Sources and sinks of trace gases in Amazonia and the Cerrado

Abstract

Data for trace gas fluxes (NOx, N2O, and CH4) from the Amazon and cerrado region are presented with focus on the processes of production and consumption of these trace gases in soils and how they may be changed because of land use changes in both regions. Fluxes are controlled by seaonality, soil moisture, soil texture, topography, and fine-root dynamics. Compared to Amazonian forests where the rapid cycling of nitrogen supports large emissions of N2O, nitrification rates and and soil emissions of N oxide gases in the cerrado region are very low. Several studies report CH4 consumption during both wet and dry seasons in forest soils, but there is occasionally net production of CH4 during the wet season. A few studies suggest an unknown source of CH4 from upland forests. As with N oxide emissions, there are few data on CH4 emissions from cerrado soils, but CH4 consumption occurs during both wet and dry seasons. Clearing natural vegetation, burning, fertilization of agricultural lands, intensive cattle ranching, and increasing dominance by legume species in areas under secondary succession after land conversion have all been identified as causes of increasing N2O and NO emissions from tropical regions. Large uncertainties remain for regional estimates of trace gas fluxes. Improvement of models for the N oxides and CH4 fluxes for Amazonia and the cerrado still depends upon gathering more data from sites more widely distributed across two vast biomes and more importantly on basic theory about the controls of emissions from the ecosystem to the atmosphere.

Citation

Bustamante, M.M.C.; Keller, Michael; Silva, D.A. 2009. Sources and sinks of trace gases in Amazonia and the Cerrado. In: Keller, M.; Bustamente, M.; Gash, J.; Dias, P.S., eds. Amazonia and global change. Geophysical Monograph Series. Vol. 186. Washington, DC: American Geophysical Union. p. 337-354.