Fluxes of N2O and CH4 from soils under land use change in Southern Amazonia

Katharina H. E. Meurer1, Hermann F. Jungkunst2, Uwe Franko1, Oliver Spott1, Claus F. Stange3
1 Department Soil Physics, Helmholtz Centre for Environmental Research - UFZ
2 Institute for Environmental Sciences, University Koblenz-Landau
3 Federal Institute for Geosciences and Natural Resources - BGR

P 3.12 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

Globalization came along with in extensive land use changes. Rising demands for soybean across the globe (animal feed for producing cheap meat and dairy products, as well as agro diesel) led to expansions of croplands and cattle pastures also in rather remote areas like Southern Amazonia. Changes in the nitrogen and carbon cycles are not restricted to conversion of forest areas (rainforest and cerrado) but are repeated by the conversion of pasture to cropland and annual management practices. One consequence is altered emissions of the greenhouse gases nitrous oxide (N2O) and methane (CH4) to the atmosphere.

In this context, fluxes of N2O and CH4 from soils from the Brazilian states Mato Grosso (MT) and Pará (PA) will be presented. The focus of the measurements was on the comparison of the dominant land use systems, which were forests, cattle pastures and soybean fields. The study sites are oriented along a climatic gradient following the highway BR-163, which crosses both states in order to ease transportation of goods to global markets via the Amazon River. Data were collected from December 2012 to January 2013 and from October 2013 to February 2014.

The transition from the dry to the wet season and the rainy season were chosen for the measurements as changes from dry to wet soil conditions are known to trigger hot moments of greenhouse gas emissions determining emission values. The closed chamber method was applied to a daily resolution. For each plot (n = 5 per plot) soil temperature and soil water content were determined during each measurement run.

In both periods the rainy season was delayed, enabling the inclusion of comparatively long transition times and thus dry-wet cycles. According to this, N2O fluxes showed strong fluctuations during the transition time and almost zero-fluxes during the rainy season. Fluxes of N2O were very low at the pasture, the cerrado and the soybean field and even negative fluxes have been measured. The forest soil emitted more N2O than the other land use systems, but at the same time acted as a sink for CH4, as well as the cerrado and the soybean field.

The collected data show that there is a strong influence of land use management on N2O and CH4 emission. At the same time the potential of the rainy season to decrease N2O emissions becomes obvious.

Letzte Änderung 04.04.2014