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Abstract Methane (CH4) emissions from wetland ecosystems are controlled by redox conditions in the soil, which are currently underrepresented in Earth system models. Plant-mediated radial oxygen loss (ROL) can increase soil O2availability, affect local redox conditions, and cause heterogeneous distribution of redox-sensitive chemical species at the root scale, which would affect CH4emissions integrated over larger scales. In this study, we used a subsurface geochemical simulator (PFLOTRAN) to quantify the effects of incorporating either spatially homogeneous ROL or more complex heterogeneous ROL on model predictions of porewater solute concentration depth profiles (dissolved organic carbon, methane, sulfate, sulfide) and column integrated CH4fluxes for a tidal coastal wetland. From the heterogeneous ROL simulation, we obtained 18% higher column averaged CH4concentration at the rooting zone but 5% lower total CH4flux compared to simulations of the homogeneous ROL or without ROL. This difference is because lower CH4concentrations occurred in the same rhizosphere volume that was directly connected with plant-mediated transport of CH4from the rooting zone to the atmosphere. Sensitivity analysis indicated that the impacts of heterogeneous ROL on model predictions of porewater oxygen and sulfide concentrations will be more important under conditions of higher ROL fluxes or more heterogeneous root distribution (lower root densities). Despite the small impact on predicted CH4emissions, the simulated ROL drastically reduced porewater concentrations of sulfide, an effective phytotoxin, indicating that incorporating ROL combined with sulfur cycling into ecosystem models could potentially improve predictions of plant productivity in coastal wetland ecosystems.
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Net Methane Production Predicted by Patch Characteristics in a Freshwater Wetland
Abstract Methane (CH4) dynamics in wetlands are spatially variable and difficult to estimate at ecosystem scales. Patches with different plant functional types (PFT) represent discrete units within wetlands that may help characterize patterns in CH4variability. We investigate dissolved porewater CH4concentrations, a representation of net CH4production and potential source of atmospheric flux, in five wetland patches characterized by a dominant PFT or lack of plants. Using soil, porewater, and plant variables we hypothesized to influence CH4, we used three modeling approaches—Classification and regression tree, AIC model selection, and Structural Equation Modeling—to identify direct and indirect influences on porewater CH4dynamics. Across all three models, dissolved porewater CO2concentration was the dominant driver of CH4concentrations, partly through the influence of PFT patches. Plants in each patch type likely had variable influence on CH4via root exudates (a substrate for methanogens), capacity to transport gas (both O2from and CH4to the atmosphere), and plant litter quality which impacted soil respiration and production of CO2in the porewater. We attribute the importance of CO2to the dominant methanogenic pathway we identified, which uses CO2as a terminal electron acceptor. We propose a mechanistic relationship between PFT patches and porewater CH4dynamics which, when combined with sources of CH4loss including methanotrophy, oxidation, or plant‐mediated transport, can provide patch‐scale estimates of CH4flux. Combining these estimates with the distribution of PFTs can improve ecosystem CH4flux estimates in heterogenous wetlands and improve global CH4budgets.
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- Award ID(s):
- 1856200
- PAR ID:
- 10482493
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 129
- Issue:
- 1
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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