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

• Main Authors: H. van Asperen, J. R. Alves-Oliveira, T. Warneke, B. Forsberg, A. C. de Araújo, J. Notholt
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-04-01
• Series: Biogeosciences
• Online Access: https://bg.copernicus.org/articles/18/2609/2021/bg-18-2609-2021.pdf
• ISSN: 1726-4170; 1726-4189

<p>The magnitude of termite methane (<span class="inline-formula">CH₄</span>) emissions is still an uncertain part of the global <span class="inline-formula">CH₄</span> budget and current emission estimates are based on limited field studies. We present in situ <span class="inline-formula">CH₄</span> emission measurements of termite mounds and termite mound subsamples performed in the Amazon rainforest. Emissions from five termite mounds of the species <i>Neocapritermes brasiliensis</i> were measured by use of a large flux chamber connected to a portable gas analyser measuring <span class="inline-formula">CH₄</span> and <span class="inline-formula">CO₂</span>. In addition, the emissions of mound subsamples were measured, after which the termites were counted so that a termite <span class="inline-formula">CH₄</span> and <span class="inline-formula">CO₂</span> emission factor could be determined.</p> <p>Mound emissions were found to range between 17.0 and 34.8 nmol mound<span class="inline-formula">⁻¹</span> s<span class="inline-formula">⁻¹</span> for <span class="inline-formula">CH₄</span> and between 1.1 and 13.0 <span class="inline-formula">µ</span>mol mound<span class="inline-formula">⁻¹</span> s<span class="inline-formula">⁻¹</span> for <span class="inline-formula">CO₂</span>. A termite emission factor of 0.35 <span class="inline-formula">µ</span>mol <span class="inline-formula">CH₄</span> g<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mtext>termite</mtext><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="74152ff46135ab59d21c50c6502c0d60"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-2609-2021-ie00001.svg" width="27pt" height="17pt" src="bg-18-2609-2021-ie00001.png"/></svg:svg></span></span> h<span class="inline-formula">⁻¹</span> 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.</p> <p>The role of termites in the ecosystem's <span class="inline-formula">CH₄</span> 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 <span class="inline-formula">CH₄</span> m<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹</span>, on average, emitted by termite mounds. In addition, the termite <span class="inline-formula">CH₄</span> emission factor from this study was combined with termite biomass numbers, resulting in an estimate of termite-emitted <span class="inline-formula">CH₄</span> of <span class="inline-formula">∼1.0</span> nmol m<span class="inline-formula">⁻²</span> s<span class="inline-formula">⁻¹</span>. Considering the relatively low net <span class="inline-formula">CH₄</span> emissions previously measured at this ecosystem, we expect that termites play an important role in the <span class="inline-formula">CH₄</span> budget of this <i>terra firme</i> ecosystem.</p>