Carbon dioxide and methane emissions from interfluvial wetlands in the upper Negro River basin, Brazil

Abstract

Extensive interfluvial wetlands occur in the upper Negro River basin (Brazil) and contain a mosaic of vegetation dominated by emergent grasses and sedges with patches of shrubs and palms. To characterize the release of carbon dioxide and methane from these habitats, diffusive and ebullitive emissions and transport through plant aerenchyma were measured monthly during 2005 in permanently and seasonally flooded areas. CO2 emissions averaged 2193 mg C m−2 day−1. Methane was consumed in unflooded environments and emitted in flooded environments with average values of −4.8 and 60 mg C m−2 day−1, respectively. Bubbles were emitted primarily during falling water periods when hydrostatic pressure at the sediment–water interface declined. CO2 and CH4 emissions increased when dissolved O2 decreased and vegetation was more abundant. Total area and seasonally varying flooded areas for two wetlands, located north and south of the Negro River, were determined through analysis of synthetic aperture radar and optical remotely sensed data. The combined areas of these two wetlands (3000 km2) emitted 1147 Gg C year−1 as CO2 and 31 Gg C year−1 as CH4. If these rates are extrapolated to the area occupied by hydromorphic soils in the upper Negro basin, 63 Tg C year−1 of CO2 and 1.7 Tg C year−1 as CH4 are estimated as the regional evasion to the atmosphere.