Methane sources in Amazon tropical forests: analysis of isotopic composition and use of indirect techniques to determine gas balances in these ecosystems

Author(s)

José Mauro Sousa de Moura

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2010-02-19

Examining board members

Reynaldo Luiz Victoria; Adibe Luiz Abdalla; Luciana Vanni Gatti; Jean Pierre Henry Balbaud Ometto; Marcos Sarmet Moreira de Barros Salomão

• Advisor: Reynaldo Luiz Victoria

Abstract

Recent publications called the attention to the role of tropical forests on the budget of some important greenhouse gases. The finding that forests would acting as sink of large amounts of CO2 or as a source of CH4 emitted directly from green and dead leaves under aerobic conditions has motivated scientists worldwide to set experiments in tropical forest areas, especially in the Amazon. This study aims to determine the role of Amazonian upland forests to the regional budget of CH4 through analysis of the stable isotopic composition of methane (\'delta\'13CH4) and the discrimination of its possible sources in the ecosystem. This study also shows the attempt to use of 222Rn soil flux and activity measurements as an indirect tracer for CH4 mixing ratios rates in the vertical profile of upland tropical forests. The measurements of \'delta\'13CH4 were carried out during quarterly campaigns in the period from 2006 to 2008 in the Caxiuana National Forest (C.N.F.) and Tapajos National Forest (T.N.F.). The \'delta\'13CH4 varied from -49.24 to -45.50, with overall means (±SE) equal to -47.63±0.04, and -47.32±0.04 for C.N.F. and T.N.F., respectively. The concentration of CH4 varied from 1.82 to 3.19ppm, with mean (±SE) equal to 2.08±0.02 ppm at C.N.F. and 2.11±0.02ppm at T.N.F.. 222Rn soil flux and activity measurements used in this work were taken in the period of 2000-2002. During this period the 222Rn soil flux varied from 6.86 to 103.30 mBq m-2 s-1, with overall mean equal to 32.49±14.00 mBq m-2 s-1. The values for 222Rn activity along the vertical profile varied from 5.27 to 18.17 Bq m-3, 3.55 to 24.02 Bq m-3, and 3.36 to 18.30 Bq m-3, during the years of 2000, 2001, and 2002, respectively. Estimates of CH4 concentrations and soil fluxes, inferred from 222Rn data, compared favorably with measurements done by gas chromatography, indicating that 222Rn has the potential to provide independent measurements of CH4 fluxes in upland forests (AU)

• FAPESP's process: 05/56386-8 - Isotopic discrimination of sources of methane in tropical forests of Amazonia
• Grantee: José Mauro Sousa de Moura
• Support Opportunities: Scholarships in Brazil - Doctorate