Abstract
Research Highlights: Monitoring of soil CH4 fluxes in African tropical forest conducted run for almost two years, contributing to the scant information on greenhouse gas (GHG) fluxes from forests available from this region. Data showed that the forest soil acted as a net yearly source of CH4. Hotspots of CH4 emissions were measured both in upland and lowland areas of the forest, and on an annual basis they overcame the soil CH4 sink during drier periods or in well-drained areas. Background and Objectives: Atmospheric studies indicate that tropics are a strong CH4 source. Regional budgets attribute the majority of this source to wetland ecosystems and flooded lowland forests, whereas un-flooded forests are considered net CH4 sinks, although few studies in tropical forests, in particular in Africa, are available. The present work aims to contribute to this knowledge gap. Materials and Methods: Monitoring campaigns were conducted along the year in the tropical forest of the Ankasa National Park, Ghana, in two contrasting environments, uphill and downhill, using close static chambers coupled with gas chromatography. Results: The uphill area was a net weak CH4 sink with mean daily fluxes ranging from −1.29 to 0.44 mg CH4 m−2 d−1. The downhill area was a significant CH4 source with mean daily fluxes ranging from −0.67 to 188.09 mg CH4 m−2 d−1 and with peaks up to 1312 mg CH4 m−2 d−1 in the wet season. Conclusions: The net annual soil CH4 budget for the Ankasa Park, normalizing the proportion of downhill areas over the whole park surface, was a source of about 3.3 kg CH4 ha−1 yr−1. Overlooking such areas might lead to underestimates of the total CH4 source strength of forested areas.
Highlights
Methane (CH4 ) is the second most relevant biogenic greenhouse gas, after carbon dioxide, in terms of radiative forcing on the climate [1,2]
For eight of the 98 days of monitoring was the average CH4 flux above zero, and these days mainly occurred in the wet season 2010 (Figure 2)
The average net CH4 source was due to a few chambers characterized by high CH4 emissions among chambers showing almost zero flux, as can be noted by the very high standard error for these days of positive fluxes (Figure 1)
Summary
Methane (CH4 ) is the second most relevant biogenic greenhouse gas, after carbon dioxide, in terms of radiative forcing on the climate [1,2]. As top-down estimates cannot disentangle sources and sinks of CH4 when more processes occur simultaneously, global CH4 estimates have been quantified in combination with bottom-up approaches, mainly process-based modelling and/or inventory [2,3,4]. This detailed analysis indicated that wetlands and forested, flooded or saturated. Forests 2020, 11, 1157 lowlands (permanent and ephemeral) were the most prominent CH4 source in the tropics This source, is characterized by significant uncertainty [3]. The extent of flooded land is computed from remote sensing data or by using hydrological models [3,4,5]
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