Nitrous oxide emissions from soil of an African rain forest in Ghana

Abstract. Recent atmospheric studies have evidenced the imprint of large N₂O sources in tropical/subtropical lands. This source might be attributed to agricultural areas as well as to natural humid ecosystems. The uncertainty related to both sources is very high, due to the scarcity of data and low frequency of sampling in tropical studies, especially for the African continent. The principal objective of this work was to quantify the annual budget of N₂O emissions in an African tropical rain forest. Soil N₂O emissions were measured over 19 months in Ghana, National Park of Ankasa, in uphill and downhill areas, for a total of 119 days of observation. The calculated annual average emission was 2.33 ± 0.20 kg N-N₂O ha⁻¹ yr⁻¹, taking into account the proportion of uphill vs. downhill areas, the latter being characterized by lower N₂O emissions. N₂O fluxes peaked between June and August and were significantly correlated with soil respiration on a daily and monthly basis. No clear correlation was found in the uphill area between N₂O fluxes and soil water content or rain, whereas in the downhill area soil water content concurred with soil respiration in determining N₂O flux variability. The N₂O source strength calculated in this study is very close to those reported for the other two available studies in African rain forests and to the estimated mean derived from worldwide studies in humid tropical forests (2.81 ± 2.02 kg N-N₂O ha⁻¹ yr⁻¹).