Spatial and temporal dynamics of diffusive methane

Authors: Mangaliso J Gondwe Wellington R L Masamba

Publish Date: 2013/09/18

Volume: 22, Issue: 1, Pages: 63-78

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Abstract

Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases carbon dioxide methane CH4 and nitrous oxide Wetlands constitute the largest single natural source of atmospheric CH4 in the world contributing between 100 and 231 Tg year−1 to the total budget of 503–610 Tg year−1 approximately 60  of which is emitted from tropical wetlands We conducted diffusive CH4 emission measurements using static chambers in river channels floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta Botswana Diffusive CH4 emission rates varied between 024 and 293 mg CH4 m−2 h−1 with a mean ±SE emission of 232 ± 22 mg CH4 m−2 h−1 or 558 ± 53 mg CH4 m−2 day−1 These emission rates lie within the range reported for other tropical wetlands The emission rates were significantly higher P  0007 in permanent than in seasonal swamps River channels exhibited the highest average fluxes at 313 ± 54 mg CH4 m−2 h−1 than in floodplains 204 ± 25 mg CH4 m−2 h−1 and lagoons 169 ± 26 mg CH4 m−2 h−1 Diffusive CH4 emissions in the Delta were probably regulated by temperature since emissions were highest 20–300 mg CH4 m−2 h−1 and lowest 02–30 mg m−2 h−1 during the warmerrainy and cooler winter seasons respectively Surface water temperatures between December 2010 and January 2012 varied from 153 °C in winter to 33 °C in summer Assuming mean inundation of 9000 km2 the Delta’s annual diffusive emission was estimated at 18 ± 02 Tg accounting for 28 ± 03  of the total CH4 emission from global tropical wetlandsThis study was funded by the global change SysTem for Analysis Research and Training START Washington DC through a 2009 GEC Water/Land Research Grant to Dr Kelebogile Mfundisi and the Office of Research and Development of the University of Botswana UBORD research grants to the second author Guma Lagoon Camp provided camping space selfcatering facility and boat to the research team during sampling at Guma on the northwestern side of the Okavango Delta The authors are grateful to Prof Robert E Hecky of the University of MinnesotaDuluth USA for reviewing the first draft of the manuscript We are also grateful to Ms Kenelwe Kgokong and Ms Minsozi Zinzy Mujo who participated in the project as research assistants We do not forget nor underrate the valuable field assistance provided by Messrs Kaelo Makati Wilfred Khaneguba and Ineelo J Mosie

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