Are tropical uplands regional hotspots for methane and nitrous oxide?

Lead Research Organisation: University of St Andrews
Department Name: Geography and Sustainable Development

Abstract

Tropical ecosystems are major sources of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O), which are 25 and 298 times more effective than carbon dioxide (CO2), respectively, in trapping long-wave radiation in the atmosphere. Increases in CH4 and N2O concentrations since the start of the Industrial Revolution are responsible for over one-third of global warming, and future changes in the atmospheric budgets of these GHGs have implications for the Earth's climate and environmental conditions. N2O emissions, in particular, are projected to rise in the future due to agricultural expansion and enhanced atmospheric nitrogen deposition. Recent studies of the global budgets of CH4 and N2O using satellite imagery, atmospheric measurements, and modelling suggest that significantly more CH4 and N2O are released from the tropics than previously thought due to unaccounted sources of CH4 and N2O. It is critical for us to identify and characterise these 'missing' sources if we wish to understand the current contribution of the tropics to GHG budgets. Knowledge of these 'missing' sources is also necessary for predicting how tropical GHG emissions are likely to respond to future environmental or climatic change. One strong potential candidate for these 'missing' sources of CH4 and N2O are tropical uplands. Tropical uplands have been conspicuously absent from existing atmospheric budgets, because scientific attention has largely focused on CH4 and N2O emissions from lowland forests, savannas, or wetlands. Studies from tropical uplands suggest that they are potentially large sources of CH4 and N2O, with emissions that are equal to or greater than those from lowland environments. Upland rainforests in Puerto Rico, for example, emit more CH4 than lowland forests, with emission rates that are on par with northern wetlands, the largest natural sources of CH4 worldwide. To address these gaps in knowledge, we will conduct a comprehensive study of CH4 and N2O cycling in the Peruvian Andes, using a mixture of field measurements, controlled environment studies, and mathematical modelling. Specifically, we will: 1. Investigate how CH4 and N2O fluxes vary in space and time along an environmental gradient that spans 3000 m of altitude, from lowland rainforest to upper montane rainforest. 2. Explore how key environmental variables (e.g., plant productivity, climate, soil moisture, carbon and nitrogen availability, oxygen) influence CH4 and N2O emissions. 3. Determine if existing mathematical models are able to simulate CH4 and N2O emissions from tropical ecosystems, adapting these models as necessary to better simulate field observations. 4. Determine if GHG emissions from the Andes are able to account for some of the 'missing' tropical sources of CH4 and N2O by extrapolating our field observations to the regional scale using a combination of mathematical modelling, satellite imagery, and land cover databases (i.e., GIS). The proposed research will greatly advance our understanding of CH4 and N2O emissions for an important but understudied region, and will help us determine the relative contribution of Andean ecosystems to the CH4 and N2O budgets for South America. Knowledge of the emission rates and environmental controls on CH4 and N2O fluxes from upland Andean ecosystems will also help us evaluate whether other tropical uplands are likely to be sources of CH4 and N2O, and assess their potential contributions to the global atmospheric budgets of CH4 and N2O. Lastly, the development and adaptation of mathematical models that accurately simulate tropical CH4 and N2O fluxes will allow us to predict the likely response of tropical uplands to future environmental or climatic change.

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/H006583/1 01/08/2010 31/05/2013 £395,440
NE/H006583/2 Transfer NE/H006583/1 01/10/2013 31/07/2015 £25,708
 
Description We found that upland tropical ecosystems in the Andes are potentially important sources & sinks for methane and nitrous oxide, contributing to the regional atmospheric budgets of these greenhouse gases (GHGs). This challenges existing assumptions that these ecosystems either play a negligible role in regional atmospheric budgets.

For methane, we discovered that tropical montane grasslands are sources of atmospheric methane, whereas montane tropical forests are net atmospheric sinks for methane. Soil redox was the dominant control on methane fluxes from montane grasslands, with higher methane emissions observed from landforms and periods of the year when soils were sub-oxic. In addition, we found that net methane oxidation in montane tropical forest soils was regulated by a combination of nitrogen availability and soil moisture. Inorganic nitrogen availability, in particular the concentration of nitrate, appeared to inhibit net methane uptake. On a regional basis, net atmospheric methane exchange was strongly determined by methane fluxes from montane grasslands, which functioned as regional emission hotspots. Understanding the ecology of these hotspots, their spatial distribution, and activity has wider implications for understanding the regional atmospheric budgets of methane, and the future role of montane ecosystems in regional/global atmospheric chemistry in response to environmental change (e.g. climate change, land-use change).

For nitrous oxide, we found that soil-atmosphere fluxes were highly variable across the elevation gradient, with strongest emission fluxes at lower elevations (pre-montane and lower montane forest) and weakest fluxes at higher elevation (upper montane forest and montane grassland). Nitrous oxide fluxes in pre-montane and lower montane forests were on par with lowland tropical forests (the largest natural sources of nitrous oxide worldwide), which is at odds with previous model extrapolations which predict uniformly low fluxes from montane tropical environments. Nitrous oxide fluxes across the gradient were primarily constrained by nitrogen availability, and secondarily controlled by soil moisture or porosity. Overall, these data suggest that these ecosystems are stronger sources of atmospheric nitrous oxide than previously anticipated.
Exploitation Route The work here can be used my global modellers to better understand the role of the tropics in regulating regional and global exchanges of greenhouse gases. It also provides a clear mechanistic basis for developing better predictive models of ecosystem methane and nitrous oxide cycling in tropical ecosystems.
Sectors Agriculture, Food and Drink,Environment

 
Description FACCE-ERA-NET+ on Climate Smart Agriculture
Amount £1,700,000 (GBP)
Funding ID 618105 
Organisation European Commission 
Department Seventh Framework Programme (FP7)
Sector Public
Country European Union (EU)
Start 12/2014 
End 11/2017
 
Description "Does nitrogen availability limit nitrous oxide flux in the tropical Andes?" at the Andes Biodiversity and Ecosystem Research Group Annual Meeting in Pisac, Peru 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation led to in-depth discussion.

Talk led to planning for future collaborative research efforts.
Year(s) Of Engagement Activity 2013
 
Description "Implications of methane and nitrous oxide exchange for ecosystem global warming potential" at the Malaysian Palm Oil Board in Kuala Lumpur. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact Presentation led to in-depth discussion and planning for collaborative research.

The talk contributed to a successful funding bid from the Malaysia Palm Oil Board.
Year(s) Of Engagement Activity 2013
 
Description "Methane and nitrous oxide fluxes from the tropical Andes" at the James Hutton Institute 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Talk sparked questions an discussions afterwards.

N/A.
Year(s) Of Engagement Activity 2013
 
Description "Sources and sinks of methane and nitrous oxide in the tropical Andes" at the European Geoscience Union meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk led to in-depth discussion afterwards.

Talk led to the publication of a peer-reviewed paper published in a special issue of the journal Biogeosciences.
Year(s) Of Engagement Activity 2012
 
Description Does nitrogen availability limit nitrous oxide flux in the tropical Andes? 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk titled Does Nitrogen availability limit nitrous oxide flux in the tropical Andes at the Andes Biodiversity and Ecosystem Research Group Annual Meeting, Pisac, Peru.
Year(s) Of Engagement Activity 2013
 
Description Greenhouse gas dynamics in the tropical Andes, University of Sheffield 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact Invited talk titled Greenhouse gas dynamics in the tropical Andes at a Research Seminar, University of Sheffield.
Year(s) Of Engagement Activity 2013
 
Description Guest speaker at United World College of Southeast Asia 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Guest speaker. Gave a talk titled "Day in the life of a tropical ecologist".
Year(s) Of Engagement Activity 2015
 
Description Oral presentation at the American Geophysical Union annual meeting in San Francisco. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Oral presentation by former PhD student Viktoria Oliver entitled "Effects of different land-uses on soil organic C pools in Peruvian tropical forests." I was listed as senior author for the presentation. The presentation stimulated lively debate and discussion, and generated interest in the study region.
Year(s) Of Engagement Activity 2013
 
Description Poster presentation at the American Geophysical Union annual meeting in San Francisco 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Poster presentation entitled "Nitrogen limitation of nitrous oxide fluxes in the tropical Andes." The poster presentation stimulated debate and interest from other scientists to conduct research in this study region.
Year(s) Of Engagement Activity 2013
 
Description Research seminar talk at the University of Leicester, UK 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact Gave a talk titled Soil-atmosphere exchange of greenhouse gases in the Peruvian Andes at a Research Seminar, University of Leicester, UK.
Year(s) Of Engagement Activity 2012
 
Description Soil trace gas dynamics in the tropical Andes, University of Oxford. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact Invited talk titled Soil trace gas dynamics in the tropical Andes at a Research Seminar, University of Oxford.
Year(s) Of Engagement Activity 2013