Floodplains occupy a small fraction of Earth’s land surface yet play a disproportionate role in the global carbon cycle. They store large amounts of organic carbon while also serving as hotspots of carbon respiration. Although past work has quantified carbon stocks and residence times, the mechanisms driving floodplain carbon release as CO₂ or CH₄ remain less understood, especially in semi-arid systems that contribute strongly to interannual variability in global models. We investigate carbon dynamics in the middle Rio Grande, New Mexico, USA, where strong hydrologic variability offers a natural laboratory. From May to September 2025, we combined geomorphic analysis with soil CO₂ and CH₄ efflux measurements across three sites representing a range of floodplain conditions. We compared groundwater dynamics, surface conditions, and geomorphology to assess controls on soil respiration. Preliminary results show spatial and temporal variability in CO₂ fluxes. Respiration was highest in vegetated areas, especially in forested floodplain zones and near riverbanks. Fluxes increased from spring into summer, likely reflecting rising temperatures and wetting pulses from monsoon storms. Our findings highlight how geomorphic and hydrologic factors regulate carbon loss, helping refine estimates of carbon cycling and storage potential in arid river corridors.
