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)

Impacts of climate and land use on N2O and CH4 fluxes from tropical ecosystems in the Mt. Kilimanjaro region, Tanzania

“…With both increasing soil moisture and N tot concentrations, N 2 O emissions were higher in the Podocarpus (0.68 kg N ha À1 year À1 ) and particularly in the Ocotea forests (1.13 kg N ha À1 year À1 ). However, these rates are still at the lower end of the annual fluxes reported from other African studies at lower elevations and thus higher MAT (2.3-2.9 kg N ha À1 year À1 Castaldi, Bertolini, Valente, Chiti, & Valentini, 2013;Serca et al, 1994;Werner et al, 2007) and studies of other tropical upland forests worldwide (1-10.1 kg N ha À1 year À1 , from Aini, Hergoualc'h, Smith, & Verchot, 2015;Breuer et al, 2002;Kiese, Hewett, Graham, & Butterbach-Bahl, 2003;Melillo et al, 2001;Meurer et al, 2016;Riley & Vitousek, 1995;Verchot, Hutabarat, Hairiah, & van Noordwijk, 2006;Werner et al, 2007).…”

Remotely sensed canopy nitrogen correlates with nitrous oxide emissions in a lowland tropical rainforest

“…Though tropical forests are broadly considered a strong source of N 2 O to the atmosphere (Vitousek and Matson 1992, Bai et al 2012, Brookshire et al 2017, emission rates also vary widely by up to two orders of magnitude among sites, from 0.1 to > 9 kg N 2 O-N ha À1 yr À1 , with a reported mean of 2.8 kg N 2 O-N ha À1 yr À1 (Erickson et al 2001, Castaldi et al 2013. We measured N 2 O flux rates ranging from 0.13 to 0.41 kg N 2 O-N ha À1 yr À1 in low and high canopy N areas, respectively, and we note that the average canopy N of this landscape sits closer to values categorized as "low", suggesting that high foliar N areas are more akin to hot spots on the landscape.…”

“…We measured N 2 O flux rates ranging from 0.13 to 0.41 kg N 2 O-N ha À1 yr À1 in low and high canopy N areas, respectively, and we note that the average canopy N of this landscape sits closer to values categorized as "low", suggesting that high foliar N areas are more akin to hot spots on the landscape. Though summing monthly measurements is insufficient to generate an accurate annual flux, due to the potential to miss episodic events, there are very few continuous annual measures of N 2 O in any tropical forest (Barton et al, 2015), so that the majority of estimates are generated by methods similar to this one (Castaldi et al 2013). In that context, these rates fall at the low end of the global range, and are consistent with the lower end of the range measured by Weintraub et al (2015) (0.4 kg N 2 O-N ha À1 yr À1 ) at a site adjacent to our study area.…”

Management intensity controls soil N2O fluxes in an Afromontane ecosystem

“…Measurements of GHG fluxes from agricultural and natural ecosystems in Africa are limited (Kimet al, 2016;van Lent et al, 2015). Recently, some studies havemeasured soil N2O emissions from African tropical forests covering lowland (Castaldi et al, 2013;Gharahi Ghehi et al, 2013;Werner et al, 2007b), and montane (Gütlein et al, 2017) forests. However, these studies cover mostly a few weeks and thus do not capture seasonal variability in fluxes (Werner et al, 2007b).…”