TY - JOUR
T1 - Electrical conductivity as an indicator of iron reduction rates in abiotic and biotic systems
AU - Regberg, Aaron
AU - Singha, Kamini
AU - Tien, Ming
AU - Picardal, Flynn
AU - Zheng, Quanxing
AU - Schieber, Jurgen
AU - Roden, Eric
AU - Brantley, Susan L.
PY - 2011
Y1 - 2011
N2 - Although changes in bulk electrical conductivity (b) in aquifers have been attributed to microbial activity, b 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 b increased while fluid chemistry remained constant. Growth of an electrically conductive biofilm could possibly explain this late stage b increase. The measured b 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 b 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.
AB - Although changes in bulk electrical conductivity (b) in aquifers have been attributed to microbial activity, b 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 b increased while fluid chemistry remained constant. Growth of an electrically conductive biofilm could possibly explain this late stage b increase. The measured b 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 b 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.
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U2 - 10.1029/2010WR009551
DO - 10.1029/2010WR009551
M3 - Article
AN - SCOPUS:79955050958
SN - 0043-1397
VL - 47
JO - Water Resources Research
JF - Water Resources Research
IS - 4
M1 - W04509
ER -