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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 4
Biogeosciences, 9, 1451–1463, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Nitrogen and global change

Biogeosciences, 9, 1451–1463, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 19 Apr 2012

Research article | 19 Apr 2012

Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda

N. Gharahi Ghehi1, C. Werner5, L. Cizungu Ntaboba1, J. J. Mbonigaba Muhinda2, E. Van Ranst3, K. Butterbach-Bahl4, R. Kiese4, and P. Boeckx1 N. Gharahi Ghehi et al.
  • 1Faculty of Bioscience Engineering, Isotope Bioscience Laboratory - ISOFYS, Ghent University, Belgium
  • 2National University of Rwanda (NUR), Department of Soil and Environmental Management (SEM), Rwanda
  • 3Department of Geology and Soil Science, Laboratory of Soil Science, Ghent University, Belgium
  • 4Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany
  • 5Biodiversity and Climate Research Centre (BIK-F), Frankfurt, Germany

Abstract. Globally, tropical forest soils represent the second largest source of N2O and NO. However, there is still considerable uncertainty on the spatial variability and soil properties controlling N trace gas emission. Therefore, we carried out an incubation experiment with soils from 31 locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soils were incubated at three different moisture levels (50, 70 and 90 % water filled pore space (WFPS)) at 17 °C. Nitrous oxide emission varied between 4.5 and 400 μg N m−2 h−1, while NO emission varied from 6.6 to 265 μg N m−2 h−1. Mean N2O emission at different moisture levels was 46.5 ± 11.1 (50 %WFPS), 71.7 ± 11.5 (70 %WFPS) and 98.8 ± 16.4 (90 %WFPS) μg N m−2 h−1, while mean NO emission was 69.3 ± 9.3 (50 %WFPS), 47.1 ± 5.8 (70 %WFPS) and 36.1 ± 4.2 (90 %WFPS) μg N m−2 h−1. The latter suggests that climate (i.e. dry vs. wet season) controls N2O and NO emissions. Positive correlations with soil carbon and nitrogen indicate a biological control over N2O and NO production. But interestingly N2O and NO emissions also showed a positive correlation with free iron and a negative correlation with soil pH (only N2O). The latter suggest that chemo-denitrification might, at least for N2O, be an important production pathway. In conclusion improved understanding and process based modeling of N trace gas emission from tropical forests will benefit from spatially explicit trace gas emission estimates linked to basic soil property data and differentiating between biological and chemical pathways for N trace gas formation.

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