Carbon Dioxide and Methane Fluxes from a Tropical Freshwater Wetland Under Natural and Rice Paddy Conditions: Implications for Climate Change Mitigation

Abstract

We investigated the impact of converting a natural tropical freshwater wetland in Uganda into a rice paddy wetland on climate change mitigation, by comparing carbon dioxide (CO2) and methane (CH4) fluxes from the natural section (under different vegetation communities dominated by Cyperus papyrus, Typha latifolia and Phragmites mauritianus) and from a rice paddy section, during the dry and wet seasons. CO2 fluxes (mg C m− 2 h− 1) from the rice paddy section during the dry and wet seasons were 1045.4 ± 46.6 (mean ± SE) and 804.4 ± 50.2 respectively, significantly higher (p < 0.05) than those obtained from all the three vegetation communities of the natural section. However, CH4 fluxes (mg C m− 2 h− 1) from the rice paddy section during the dry and wet seasons were 2.1 ± 0.4 and 5.1 ± 0.5 respectively, significantly lower (p < 0.05) than those observed from all the vegetation communities of the natural section. Considering total carbon emission, it was observed that whereas conversion of natural tropical freshwater wetlands into rice paddies may limit CH4 emission, it compromises climate change mitigation efforts by increasing total carbon emission, that could make rice paddy wetlands net carbon sources. Fluxes of CO2 and CH4 from the wetland were mainly influenced by water level. Further, we estimated that rice paddy wetlands currently emit only 0.72 and 0.14 % of the total annual CO2 and CH4 respectively, emitted from Uganda’s wetland soils due to their low spatial coverage. However, we predict that future emission of both gases from Uganda’s wetlands will mainly originate from rice paddy wetlands due to their rapid expansion rate.