Methane flux, vertical gradient and mixing ratio measurements in a tropical forest 1Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands
05 Aug 2011
2Universidade Federal do Amazonas (UFAM), Instituto de Educação, Agricultura e Ambiente (IEAA), Campus Vale do Rio Madeira, Rua 29 de Agosto, Centro, Humaitá – AM, Cep – 69800-000, Brazil
3Instituto Nacional de Pesquisas da Amazônia (INPA), Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), Avenida André Araújo, 2936 – Aleixo, Manaus, CEP 69060-000, Brazil
4Instituto de Pesquisa Energéticas e Nucleares (IPEN), Lab. Química Atmosférica (CQMA), Av. Prof. Lineu Prestes, 2242, Cidade Universitaria, Sao Paulo – SP, CEP 05508-900, Brazil
5Embrapa Amazônia Oriental, Tv. Dr. Enéas Pinheiro, s/n, Marco, Caixa postal 48, Belém, PA, CEP 66095-100, Brazil
Received: 21 January 2011 – Published in Atmos. Chem. Phys. Discuss.: 11 February 2011 Abstract. Measurements of CH4 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 CH4 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 CH4 gradient in the
canopy. In the morning hours, a strong canopy venting peak is observed for
both CH4 and CO2, but for CO2 this peak is then superimposed
by photosynthetic uptake, whereas the peak lasts longer for CH4.
Monthly averaged diurnal cycles of the CH4 mixing ratio show a decrease
during daytime and increase during nighttime. The magnitude of the
difference in CH4 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 CH4 increase in the nighttime
boundary layer originates from local sources.
Revised: 14 July 2011 – Accepted: 27 July 2011 – Published: 05 August 2011
Citation: Querino, C. A. S., Smeets, C. J. P. P., Vigano, I., Holzinger, R., Moura, V., Gatti, L. V., Martinewski, A., Manzi, A. O., de Araújo, A. C., and Röckmann, T.: Methane flux, vertical gradient and mixing ratio measurements in a tropical forest, Atmos. Chem. Phys., 11, 7943-7953, doi:10.5194/acp-11-7943-2011, 2011.