The relationships between termite mound CH₄/CO₂ emissions and internal concentration ratios are species specific

Abstract. We investigated the relative importance of CH₄ and CO₂ fluxes from soil and termite mounds at four different sites in the tropical savannas of northern Australia near Darwin and assessed different methods to indirectly predict CH₄ fluxes based on CO₂ fluxes and internal gas concentrations. The annual flux from termite mounds and surrounding soil was dominated by CO₂ with large variations among sites. On a carbon dioxide equivalent (CO₂-e) basis, annual CH₄ flux estimates from termite mounds were 5- to 46-fold smaller than the concurrent annual CO₂ flux estimates. Differences between annual soil CO₂ and soil CH₄ (CO₂-e) fluxes were even greater, soil CO₂ fluxes being almost three orders of magnitude greater than soil CH₄ (CO₂-e) fluxes at site. The contribution of CH₄ and CO₂ emissions from termite mounds to the total CH₄ and CO₂ emissions from termite mounds and soil in CO₂-e was less than 1%. There were significant relationships between mound CH₄ flux and mound CO₂ flux, enabling the prediction of CH₄ flux from measured CO₂ flux; however, these relationships were clearly termite species specific. We also observed significant relationships between mound flux and gas concentration inside mound, for both CH₄ and CO₂, and for all termite species, thereby enabling the prediction of flux from measured mound internal gas concentration. However, these relationships were also termite species specific. Using the relationship between mound internal gas concentration and flux from one species to predict mound fluxes from other termite species (as has been done in the past) would result in errors of more than 5-fold for mound CH₄ flux and 3-fold for mound CO₂ flux. This study highlights that CO₂ fluxes from termite mounds are generally more than one order of magnitude greater than CH₄ fluxes. There are species-specific relationships between CH₄ and CO₂ fluxes from a mound, and between the inside mound concentration of a gas and the mound flux emission of the same gas, but these relationships vary greatly among termite species. Thus, there is no generic relationship that will allow for the accurate prediction of CH₄ fluxes from termite mounds of all species, but given the data limitations, the above methods may still be used with caution.