Methane and Nitrous Oxide Porewater Concentrations and Surface Fluxes of a Regulated River

Researchers conducted multiscale observations for understanding the roles of hyporheic transport and hydrology in river greenhouse gas fluxes.

Image described in caption. The insets show a cross section of the subsurface below a stream (i.e., the hyporheic zone) under different hydrologic conditions, where green water and blue water represent groundwater and surface water, respectively.

A conceptual overview of cross-scale connections among history, ecology, and hydro-biogeochemistry.

[Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0) from Stegen, J. "At the Nexus of History, Ecology, and Hydrobiogeochemistry: Improved Predictions Across Scales Through Integration." mSystems 3(2), (2018). DOI:10.1128/mSystems.00167-17. Insets reprinted under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0) from Stegen, J., et al. "Groundwater–Surface Water Mixing Shifts Ecological Assembly Processes and Stimulates Organic Carbon Turnover." Nature Communications 7, 11237 (2016). DOI:10.1038/ncomms11237.]

The Science

Greenhouse gas (GHG) emissions from rivers are a critical missing component of current global GHG models. Their exclusion is mainly due to a lack of measurements in the field and a poor understanding of the dynamics of GHG production and emissions across space and time, which prevents optimal model parametrization. The researchers combined observations of porewater concentrations along different beach positions and depths and surface fluxes of methane and nitrous in a large regulated river during three water stages: rising, falling, and low.

The Impact

Observations that resolve the processes that link river hydrology and hyporheic transport to production, oxidation, and flux of greenhouse gasses in river sediments can provide key information needed for improving greenhouse gas models.

Summary

Researchers conducted this study to gain insights into the interactions between hydrological exchanges and GHG emissions and elucidate possible hypotheses that could guide future research on the mechanisms of GHG production, consumption, and transport in the hyporheic zone. Observations of dissolved gas in the porewater throughout the soil column and surface flux allow scientists to determine of the effect of hyporheic transport on methane and N2O production in the sediments, and estimate the effects of spatial and temporal variation of conductivity of the soil and water column to methane and N2O transport. This research is the first to report these critical temporal, spatial, and vertical variation patterns of these model parameters. Hyporheic mixing and river stage are important factors in the rate of methane flux from the Columbia River. Researchers found that the river acts as an overall source of methane to the atmosphere. Peak rates were observed at an intermediate depth under low water conditions. The sign of N2O flux changed with river stage. The relationship between soil profile of dissolved gasses and the flux of these gasses varied between methane and N2O and among different times with different river stages.

Principal Investigator

Gil Bohrer
The Ohio State University
[email protected]

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This study was supported by the U.S. Department of Energy, Office of Biological and Environmental Research, as part of the Subsurface Biogeochemical Research project DE-SC0018170 – Accounting for hydrological and microbial processes on greenhouse gas budgets from river systems.

References

Villa, J. A., et al. "Chamber Flux and Porewater Concentration of CH4, CO2 and N2O, 2018, Columbia River Bank at the Hanford Site, WA, USA." ESS-DIVE (2020). https://doi.org/10.15485/1595105.