Tropical forest CH4 budget: the importance of local hotspots

<p>Methane (CH₄) is one of the most important anthropogenic greenhouse gases. Despite its importance, natural sources of methane, such as tropical wetlands and termites, are still not well understood and a large source of uncertainty in the tropical CH₄ budget. The Amazon rainforest is a key region for the (global) CH₄ budget but, due to its remote location, local CH₄ concentration and flux measurements are still rare.</p><p>Fieldsite ZF2 (60 km NW of Manaus, Brazil) is located in pristine tropical rain forest. At this fieldsite, a Spectronus FTIR-analyzer (measuring CO₂, CO, CH₄, N₂O & &#948;¹³CO₂) was installed at the foot of the K34 tower, set up to measure different heights above and below the canopy continuously. In addition, by use of a Los Gatos portable analyzer (measuring CO₂ & CH₄), additional semi-continuous concentration measurements were performed at the valley tower (studying the nighttime build up of valley CH₄), above the igarap&#233;&#160; (capturing the CH₄ ebullition bubbles leaving the water surface), and on the plateau (studying the spatial horizontal heterogeneity of CH₄ concentrations within the canopy). Furthermore, the portable analyzer was used for soil, water, termite mound, and termites flux measurements.</p><p>By combining tower and flux chamber measurements, the role and magnitude of different ecosystem sources could be assessed. We observed that, while soils in the valley are a small source of CH₄ (0.1 to 0.2 nmol CH₄ m^-2 s^-1), overall the soils of this ecosystem are expected to be a net CH₄ sink (-0.3 to -0.5 nmol m^-2 s^-1). Estimated total ecosystem CH₄ flux, based on nighttime concentration analyses of the tower data, indicate that the ecosystem is a net CH₄ source (~1 to 2 nmol CH₄ m^-2 s^-1). We propose that the net CH₄ emission of the ecosystem is driven by local emitting hotspots, such as the valley stream and standing water, termites and termite mounds (~1 nmol CH₄ m^-2 s^-1), anoxic soil spots and decaying dead wood.</p><p>&#160;</p>