Electrical conductivity as an indicator of iron reduction rates in abiotic and biotic systems
Article first published online: 16 APR 2011
Copyright 2011 by the American Geophysical Union.
Water Resources Research
Volume 47, Issue 4, April 2011
How to Cite
2011), Electrical conductivity as an indicator of iron reduction rates in abiotic and biotic systems, Water Resour. Res., 47, W04509, doi:10.1029/2010WR009551., , , , , , , and (
- Issue published online: 16 APR 2011
- Article first published online: 16 APR 2011
- Manuscript Accepted: 20 DEC 2010
- Manuscript Revised: 26 NOV 2010
- Manuscript Received: 17 MAY 2010
- electrical conductivity;
- iron reduction
 Although changes in bulk electrical conductivity (σb) in aquifers have been attributed to microbial activity, σb has never been used to infer biogeochemical reaction rates quantitatively. To explore the use of electrical conductivity to measure reaction rates, we conducted iron oxide reduction experiments of increasing biological complexity. To quantify reaction rates, we propose composite reactions that incorporate the stoichiometry of five different types of reactions: redox, acid-base, sorption, dissolution/precipitation, and biosynthesis. In batch experiments and the early stages of a column experiment, such reaction stoichiometries inferred from a few chemical measurements allowed quantification of the Fe oxide reduction rate based on changes in electrical conductivity. The relationship between electrical conductivity and fluid chemistry did not hold during the latter stages of the column experiment when σb increased while fluid chemistry remained constant. Growth of an electrically conductive biofilm could possibly explain this late stage σb increase. The measured σb increase is consistent with a model proposed by analogy from percolation theory that attributes the increased conductivity to growth of biofilms with conductivity of ∼5.5 S m−1 in at least 3% of the column pore space. This work demonstrates that measurements of σb and flow rate, combined with a few direct chemical measurements, can be used to quantify biogeochemical reaction rates in controlled laboratory situations and may be able to detect the presence of biofilms. This approach may help in designing future field experiments to interpret biogeochemical reactivity from conductivity measurements.