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

Estifanos Haile, Alan E. Fryar

Research output: Contribution to journalArticlepeer-review

8 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 languageAmerican English
Pages (from-to)2403-2418
Number of pages16
JournalHydrogeology Journal
Volume25
Issue number8
DOIs
StatePublished - 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)

Fingerprint

Dive into the research topics of 'Chemical evolution of groundwater in the Wilcox aquifer of the northern Gulf Coastal Plain, USA'. Together they form a unique fingerprint.

Cite this