Wetlands store a large proportion of the global terrestrial carbon stock as they are generally net sinks for carbon dioxide (CO2), but are also a significant source of methane (CH4) to the atmosphere due to waterlogged, anoxic conditions. Compared to bogs and fens, swamps are historically understudied, in part due to the lack of consistent definitions across areas, variety of vegetation communities, and misclassification as uplands, bogs, or fens. Swamps are the dominant wetland type in Southern Ontario: understanding carbon dynamics such as net productivity and CH4 production, is crucial especially under a changing climate. Further, swamps may be mineral with organic soil layers, or peatlands with organic layers >40 cm, creating variability in the potential carbon stocks contained within the ecosystem. We undertook a 12-month synoptic study of 12 swamps across Southern Ontario measuring plant-soil-water-atmosphere gas exchange, environmental conditions, soil chemistry, litter inputs, and biomass. There were no significant differences in June through February CH4 or CO2 fluxes among sites, with the exception of a single bog-margin swamp. Vegetation composition and litter inputs, and thus carbon:nitrogen ratios, differed between the swamps, and we explore whether dominant tree type or hydrologic setting can explain these differences. Our findings provide important baseline data and process-based understanding to support the inclusion of swamp ecosystems in local to national models of ecosystem carbon exchange and to evaluate their role as natural climate solutions.