The contribution of trees to tropical wetland methane emissions

Lead Research Organisation: University of Nottingham
Department Name: Sch of Biosciences

Abstract

Methane (CH4) is an important greenhouse gas that is ~25 times more powerful than CO2 at trapping the Sun's energy. There is therefore considerable interest in the processes involved in CH4 production, principally in waterlogged soils in wetlands, and the processes that lead to its emission to the atmosphere. This study is concerned with processes that enhance the amount of CH4 emitted to the atmosphere, in particular, a novel mechanism for transferring CH4 from soil to the atmosphere.
It is generally thought that CH4 produced in waterlogged soils is emitted by a combination of three processes: 1) by diffusion through water-filled pores, 2) by abrupt release of bubbles, and 3) through internal spaces in the stems of grass-like plants which are adapted to live in waterlogged soils. We propose that the stems of wetland trees also provide an important conduit for the transfer of CH4 from wet soils to the atmosphere, a possibility that to date has been almost entirely overlooked. This project builds on published data gathered by this team which showed that mature temperate wetland alder trees indeed emit CH4 via their trunks, a finding that is corroborated by one other recent study of ash trees in Japan. This is an important finding because wetlands are the largest single source of CH4 emissions to the atmosphere and 60% of these ecosystems are forested. We now have additional unpublished data that was collected in the spring of 2011 (10 weeks before the call deadline) which show that tropical peat swamp forest trees in Borneo emit 65% off all ecosystem methane emissions and twice as much as emissions currently quantified from the peatland surface. At present, researchers working in forested wetlands typically measure only CH4 emitted from the soil surface and thus we assert that the total amount of CH4 being released from these ecosystems is being grossly underestimated.
This oversight in the past may also explain why different ways of estimating CH4 emissions for a region rarely agree. Estimates of CH4 emission obtained from satellite or atmospheric measurements are often greater than estimates based on observations made at ground level. This is particularly evident in forested tropical areas. Our finding that trees enhance venting of CH4 from soil is a possible explanation to account for the discrepancy, in part, because soils in many of the forested areas are flooded either seasonally and in many cases permanently, which means an abundance of CH4 should be present in soils.
We suggest that there are two ways by which CH4 produced in wet soils may be transported and emitted through trees: i) as a gas through air-filled tissue in trees that has formed as an adaptation to enable transfer of oxygen from the atmosphere to the tree's roots which are growing in oxygen-poor waterlogged soil, and ii) dissolved in sap and then liberated to the atmosphere when tree water is lost by transpiration through pores in tree stems and leaves.
In the proposed study we will measure CH4 emissions from tropical wetlands, principally in Borneo but also in Panama using techniques to help distinguish the tree emission routes and establish their contribution to ecosystem methane flux as measured using larger scale micro-meteorological methods. We will also measure the ratio of two naturally occurring 'versions' (isotopes) of carbon: the relatively rare heavy isotope carbon-13 and the lighter more common carbon-12. The ratio of these isotopes of carbon in CH4 in the soil and in tree emissions provides valuable information about how CH4 is produced and how it moves through the tree. Ours will be the first multi-year study of tropical wetland tree emissions which should, for the first time, establish the true contribution of these ecosystems to the atmospheric methane concentration.

Planned Impact

We believe that the subject and research outcomes of this proposal have significant potential for impact with respect to public engagement not only to convey the scientific results, but also to provide the public with insights into the process by which the science is produced thus opening up, to a large audience, the way climate-relevant science is conducted. Additional end-user beneficiaries include government departments and agencies. In Brunei these include the Ministry of Industry and Primary Resources and the Ministry of Forestry, both of whom have a responsibility for forest protection and conservation of carbon stocks. This is further amplified by Brunei's key role in establishing the trans-boundary Heart of Borneo conservation initiative, which encompasses large areas of peat swamp forest. Contacts with the Bruneian government will be facilitated via close links that the team has established with the British Foreign and Commonwealth Office (FCO) in Brunei. There is also considerable interest and support from the regional FCO, which encompasses Malaysia and Indonesia, both of which countries have extensive peatland resources. In addition, there is interest in GHG emissions among agencies and non-governmental organizations (NGOs) where land and ecosystem management is a primary interest. We therefore seek to engage these organisations, including Wetlands International, the WWF and representatives of peatland development agencies (e.g. RSPO) and others with the project so that we may respond to end-user need. Additional end-user beneficiaries will include the IPCC who are soliciting nominations for contributors to the forthcoming IPCC supplement to the 2006 Guidelines for Wetland Contributions to National GHG Inventories.

Much of our public engagement strategy will build on the Open University's existing partnership with the BBC to disseminate with the broadest reach both nationally and internationally. Our public engagement strategy centres around the integrated production and co-production of audio-visual and web materials suitable for i) dissemination of audio-visual content via open access websites (e.g., iTunesU, YouTube, etc.); ii) primetime national (and international) broadcast via the OU's close partnership with the BBC; iii) engagement through new media (e.g., Blogging and micro-blogging; i.e., Twitter and blogging on BBC/OU open2.net)

There is considerable opportunity to inform policy through existing and developing relationships with DECC and NGOs as part of the ongoing MethaneNet activity. We believe it will be essential to convene a project steering committee of end-users at the inception of the project. We will seek to include at least one member of an international body such as the United Nations Environment Programme or a member of the secretariat of the Ramsar Convention on Wetlands and the UK's nominated contributor to the IPCC supplement to the 2006 wetland GHG inventory guidelines.

Institutional Statement:
Additionally, any peer-reviewed publications arising from this grant will be registered on the Open University's open access institutional repository - Open Research Online (ORO) at http://oro.open.ac.uk. ORO is now one of the largest HEI repositories in the UK with over 850,000 visits from people in 170 countries since 2006. It enables access to research outputs via common search engines including Google, by using the OAI (Open Archives Initiative) Protocol for Metadata Harvesting.

Publications

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Sjögersten S (2020) Methane emissions from tree stems in neotropical peatlands. in The New phytologist

 
Description Tropical peatland trees are large emitters of methane while trees going on well drained soils do not emit methane.
Exploitation Route We have developed a fast reliable method for measuring methane emissions from trees and opened up a new research field.
Sectors Environment

 
Description Hydrological investigation of forested tropical peatlands in Panama 
Organisation University of Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution Understanding of site hydrology which is important to understand greenhouse gas emissions
Collaborator Contribution They are carrying out the hydrological assessment of the sites
Impact Field work is ongoing in Panama
Start Year 2014