Methane flux measurements along a floodplain soil moisture gradient in the Okavango Delta, Botswana

Data-poor tropical wetlands constitute an important source of atmospheric CH(4) in the world. We studied CH(4) fluxes using closed chambers along a soil moisture gradient in a tropical seasonal swamp in the Okavango Delta, Botswana, the sixth largest tropical wetland in the world. The objective of the study was to assess net CH(4) fluxes and controlling environmental factors in the Delta's seasonal floodplains. Net CH(4) emissions from seasonal floodplains in the wetland were estimated at 0.072 ± 0.016 Tg a(−1). Microbial CH(4) oxidation of approximately 2.817 × 10(−3) ± 0.307 × 10(−3) Tg a(−1) in adjacent dry soils of the occasional floodplains accounted for the sink of 4% of the total soil CH(4) emissions from seasonal floodplains. The observed microbial CH(4) sink in the Delta's dry soils is, therefore, comparable to the global average sink of 4–6%. Soil water content (SWC) and soil organic matter were the main environmental factors controlling CH(4) fluxes in both the seasonal and occasional floodplains. The optimum SWC for soil CH(4) emissions and oxidation in the Delta were estimated at 50% and 15%, respectively. Electrical conductivity and pH were poorly correlated (r(2) ≤ 0.11, p < 0.05) with CH(4) fluxes in the seasonal floodplain at Nxaraga. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part1)'.