Termite mound emissions of CH4 and CO2 are primarily determined by seasonal changes in termite biomass and behaviour

Termites are a highly uncertain component in the global source budgets of CH4 and CO2. Large seasonal variations in termite mound fluxes of CH4 and CO2 have been reported in tropical savannas but the reason for this is largely unknown. This paper investigated the processes that govern these seasonal variations in CH4 and CO2 fluxes from the mounds of Microcerotermes nervosus Hill (Termitidae), a common termite species in Australian tropical savannas. Fluxes of CH4 and CO2 of termite mounds were 3.5-fold greater in the wet season as compared to the dry season and were a direct function of termite biomass. Termite biomass in mound samples was tenfold greater in the wet season compared to the dry season. When expressed per unit termite biomass, termite fluxes were only 1.2 (CH4) and 1.4 (CO2)-fold greater in the wet season as compared to the dry season and could not explain the large seasonal variations in mound fluxes of CH4 and CO2. Seasonal variation in both gas diffusivity through mound walls and CH4 oxidation by mound material was negligible. These results highlight for the first time that seasonal termite population dynamics are the main driver for the observed seasonal differences in mound fluxes of CH4 and CO2. These findings highlight the need to combine measurements of gas fluxes from termite mounds with detailed studies of termite population dynamics to reduce the uncertainty in quantifying seasonal variations in termite mound fluxes of CH4 and CO2.