Thermal intensification of microbial Fe(II)/Fe(III) redox cycling in a pristine shallow sand aquifer on the Canadian Shield

Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved..

This investigation evaluates spatial relationships between summer (July) groundwater temperatures and Fe(II)/Fe(III) biogeochemical cycling over a five year period in a shallow pristine sand aquifer at Meilleurs Bay near Deep River, Ontario, Canada. A warm subsurface thermal island of 12.5-16.1 °C, compared to background conditions of 10-11 °C, was manifest in contour maps of average groundwater temperature over the study period. The warm zone coincided with an area of convergent groundwater flow, implicating horizontal heat transfer by advective convection as the reason for elevated temperatures. Additionally, high concentrations of dissolved Fe(II) and Fe(III) overlapped the warm thermal island, indicative of increased rates of bacterial Fe(II)-oxidation and Fe(III)-reduction. A depletion in the modal abundance of Fe(II)-bearing minerals, notably amphibole and biotite, inside the area of the warm thermal island was also observed, suggesting enhanced mineral dissolution owing to chemoautotrophic Fe(II)-oxidation coupled to the reduction and fixation of dissolved inorganic carbon as biomass. Throughout the aquifer, redox conditions were poised in terms of Eh and pH close to equilibrium with respect to the Fe(II)/Fe(OH)3 couple, feasibly enabling simultaneous bacterial Fe(II)-oxidation and Fe(III)-reduction with an adequate supply of electron acceptors and donors, respectively. The significance of higher groundwater temperature as a determinant of elevated dissolved Fe(II) and Fe(III) concentrations induced by thermal intensification of microbial biogeochemical activities yielded Pearson product-moment correlations in which temperature alone, as a single independent variable, explains almost 30 to nearly 60 percent of the variation in the measured dissolved Fe(II) and Fe(III) concentrations in the groundwater. These results emphasize the important influence of thermal conditions on biogeochemical processes in aquifers coupled to the development of steep gradients in groundwater quality over short distances in shallow unconfined groundwater systems.

Medienart:

E-Artikel

Erscheinungsjahr:

2016

Erschienen:

2016

Enthalten in:

Zur Gesamtaufnahme - volume:106

Enthalten in:

Water research - 106(2016) vom: 01. Dez., Seite 604-612

Sprache:

Englisch

Beteiligte Personen:

Shirokova, V L [VerfasserIn]
Enright, A M L [VerfasserIn]
Kennedy, C B [VerfasserIn]
Ferris, F G [VerfasserIn]

Links:

Volltext

Themen:

Bacterial
Biogeochemical cycling
Fe(II)/Fe(III)
Ferric Compounds
Ferrous Compounds
Groundwater
Journal Article
Mineral weathering
Oxidation-reduction
Temperature
Water Pollutants, Chemical

Anmerkungen:

Date Completed 04.05.2017

Date Revised 04.09.2017

published: Print-Electronic

Citation Status MEDLINE

doi:

10.1016/j.watres.2016.10.050

funding:

Förderinstitution / Projekttitel:

PPN (Katalog-ID):

NLM265640857