Redox-network reconfiguration inferred from the ln[O2]–Eh relationship under mixed-potential conditions in a shallow pond time series
- 1Department of Chemistry, Biology, and Environmental Sciences, Nara Women’s University, Kita-Uoya Nishimachi, Nara 630-8506, Japan
- 2Environmental Conservation Division, Environmental and Fundamental Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan
- 3Department of Environmental and Natural Resource Sciences, Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu-shi, Tokyo 183-8509, Japan
Abstract
Oxidation–reduction potential (Eh) is widely used as an in situ indicator of redox conditions in aquatic environments, and field electrodes typically record a mixed potential generated by multiple concurrent interfacial redox reactions. Beyond a simple Nernstian interpretation based on a single redox couple, here we ask what mechanistic information can be extracted from an observed relationship between Eh and a single chemical species under mixed-potential conditions, focusing on dissolved oxygen. Using a linearized mixed-potential formulation, we show that the sensitivity can be decomposed into (i) Nernstian contributions and (ii) kinetic contributions from multiple reactions. Consequently, an approximately constant log-linear ln [O2]–Eh sensitivity does not require dominance by a single couple (e.g., O2 H2O); it can also arise when the effective reaction set contributing to the mixed potential and their relative weights remain approximately invariant, suggesting that this relationship can serve as a compact indicator of redox-network stability. To examine whether such slope stability and breakdown are observable in the field, we apply this interpretation to a 21-month, multi-site time series from a constructed shallow pond in Japan, where dissolved oxygen and electrode redox potential were co-measured at weekly fixed depths and along biweekly vertical profiles. Channel excavation produced a pond-wide electrical conductivity anomaly, and change-point detection was used to define pre- and post-disturbance regimes. During the pre-disturbance regime, the ln [O2]–Eh slope was relatively stable across sites. After disturbance, the inflow-proximal site exhibited a weakened slope and systematically elevated Eh relative to the pre-disturbance baseline; notably, baseline-referenced Eh deviations peaked after the EC anomaly had largely relaxed, and a follow-up survey in February 2025 indicated partial recovery. Co-located Eh and oxygen measurements can thus provide a simple, screening-level indicator of departures from a site-specific redox baseline that are consistent with disturbance-driven changes in effective redox conditions and recovery, while recognizing that complementary speciation measurements remain necessary to identify the underlying redox processes and dominant redox couples.
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BibTeX
@article{morimoto2026redoxnetwork,
title = {{Redox-network reconfiguration inferred from the ln[O2]–Eh relationship under mixed-potential conditions in a shallow pond time series}},
author = {Kyoko Morimoto and Mana Ito and Katsutoshi Ito and Mayumi Seto},
journal = {Biogeosciences},
year = {2026},
month = aug,
doi = {10.5194/bg-23-5795-2026},
url = {https://doi.org/10.5194/bg-23-5795-2026},
note = {CC BY},
}
RIS
TY - JOUR
TI - Redox-network reconfiguration inferred from the ln[O2]–Eh relationship under mixed-potential conditions in a shallow pond time series
AU - Kyoko Morimoto
AU - Mana Ito
AU - Katsutoshi Ito
AU - Mayumi Seto
PY - 2026
DA - 2026/08/01
JO - Biogeosciences
DO - 10.5194/bg-23-5795-2026
UR - https://doi.org/10.5194/bg-23-5795-2026
AB - Oxidation–reduction potential (Eh) is widely used as an in situ indicator of redox conditions in aquatic environments, and field electrodes typically record a mixed potential generated by multiple concurrent interfacial redox reactions. Beyond a simple Nernstian interpretation based on a single redox couple, here we ask what mechanistic information can be extracted from an observed relationship between Eh and a single chemical species under mixed-potential conditions, focusing on dissolved oxygen. Using a linearized mixed-potential formulation, we show that the sensitivity can be decomposed into (i) Nernstian contributions and (ii) kinetic contributions from multiple reactions. Consequently, an approximately constant log-linear ln [O2]–Eh sensitivity does not require dominance by a single couple (e.g., O2 H2O); it can also arise when the effective reaction set contributing to the mixed potential and their relative weights remain approximately invariant, suggesting that this relationship can serve as a compact indicator of redox-network stability. To examine whether such slope stability and breakdown are observable in the field, we apply this interpretation to a 21-month, multi-site time series from a constructed shallow pond in Japan, where dissolved oxygen and electrode redox potential were co-measured at weekly fixed depths and along biweekly vertical profiles. Channel excavation produced a pond-wide electrical conductivity anomaly, and change-point detection was used to define pre- and post-disturbance regimes. During the pre-disturbance regime, the ln [O2]–Eh slope was relatively stable across sites. After disturbance, the inflow-proximal site exhibited a weakened slope and systematically elevated Eh relative to the pre-disturbance baseline; notably, baseline-referenced Eh deviations peaked after the EC anomaly had largely relaxed, and a follow-up survey in February 2025 indicated partial recovery. Co-located Eh and oxygen measurements can thus provide a simple, screening-level indicator of departures from a site-specific redox baseline that are consistent with disturbance-driven changes in effective redox conditions and recovery, while recognizing that complementary speciation measurements remain necessary to identify the underlying redox processes and dominant redox couples.
SN - 1726-4170
SN - 1726-4189
ER -