manuscript
Journal Name:
Science of the Total Environment
Additional Journal Information:
Journal Volume: 603-604; Journal ID: ISSN 0048-9697
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; Floodplain sediments; Redox processes; Iron and sulfur; X-ray absorption spectroscopy; Upper Colorado River Basin

Citation Formats

Noël, Vincent, Boye, Kristin, Kukkadapu, Ravi K., Bone, Sharon, Lezama Pacheco, Juan S., Cardarelli, Emily, Janot, Noémie, Fendorf, Scott, Williams, Kenneth H., and Bargar, John R. Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin. United States: N. p., 2017. Web. doi:10.1016/j.scitotenv.2017.01.109.
Noël, Vincent, Boye, Kristin, Kukkadapu, Ravi K., Bone, Sharon, Lezama Pacheco, Juan S., Cardarelli, Emily, Janot, Noémie, Fendorf, Scott, Williams, Kenneth H., & Bargar, John R. Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin. United States. doi:10.1016/j.scitotenv.2017.01.109.
Noël, Vincent, Boye, Kristin, Kukkadapu, Ravi K., Bone, Sharon, Lezama Pacheco, Juan S., Cardarelli, Emily, Janot, Noémie, Fendorf, Scott, Williams, Kenneth H., and Bargar, John R. Fri . "Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin". United States. doi:10.1016/j.scitotenv.2017.01.109. https://www.osti.gov/servlets/purl/1348920.
@article{osti_1348920,
title = {Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin},
author = {Noël, Vincent and Boye, Kristin and Kukkadapu, Ravi K. and Bone, Sharon and Lezama Pacheco, Juan S. and Cardarelli, Emily and Janot, Noémie and Fendorf, Scott and Williams, Kenneth H. and Bargar, John R.},
abstractNote = {Floodplains, heavily used for water supplies, housing, agriculture, mining, and industry, are important repositories of organic carbon, nutrients, and metal contaminants. The accumulation and release of these species is often mediated by redox processes. By understanding the physicochemical, hydrological, and biogeochemical controls on the distribution and variability of sediment redox conditions we can develop conceptual and numerical models of contaminant transport within floodplains. The Upper Colorado River Basin (UCRB) is impacted by former uranium and vanadium ore processing, resulting in contamination by V, Cr, Mn, As, Se, Mo and U. Previous authors have suggested that sediment redox activity occurring within organic carbon-enriched bodies located below the groundwater level may be regionally important to the maintenance and release of contaminant inventories, particularly uranium. To help assess this hypothesis, vertical distributions of Fe and S redox states and sulfide mineralogy were assessed in sediment cores from three floodplain sites spanning a 250 km transect of the central UCRB. Our results support the hypothesis that organic-enriched reduced sediments are important zones of biogeochemical activity within UCRB floodplains. Furthermore, we found that the presence of organic carbon, together with pore saturation, are the key requirements for maintaining reducing conditions, which were dominated by sulfate-reduction products. Sediment texture was found to be of secondary importance and to moderate the response of the system to external forcing, such as oxidant diffusion. Consequently, fine-grain sediments are relatively resistant to oxidation in comparison to coarser-grained sediments. Exposure to oxidants consumes precipitated sulfides, with a disproportionate loss of mackinawite (FeS) as compared to the more stable pyrite. The accompanying loss of redox buffering capacity creates the potential for release of sequestered radionuclides and metals. Because of their redox reactivity and stores of metals, C, and N, organic-enriched sediments are likely to be important to nutrient and contaminant mobility within UCRB floodplain aquifers.},
doi = {10.1016/j.scitotenv.2017.01.109},
journal = {Science of the Total Environment},
number = ,
volume = 603-604,
place = {United States},
year = {2017},
month = {12}
}

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Figures / Tables:

Fig. 1 Fig. 1: Map of the Upper Colorado River Basin showing the location of the three field sites: (a) Rifle, (b) Grand Junction and (c)Naturita, CO. Profiles (left) show the distributions of particles between 1000 μm and 150 μm diameter (purple) and the particles <150 μm (green). Composition profiles (right) showmore » bulk sediment total organic carbon (OC, black) and total sulfur (S, pink) concentrations. Blue dotted lines show the minimum (Min.) and maximum (Max.) levels of groundwater table; Orange dotted lines and shading show the location of the fine- and coarse-grained NRZs. For Naturita (c), additional vertical graphs on far right-hand side give abundances of key OC described in text (ξ3.1). Unsaturated OEZ = OEZ permanently located above the water table level; Fine-grained NRZ = NRZ enriched in fine particles (<150 μm) compared to surrounding sediments; Coarse-grained NRZ= NRZ with same distribution of grain sizes as surrounding sediments (cf., Table 1). Images from http://aspenjournalism.org/2014/03/30/snowpack-and-runoff-potential-looking-good/ and http://www.nationsonline.org/oneworld/usa_map.htm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)« less

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