Floating iron biofilms as hidden barriers to methane emissions in wetlands

Sha Zhang; Qianrui Huangfu; Dong Zhu; Zheng Chen

doi:10.59717/j.xinn-geo.2025.100161

The Innovation Geoscience > 2025 Vol. 3 > No. 4 > 100161

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Floating iron biofilms as hidden barriers to methane emissions in wetlands

1.
State Key Laboratory of Regional and Urban Ecology, Ningbo Observation and Research Station, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
2.
Zhejiang Key Laboratory of Pollution Control for Port-Petrochemical Industry, CAS Haixi Industrial Technology Innovation Center in Beilun, Ningbo 315830, China
3.
Department of Health and Environmental Sciences, Xi’an Jiaotong-Liverpool University, 111 Ren’ai Road, Suzhou 215123, China

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Corresponding author: Zheng.Chen@xjtlu.edu.cn
Received Date: March 23, 2025

Accepted Date: July 16, 2025

Published Online: July 29, 2025

The Innovation Geoscience 3(4), https://doi.org/10.59717/j.xinn-geo.2025.100161 | Cite this article

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PUBLIC SUMMARY
1. Iron biofilms, iridescent or rust-stained, are widely observed in shallow water systems.
  
  Iron biofilms at wetland water-air interfaces can reduce methane emissions by up to 6.9-fold.
  
  We challenge the long-held idea that methane oxidation occurs mainly at the sediment-water interface.
  
  Iron biofilms are long-lasting, sustaining their methane-barrier function over time
  
  This process offers a nature-based solution for controlling methane emissions in wetlands.

ABSTRACT

ABSTRACT

Wetland methane emissions are primarily mitigated by microbial oxidation at the sediment-water interface (SWI). Yet, this paradigm fails to explain persistent methane oversaturation in surface waters and lower-than-expected emissions. Here, we demonstrate an overlooked methane barrier formed at water–air interfaces (WAI) by self-organized iron biofilms. Organic matter inputs destabilize the SWI, enabling ferrous iron to diffuse upward and become oxidized, resulting in the formation of iron biofilms ranging in thicknesses from nanometers to centimeters at the WAI. This iron film barrier reduces methane emissions by 2.4- to 6.9-fold through physical entrapment and microbial oxidation (e.g., pmoA gene abundance: 2.1×10⁸ copies m⁻²), involving communities dominated by aerobic and facultative heterotrophs, as well as nitrate- and sulfur-respiring taxa. The dual methane-barrier paradigm explains emission paradoxes in straw-amended environments. This mechanism, absent from the Intergovernmental Panel on Climate Change models, could revise global methane budget estimates and guide nature-based solutions to mitigate wetland methane emissions.
- iron biofilm /
- methane oxidation /
- sediment–water interface /
- air–water interface /
- nature-based solutions /
- carbon neutrality

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Zhang S., Huangfu Q., Zhu D., et al. (2025). Floating iron biofilms as hidden barriers to methane emissions in wetlands. The Innovation Geoscience 3:100161. https://doi.org/10.59717/j.xinn-geo.2025.100161

Zhang S., Huangfu Q., Zhu D., et al. (2025). Floating iron biofilms as hidden barriers to methane emissions in wetlands. The Innovation Geoscience 3:100161. https://doi.org/10.59717/j.xinn-geo.2025.100161

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Floating iron biofilms as hidden barriers to methane emissions in wetlands

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