Isotopic Ratios of Tropical Methane Emissions by Atmospheric Measurement

Tropical methane sources are an important part of the global methane budget and include natural wetlands, rice agriculture, biomass burning, ruminants, fossil fuels, and waste. delta C-13(CH4) can provide strong constraints on methane source apportionment. For example, tropical wetlands in this study give delta C-13(CH4) values between -61.5 +/- 2.9% and -53.0 +/- 0.4% and in general are more enriched in C-13 than temperate and boreal wetlands. However, thus far, relatively few measurements of delta C-13(CH4) in methane-enriched air have been made in the tropics. In this study samples have been collected from tropical wetland, rice, ruminant, and biomass burning emissions to the atmosphere. Regional isotopic signatures vary greatly as different processes and source material affect methane signatures. Measurements were made to determine bulk source inputs to the atmosphere, rather than to study individual processes. These measurements provide inputs for regional methane budget models, to constrain emissions with better source apportionment. Plain Language Summary Tropical methane sources are an important part of the global methane budget and include natural wetlands, rice agriculture, biomass burning, ruminants, fossil fuels, and waste. Carbon isotopes in methane can provide strong constraints on methane source apportionment. However, thus far, relatively few measurements of carbon isotopes in methane-enriched air have been made in the tropics. In this study samples have been collected from tropical wetland, rice, ruminant, and biomass burning emissions to atmosphere. Regional isotopic signatures vary greatly as different processes and source material affect methane signatures. Measurements were made to determine bulk source inputs to the atmosphere, rather than to study individual processes, to provide inputs for regional methane budget models, and to constrain emissions with better source apportionment.