Abstract
Carbon emissions to the atmosphere from inland waters are globally significant and mainly occur at tropical latitudes. However, processes controlling the intensity of CO2 and CH4 emissions from tropical inland waters remain poorly understood. Here, we report a data-set of concurrent measurements of the partial pressure of CO2 (pCO2) and dissolved CH4 concentrations in the Amazon (n = 136) and the Congo (n = 280) Rivers. The pCO2 values in the Amazon mainstem were significantly higher than in the Congo, contrasting with CH4 concentrations that were higher in the Congo than in the Amazon. Large-scale patterns in pCO2 across different lowland tropical basins can be apprehended with a relatively simple statistical model related to the extent of wetlands within the basin, showing that, in addition to non-flooded vegetation, wetlands also contribute to CO2 in river channels. On the other hand, dynamics of dissolved CH4 in river channels are less straightforward to predict, and are related to the way hydrology modulates the connectivity between wetlands and river channels.
Highlights
The C emissions from inland waters result from complex interactions between hydrology, biogeochemical processing within the aquatic environment and connectivity with riparian zones and the watershed
The CO2 emissions from inland waters have been traditionally interpreted as mainly resulting from the in-situ degradation of organic C from non-flooded land[7,8,9,10,11,12,13,14,15]
For a given pCO2 value, CH4 concentrations were systematically higher in the Congo than in the Amazon (Fig. 3a–c)
Summary
The C emissions from inland waters result from complex interactions between hydrology, biogeochemical processing within the aquatic environment and connectivity with riparian zones and the watershed. In the Central Amazon basin, CO2 and CH4 emissions from floodplain lakes[23,25] and from river channels[24,26] have been attributed to C from wetlands (flooded forest and macrophytes) in addition to non-flooded terrestrial organic C This was established with a mass balance approach of organic C23,26, high-resolution pCO2 distributions[24], and stable-isotope signatures of organic C. In African rivers, spatial patterns of pCO2 and CH4 relate to the distribution of the fraction of wetland in the catchment within a given system (Congo and Zambezi) and across different basins[27,28] Both non-flooded terrestrial biomass and wetlands contribute to CO2 emissions from inland waters and their relative importance remains uncertain and has not yet been quantitatively resolved[27,29]. The aim of this study is to determine the extent to which the patterns of CO2 and CH4 differ or converge in these two tropical giant water bodies
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