Do methane cycling microbes keep Arctic lakes in check?

How do microbes influence the methane release in the arctics? And how will climate change influence these microorganisms? These questions and more are what a new research project led by Suzanne McGowan of the Netherlands Institute of Ecology (NIOO-KNAW) will try to answer. 

The project, Climate feedbacks and methane cycling in Arctic lakes: enzymes to atmosphere (CLIMET), is awarded funding for 4.5 years of research through the NWO Open Competition Domain Science – XL grant. CLIMET is a collaboration between NIOO, Dutch universities Radboud and Utrecht, Heriot Watt and Northumbria Universities from the UK, the University of Maine and the University of Umeå. McGowan elaborates on the plans for CLIMET and why this subject fills an important gap within climate change research. 

Why is it important to know more about methane in Arctic lakes? 

Why is it important to know more about methane in Arctic lakes? McGowan: “Methane is a 28 times more potent greenhouse gas than carbon dioxide, whose rising concentration in the atmosphere is an important driver of climate change. If warming increases methane emissions from Arctic lakes it could be a consequential climate feedback.” Whether this will happen is still unclear. 

The Arctic is already visibly impacted by climate change. “In the last two years lakes in some areas of Southwest Greenland have turned brown as humic substances and metals such as iron have been mobilised. This abrupt change was associated with a period of extreme rainfall and higher temperatures and it increased methane concentrations in lakes by >70%.”

Methane-producing or -consuming?

To know the effects of warming on the methane emissions a lot more information must be gathered about the microbial composition of Arctic lakes: “Arctic lakes are biological hotspots because they retain liquid water within a predominantly frozen landscape; they host microbes which are active in methane cycling. Microorganisms in lakes play an important role in both the production and the consumption of methane. Some microorganisms produce methane but it is also estimated that up to 90% of methane produced in lakes may be immediately removed by methane-consuming microorganisms, the so-called ‘microbial methane filter’. Understanding which microbes are present in Arctic lakes and what influences the balance between those who produce and those who ‘filter’ methane underlies being able to predict net methane emissions from Arctic lakes.”

Experimenting in Greenland

How will the research consortium study these microorganisms? McGowan explains the diversity of the consortium will help execute the different research techniques necessary to study this subject: “Since we currently don’t have much information on which microorganisms live in Arctic lakes, we will use a combination of genetic and microbiology isolation techniques to identify what is there and to see whether we can find any new organisms. We will also use transcriptomics techniques to work out the activity of the organisms and ask- what are they doing? We will conduct experiments on different types of microbes under different conditions to identify what drives changes in microorganisms and the influences on methane.” NIOO researcher Paul Bodelier is also involved in CLIMET, using his experience with experiments on methane-cycling microorganisms. The research will not only experimentally explore the future, but will also try to learn from the past: “We will use sediment cores to reconstruct changes in microorganisms over past centuries to see whether there is evidence that past climate changes have altered methane producing or consuming microbes.” All this research will focus on the Arctic lakes in the district of Kangerlussuaq in West Greenland.

Arctic lakes will play a large role

McGowan expects the Arctic lakes to play a large role in methane cycling: “The Arctic is warming four times more rapidly than the rest of the Earth, increasing the mobilisation of frozen carbon from soils and melting of glaciers. We think that these changes within the landscape could be consequential for methane production in lakes.” She explains the freed-up carbon and nutrients can end up in lakes and influence the microbiota there. “We think that these changing drivers could be important in determining whether methane-producing or methane-consuming microorganisms become most dominant in lakes and so whether lakes are net methane emitters.” 

Lanthanides a missing link?

The newly available carbon is not the only thing expected to influence the methane-consuming microbes. A recent discovery found that elements from the lanthanide group were present in the “methane filter” microbes. The consortium wants to find out if these elements could be the missing link to when and why these methane-consuming microorganisms are active, “Some of our previous work has shown that lanthanide group elements are abundant in dust which originates from the Greenland Ice Sheet. We know very little about the lanthanide cycle in environmental settings so beyond the specific methane question, we hope to address fundamental questions on biogeochemical cycling of little-studied elements.”