The role of termite CH4 emissions on the ecosystem scale: a case study in the Amazon rainforest

The magnitude of termite methane (CH4) emissions is still an uncertain part of the global CH4 budget and current emission estimates are based on limited field studies. We present in situ CH4 emission measurements of termite mounds and termite mound subsamples performed in the Amazon rainforest. Emissions from five termite mounds of the species Neocapritermes brasiliensis were measured by use of a large flux chamber connected to a portable gas analyser measuring CH4 and CO2. In addition, the emissions of mound subsamples were measured, after which the termites were counted so that a termite CH4 and CO2 emission factor could be determined. Mound emissions were found to range between 17.0 and 34.8 nmol mound(-1) s(-1) for CH4 and between 1.1 and 13.0 mu mol mound(-1) s(-1) for CO2. A termite emission factor of 0.35 mu mol CH4 g(termite)(-1) h(-1) was found, which is almost twice as high as the only other reported value for the Amazon. By combining mound emission measurements with the termite emission factor, colony sizes could be estimated, which were found to range between 55-125 thousand individuals. Estimates were similar to literature values, and we therefore propose that this method can be used as a quick non-intrusive method to estimate termite colony size in the field. The role of termites in the ecosystem's CH4 budget was evaluated by use of two approaches. Termite mound emission values were combined with local mound density numbers, leading to an estimate of 0.15-0.71 nmol CH4 m(-2) s(-1), on average, emitted by termite mounds. In addition, the termite CH4 emission factor from this study was combined with termite biomass numbers, resulting in an estimate of termite-emitted CH4 of similar to 1.0 nmol m(-2) s(-1). Considering the relatively low net CH4 emissions previously measured at this ecosystem, we expect that termites play an important role in the CH4 budget of this terra firme ecosystem.