Methane flux, vertical gradient and mixing ratio measurements in a tropical forest

Abstract

Abstract. Measurements of CH 4 mixing ratio, vertical gradients and turbulent fluxes were carried out in a tropical forest (Reserva Biológica Cuieiras), about 60 km north of Manaus, Brazil. The methane mixing ratio and flux measurements were performed at a height of 53 m (canopy height 35 m). In addition, vertical CH 4 gradients were measured within the canopy using custom made air samplers at levels of 2, 16 and 36 m above ground. The methane gradients within the canopy reveal that there is a continuous methane source at the surface. No clear evidence for aerobic methane emission from the canopy was found. The methane fluxes above the canopy are small but consistently upwards with a maximum early in the morning. The measured fluxes are in agreement with the observed CH 4 gradient in the canopy. In the morning hours, a strong canopy venting peak is observed for both CH 4 and CO 2 , but for CO 2 this peak is then superimposed by photosynthetic uptake, whereas the peak lasts longer for CH 4 . Monthly averaged diurnal cycles of the CH 4 mixing ratio show a decrease during daytime and increase during nighttime. The magnitude of the difference in CH 4 mixing ratio between day and night gradually increases throughout the wet season. The fluxes required to explain the nighttime increase are in agreement with the nighttime fluxes measured above the canopy, which implies that the CH 4 increase in the nighttime boundary layer originates from local sources.

Observations of reactive nitrogen oxide fluxes by eddy covariance above two midlatitude North American mixed hardwood forests

“…If noise is truly random, there should not be significant covariance with fluctuations in vertical wind; however this has been observed in other situations (e.g. methane fluxes reported in Querino et al (2011) and Smeets et al (2009)). In the case of PROPHET, we see a less marked increase in cospectral power at the high frequencies, indicating that perhaps noise was less of an issue during this campaign.…”

Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment

“…Alternatively, one can determine the H 2 O effects in the sampling line before it is deployed in the field (cf. Querino et al, 2011), or the air sample may be dried; however, none of the driers completely removes H 2 O from the air samples. There is always some residual H 2 O left, although it does not necessarily significantly affect the CH 4 fluxes.…”

Comparison of CH4 inversions based on 15 months of GOSAT and SCIAMACHY observations

“…Further development of the SCIAMACHY IMAP XCH 4 retrieval showed that part of the strong methane signal in the tropics was caused by spectroscopic uncertainties [ Frankenberg et al , , ]. Aerobic CH 4 emissions from living plants were found to be far lower than initially suggested [ Dueck et al , ; Nisbet et al , ; Keppler et al , ; Vigano , ; Querino et al , ] and may be insignificant for the global budget. Recent inversions using SCIAMACHY still show a disagreement between tropical bottom‐up methane emissions inventories and emission estimates derived from satellite observations [ Bergamaschi et al , ], which points to remaining uncertainties in tropical methane emissions, most likely related to underestimated wetland emissions.…”