Chemical evolution of groundwater in the Wilcox aquifer of the northern Gulf Coastal Plain, USA

Estifanos Haile; Alan E. Fryar

doi:10.1007/s10040-017-1608-y

Chemical evolution of groundwater in the Wilcox aquifer of the northern Gulf Coastal Plain, USA

Estifanos Haile, Alan E. Fryar

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

10 Scopus citations

Abstract

The Wilcox aquifer is a major groundwater resource in the northern Gulf Coastal Plain (lower Mississippi Valley) of the USA, yet the processes controlling water chemistry in this clastic aquifer have received relatively little attention. The current study combines analyses of solutes and stable isotopes in groundwater, petrography of core samples, and geochemical modeling to identify plausible reactions along a regional flow path ∼300 km long. The hydrochemical facies evolves from Ca-HCO₃ upgradient to Na-HCO₃ downgradient, with a sequential zonation of terminal electron-accepting processes from Fe(III) reduction through SO₄ ²⁻ reduction to methanogenesis. In particular, decreasing SO₄ ²⁻ and increasing δ³⁴S of SO₄ ²⁻ along the flow path, as well as observations of authigenic pyrite in core samples, provide evidence of SO₄ ²⁻ reduction. Values of δ¹³C in groundwater suggest that dissolved inorganic carbon is contributed both by oxidation of sedimentary organic matter and calcite dissolution. Inverse modeling identified multiple plausible sets of reactions between sampled wells, which typically involved cation exchange, pyrite precipitation, CH₂O oxidation, and dissolution of amorphous Fe(OH)₃, calcite, or siderite. These reactions are consistent with processes identified in previous studies of Atlantic Coastal Plain aquifers. Contrasts in groundwater chemistry between the Wilcox and the underlying McNairy and overlying Claiborne aquifers indicate that confining units are relatively effective in limiting cross-formational flow, but localized cross-formational mixing could occur via fault zones. Consequently, increased pumping in the vicinity of fault zones could facilitate upward movement of saline water into the Wilcox.

Original language	American English
Pages (from-to)	2403-2418
Number of pages	16
Journal	Hydrogeology Journal
Volume	25
Issue number	8
DOIs	https://doi.org/10.1007/s10040-017-1608-y
State	Published - Dec 1 2017

Bibliographical note

Funding Information:
Acknowledgements This work was supported by US Geological Survey grant number 06HQGR0087 to the authors through the University of Kentucky and by a student research grant to E. Haile from the Gulf Coast Association of Geological Societies. The authors thank operators of municipal wells and the Arkansas Geological Survey for facilitating sampling; Tricia Coakley, Elisa D’Angelo, Millie Hamilton, John May, and Marty Parris for assistance with analyses; and Ed Woolery for providing Fig. 1a. The views and conclusions contained herein are those of the authors and do not necessarily represent the official policies, either expressed or implied, of the US Government.

Funding Information:
This work was supported by US Geological Survey grant number 06HQGR0087 to the authors through the University of Kentucky and by a student research grant to E. Haile from the Gulf Coast Association of Geological Societies. The authors thank operators of municipal wells and the Arkansas Geological Survey for facilitating sampling; Tricia Coakley, Elisa D?Angelo, Millie Hamilton, John May, and Marty Parris for assistance with analyses; and Ed Woolery for providing Fig. 1 a. The views and conclusions contained herein are those of the authors and do not necessarily represent the official policies, either expressed or implied, of the US Government.

Publisher Copyright:
© 2017, Springer-Verlag Berlin Heidelberg.

Keywords

Groundwater monitoring
Hydrochemical modeling
Hydrogeochemistry
USA

ASJC Scopus subject areas

Water Science and Technology
Earth and Planetary Sciences (miscellaneous)

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10.1007/s10040-017-1608-y

Cite this

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title = "Chemical evolution of groundwater in the Wilcox aquifer of the northern Gulf Coastal Plain, USA",

abstract = "The Wilcox aquifer is a major groundwater resource in the northern Gulf Coastal Plain (lower Mississippi Valley) of the USA, yet the processes controlling water chemistry in this clastic aquifer have received relatively little attention. The current study combines analyses of solutes and stable isotopes in groundwater, petrography of core samples, and geochemical modeling to identify plausible reactions along a regional flow path ∼300 km long. The hydrochemical facies evolves from Ca-HCO3 upgradient to Na-HCO3 downgradient, with a sequential zonation of terminal electron-accepting processes from Fe(III) reduction through SO4 2− reduction to methanogenesis. In particular, decreasing SO4 2− and increasing δ34S of SO4 2− along the flow path, as well as observations of authigenic pyrite in core samples, provide evidence of SO4 2− reduction. Values of δ13C in groundwater suggest that dissolved inorganic carbon is contributed both by oxidation of sedimentary organic matter and calcite dissolution. Inverse modeling identified multiple plausible sets of reactions between sampled wells, which typically involved cation exchange, pyrite precipitation, CH2O oxidation, and dissolution of amorphous Fe(OH)3, calcite, or siderite. These reactions are consistent with processes identified in previous studies of Atlantic Coastal Plain aquifers. Contrasts in groundwater chemistry between the Wilcox and the underlying McNairy and overlying Claiborne aquifers indicate that confining units are relatively effective in limiting cross-formational flow, but localized cross-formational mixing could occur via fault zones. Consequently, increased pumping in the vicinity of fault zones could facilitate upward movement of saline water into the Wilcox.",

keywords = "Groundwater monitoring, Hydrochemical modeling, Hydrogeochemistry, USA",

author = "Estifanos Haile and Fryar, {Alan E.}",

note = "Funding Information: Acknowledgements This work was supported by US Geological Survey grant number 06HQGR0087 to the authors through the University of Kentucky and by a student research grant to E. Haile from the Gulf Coast Association of Geological Societies. The authors thank operators of municipal wells and the Arkansas Geological Survey for facilitating sampling; Tricia Coakley, Elisa D{\textquoteright}Angelo, Millie Hamilton, John May, and Marty Parris for assistance with analyses; and Ed Woolery for providing Fig. 1a. The views and conclusions contained herein are those of the authors and do not necessarily represent the official policies, either expressed or implied, of the US Government. Funding Information: This work was supported by US Geological Survey grant number 06HQGR0087 to the authors through the University of Kentucky and by a student research grant to E. Haile from the Gulf Coast Association of Geological Societies. The authors thank operators of municipal wells and the Arkansas Geological Survey for facilitating sampling; Tricia Coakley, Elisa D?Angelo, Millie Hamilton, John May, and Marty Parris for assistance with analyses; and Ed Woolery for providing Fig. 1 a. The views and conclusions contained herein are those of the authors and do not necessarily represent the official policies, either expressed or implied, of the US Government. Publisher Copyright: {\textcopyright} 2017, Springer-Verlag Berlin Heidelberg.",

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doi = "10.1007/s10040-017-1608-y",

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N2 - The Wilcox aquifer is a major groundwater resource in the northern Gulf Coastal Plain (lower Mississippi Valley) of the USA, yet the processes controlling water chemistry in this clastic aquifer have received relatively little attention. The current study combines analyses of solutes and stable isotopes in groundwater, petrography of core samples, and geochemical modeling to identify plausible reactions along a regional flow path ∼300 km long. The hydrochemical facies evolves from Ca-HCO3 upgradient to Na-HCO3 downgradient, with a sequential zonation of terminal electron-accepting processes from Fe(III) reduction through SO4 2− reduction to methanogenesis. In particular, decreasing SO4 2− and increasing δ34S of SO4 2− along the flow path, as well as observations of authigenic pyrite in core samples, provide evidence of SO4 2− reduction. Values of δ13C in groundwater suggest that dissolved inorganic carbon is contributed both by oxidation of sedimentary organic matter and calcite dissolution. Inverse modeling identified multiple plausible sets of reactions between sampled wells, which typically involved cation exchange, pyrite precipitation, CH2O oxidation, and dissolution of amorphous Fe(OH)3, calcite, or siderite. These reactions are consistent with processes identified in previous studies of Atlantic Coastal Plain aquifers. Contrasts in groundwater chemistry between the Wilcox and the underlying McNairy and overlying Claiborne aquifers indicate that confining units are relatively effective in limiting cross-formational flow, but localized cross-formational mixing could occur via fault zones. Consequently, increased pumping in the vicinity of fault zones could facilitate upward movement of saline water into the Wilcox.

AB - The Wilcox aquifer is a major groundwater resource in the northern Gulf Coastal Plain (lower Mississippi Valley) of the USA, yet the processes controlling water chemistry in this clastic aquifer have received relatively little attention. The current study combines analyses of solutes and stable isotopes in groundwater, petrography of core samples, and geochemical modeling to identify plausible reactions along a regional flow path ∼300 km long. The hydrochemical facies evolves from Ca-HCO3 upgradient to Na-HCO3 downgradient, with a sequential zonation of terminal electron-accepting processes from Fe(III) reduction through SO4 2− reduction to methanogenesis. In particular, decreasing SO4 2− and increasing δ34S of SO4 2− along the flow path, as well as observations of authigenic pyrite in core samples, provide evidence of SO4 2− reduction. Values of δ13C in groundwater suggest that dissolved inorganic carbon is contributed both by oxidation of sedimentary organic matter and calcite dissolution. Inverse modeling identified multiple plausible sets of reactions between sampled wells, which typically involved cation exchange, pyrite precipitation, CH2O oxidation, and dissolution of amorphous Fe(OH)3, calcite, or siderite. These reactions are consistent with processes identified in previous studies of Atlantic Coastal Plain aquifers. Contrasts in groundwater chemistry between the Wilcox and the underlying McNairy and overlying Claiborne aquifers indicate that confining units are relatively effective in limiting cross-formational flow, but localized cross-formational mixing could occur via fault zones. Consequently, increased pumping in the vicinity of fault zones could facilitate upward movement of saline water into the Wilcox.

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Chemical evolution of groundwater in the Wilcox aquifer of the northern Gulf Coastal Plain, USA

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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