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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-11
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-11
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 22 Jan 2019

Research article | 22 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Rhizosphere to the atmosphere: contrasting methane pathways, fluxes and geochemical drivers across the terrestrial-aquatic wetland boundary

Luke C. Jeffrey1,2, Damien T. Maher1,2,3, Scott Johnston1, Kylie Maguire1, Andrew D. L. Steven4, and Douglas R. Tait1,2 Luke C. Jeffrey et al.
  • 1SCU Geoscience, Southern Cross University, P.O. Box 157, Lismore, NSW 2480, Australia
  • 2National Marine Science Centre, Southern Cross University, P.O. Box 4321, Coffs Harbour, NSW 2450, Australia
  • 3School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia
  • 4CSIRO Oceans and Atmosphere, Queensland Biosciences Precinct, University of Queensland, 306 Carmody Rd, St Lucia, Brisbane 4067, Australia

Abstract. Although wetlands represent the largest natural source of atmospheric CH4, large uncertainties remain regarding the global CH4 flux. Wetland hydrological oscillations contribute to this uncertainty, dramatically altering wetland area, water table height, soil redox potentials and CH4 emissions. This study compares both terrestrial and aquatic CH4 fluxes over two distinct seasons in both permanent and seasonal remediated freshwater wetlands in subtropical Australia. We account for aquatic CH4 diffusion and ebullition rates, and plant-mediated CH4 fluxes from three distinct vegetation communities, thereby examining seasonal, diurnal and intra-habitat variability. CH4 emission rates were related to underlying sediment geochemistry. For example, distinct negative relationships between Fe(III) and SO42− and CH4 fluxes were observed, whereas distinct positive trends occurred between CH4 emissions and Fe(II) / AVS, where sediment Fe(III) and SO42− were depleted. The highest CH4 emissions of the seasonal wetland were measured during flooded conditions and always during daylight hours, which is consistent with soil redox potential and temperature being important co-drivers of CH4 flux. The highest CH4 fluxes were consistently emitted from the permanent wetland (1.5 to 10.5 mmol m−2 d−1), followed by the Phragmites australis community within the seasonal wetland (0.8 to 2.3 mmol m−2 d−1), whilst the lowest CH4 fluxes came from a region of forested Juncus sp. (−0.01 to 0.1 mmol m−2 d−1) which also corresponded with the highest sedimentary Fe(III) and SO42−. We suggest that wetland remediation strategies should consider geochemical profiles to help to mitigate excessive and unwanted methane emissions, especially during early system recovery periods.

Luke C. Jeffrey et al.
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Luke C. Jeffrey et al.
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Short summary
Wetlands represent the largest natural source of methane (CH4), so understanding CH4 drivers are important for climate models and management. We compared several CH4 pathways of a remediated subtropical Australian wetland. We found permanently innundated sites emitted more CH4 than seasonally innundated sites and that the soil properties within each site strongly correlated to CH4 emissions. This suggests that selective remediation of suitable soil types may help mitigate unwanted CH4 emissions.
Wetlands represent the largest natural source of methane (CH4), so understanding CH4 drivers are...
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