For much of my recent work I have been investigating how sulfur pollution in acid rain limits the emission of methane gas from natural wetlands.

(You might like to listen to a radio discussion on this work further down this page. Look for the radio icon).

Methane (CH4) is an important gas for two reasons: 1) it is a powerful greenhouse gas (1 molecule of CH4 is roughly 20 times more powerful at trapping the sun’s rays than 1 molecule of CO2) and 2) it plays an important role in atmospheric chemistry.
Wetlands are the largest individual source of this gas so anything that affects the emission of CH4 could have potentially important consequences for Earth’s radiative balance.

The sulfate component of acid rain stimulates a group of microbes (called sulfate reducing bacteria - SRB) to outcompete methane producing microbes (methanogens) when in direct competition for mutual substrates (food). This results in less methane being emitted from natural wetlands. The figure to the left shows this interaction in simple terms (click to enlarge, from Schimel 2004)

Yes. On a local level we have found that individual peatlands impacted by acid rain can be emitting as much a 40% less methane. On a global scale our findings indicate that acid rain may be keeping a partial 'lid' on the global wetland methane source. This effect may be large enough to offset the predicted growth in wetland CH4 emissions brought about by global warming...at least until the middle part of this century.

We are now investigating these interactions via a new NERC supported project 'Regional Integration of CH4 Emission Studies (RICHES)' which seeks to integrate methane emission data from sites that span existing deposition gradients. This work is being carried out by Zoe Wallage. Please follow the link below to access further details on the project and to find out how you can help (if you have any wetland CH4 emission data!).

The RICHES project page

Click on the radio icon to hear John Humphrys and Tim Hirsch discuss the work on Radio 4's 'Today'. August 3rd 2004

For radio interviews on the work, see the 'News' section.

This work has been funded by a variety of sources including the Natural Environment Research Council, NASA and The Open University.

This work is a collaborative effort with input from a number of people:

Nancy Dise (Manchester Metropolitan University)
David Fowler (CEH Edinburgh)
Elaine Matthews (NASA GISS)
Dorothy Koch (NASA GISS)
Bernadette Walter (NASA GISS)
Gunnar Granberg (Umea, Se)
Melanie Vile (Academy of Natural Sciences, USA)

Schimel J. 2004 Playing scales in the methane cycle: From microbial ecology to the globe
PNAS 101: 12400-12401.

For other references, PDFs and links to press releases please click on my 'Recent Publications' page.