Greenhouse gas fluxes in different vegetation types along an African tropical wetland

Abstract

This study quantified how vegetation type and seasonality influence soil–atmosphere exchanges of CO 2 , CH 4 , and N 2 O across Lubigi Wetland, an urban tropical wetland in Uganda receiving wastewater effluent and stormwater from Kampala. Four sites were examined: an upstream Vossia cuspidata zone near inflows, an upstream non-vegetated mudflat, a midstream Phragmites mauritianus stand, and a downstream Cyperus papyrus section. Monthly static chamber measurements were conducted over 12 months, spanning wet and dry seasons, to assess spatial and temporal flux patterns, calculate site-specific global warming potentials (GWPs), and relate emissions to hydrology and soil characteristics. CO 2 and N 2 O fluxes peaked during the dry season, especially in the upstream Vossia zone. CH 4 emissions were also highest in the dry season, with Phragmites areas producing the strongest fluxes and mudflats the lowest. Hydrology was the main controlling factor: water levels below 50 cm promoted CO 2 and N 2 O hotspots, while levels above 50 cm favored CH 4 emissions. Across the wetland, CH 4 contributed the largest share of annual GWP (about 55.6%), followed by CO 2 (39.8%). The highest GWP occurred in the Phragmites zone due to sustained CH 4 emissions, while mudflats had the lowest. Carbon and nitrogen cycles were tightly linked, with negative CO 2 –CH 4 and positive CO 2 –N 2 O relationships. CH 4 emissions were positively associated with microbial biomass carbon and negatively with bulk density. Vegetated soils contained higher organic carbon and nitrogen than mudflats. Management should prioritize CH 4 mitigation, improve wastewater treatment, and apply seasonally adaptive water-level management to reduce overall GWP while maintaining ecosystem functions.