A fixed methane filter maximizes freshwater emissions under warming

Area of Science:

• Environmental Science
• Microbiology
• Climate Change Research

Background:

• Freshwater ecosystems contribute significantly to global methane (CH4) emissions.
• The microbial 'CH4 filter' regulates CH4 emissions by oxidizing produced CH4 back to CO2 (methanotrophy).
• The long-term impact of natural warming on this CH4 filter efficiency is largely unknown.

Purpose of the Study:

• To investigate how natural warming affects the efficiency of the microbial CH4 filter in freshwater ecosystems over extended periods.
• To understand the microbial community shifts associated with warming and their impact on CH4 cycling.

Main Methods:

• Utilized a natural experiment in high-latitude, geothermally warmed streams across the Northern Hemisphere.
• Analyzed microbial community composition and abundance of methanogens and methanotrophs.
• Quantified CH4 production, oxidation activity, and overall CH4 filter efficiency in response to varying temperatures.

Main Results:

• Warming enhanced CH4 production, correlated with increased methanogen abundance and community shifts.
• CH4 oxidation activity increased with warming, but process-level efficiency did not improve.
• Methanotrophs shifted to less efficient taxa, resulting in a fixed system-level CH4 filter efficiency.
• Consequently, CH4 emissions from warmed streams increased.

Conclusions:

• The microbial CH4 filter efficiency appears to remain constant under natural warming conditions.
• This fixed efficiency, coupled with increased CH4 production, leads to inevitable CH4 emission increases with warming.
• If this response is widespread in global freshwaters, future climate change will likely drive a continuous rise in CH4 emissions.