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Updated: Jul 22, 2025

Visualizing Methane-Cycling Microbial Dynamics in Coastal Wetlands
Published on: January 31, 2025
Methane cycling in the carbonate critical zone
Andrew Oberhelman1, Jonathan B Martin1, Madison K Flint1
1Department of Geological Sciences, 241 Williamson Hall, PO Box 112120, University of Florida, Gainesville, FL 32611-2120, USA.
Groundwater-surface water exchange in carbonate critical zones influences methane cycling. While methane is produced, natural processes like methanotrophy limit its release, reducing its global carbon cycle impact.
Area of Science:
- Earth Science
- Environmental Science
- Geochemistry
Background:
- Carbonate critical zones (CZ) exhibit significant groundwater-surface water exchange, leading to variable redox conditions.
- Redox state changes influence methane (CH4) production or consumption, impacting its role as a greenhouse gas.
Purpose of the Study:
- To investigate how groundwater-surface water exchange affects redox state and CH4 cycling in the carbonate CZ.
- To measure CH4 concentrations and isotopes in various water sources within the Florida carbonate CZ.
Main Methods:
- Measured CH4 concentrations and 13C isotopes in stream, spring, and well water.
- Assessed groundwater subsurface residence times.
- Calculated CH4 fluxes at spring vents.
Main Results:
- CH4 concentrations ranged from 0.002 to 89 μM, inversely related to residence time in springs.
- Methanotrophy, linked to dissolved oxygen, dominated at short residence times.
- Methanogenesis occurred as groundwater became more reducing after flooding.
- CH4 concentrations were higher in wells than springs, indicating loss during flow.
- CH4 fluxes at springs were mostly negative due to CH4 uptake, limiting atmospheric evasion.
Conclusions:
- Most carbonate CZ springs act as CH4 sinks rather than sources due to methanotrophy.
- Estimated CH4 emissions from Florida springs are significantly lower than those from groundwater abstraction.
- Natural attenuation processes in the carbonate CZ limit the impact of CH4 on the global carbon cycle.
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