The role of termite CH<sub>4</sub> emissions on the ecosystem scale: a case study in the Amazon rainforest

Abstract

Abstract. 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 µmol mound−1 s−1 for CO2. A termite emission factor of 0.35 µmol CH4 gtermite-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 ∼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.

Assessing CO2 and CH4 fluxes from mounds of African fungus-growing termites

“…However, considering the high variation associated with the fluxes, it seems obvious that if the sizes of the studied mounds are too close to each other, the relationships between mound volume and gas fluxes are difficult to detect. In this study, the mound volumes ranged from 0.023 to 0.259 m 3 (Table 1) including notably more size variance than the earlier comparable studies (0.02 to 0.077 m 3 ) (Jamali et al, 2013;van Asperen et al, 2021). We found that the measured CO2 fluxes were linearly correlated with the termite mound volume during the wet season (Fig.…”

“…7). Methane fluxes ranged from 0.02 to 3.66 mg CH4-C m -2 h -1 and were 2-20 times lower than those reported in earlier studies (0.4-6 mg CH4-C m -2 h -1 , van Asperen et al, 2021;Jamali et al, 2013). As in earlier chamber measurement studies termites have been other than fungus-growing species, this result was expected: in fungus-growing termites a large proportion of the mound total CO2 fluxes originate from aerobic fungus gardens which seem not to emit measurable amounts of CH4 (Darlington et al, 1997).…”

“…Despite the well-recognized importance of termite mounds as significant sources of greenhouse gases, field studies quantifying gas fluxes from termite mounds are rare and often limited to species that build relatively small mounds. Previous CO2 flux measurements from termite mounds have ranged from 40 to 2246 mg CO2-C m -2 h -1 (van Asperen et al, 2021;Jamali et al, 2013;Brümmer et al, 2009). For wood-feeding termites in Australia, the seasonal variability in CO2 and CH4 was high with larger fluxes occurring during the wet season (Jamali et al, 2013).…”

Chapter 4: Amazonian ecosystems and their ecological functions

“…The accumulation of dead wood from tree mortality can further destabilize the C cycle by increasing forest vulnerability to fire, if these areas are near human-ignition sources.Drought-induced stress from water limitation in terra firme forests can reduce the overall capacity of the forest system to uptake atmospheric CO2 and increase tree mortality in old growth Amazonian forests(Phillips et al 2010, van der Molen et al 2011) (see Section 23.1.3 in Chapter 23). Drought can directly reduce the photosynthetic capacity of forests by promoting stomatal closure) that suggests forest vulnerability to drought is heterogeneous across the Amazon, depending on forest species composition, functional traits, and local environments(Cosme et al 2017, Esquivel- Muelbert et al 2020.…”

Greenhouse gas exchange in the Amazon region : carbon dioxide and methane insights from the Amazon Tall Tower Observatory (ATTO)

“…Upland tree stems and leaf surfaces were suggested as potential sinks (Covey & Megonigal, 2019), yet there are no direct observations of such mechanism. Within the canopy, bromeliads (Martinson et al, 2010) and mounds of soil feeding termites (van Asperen et al, 2021) were found to be large site-specific CH 4 hotspots. The large heterogeneity of the latter sources makes it difficult to upscale them and a potential underestimation of these sources at the ecosystem scale seems likely (SPA, 2021).…”