Riparian areas are transition zones between terrestrial and aquatic ecosystems. Seasonal flooding may result in fluctuations between aerobic/anaerobic conditions, stimulating microbial activity leading to carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) production. Because of their high levels of organic matter and soil moisture, riparian areas are ideal habitats for earthworms, which can in turn increase microorganism activity. Our objective was to measure the earthworm-mediated effect on CO₂, N₂Oand CH₄ fluxes in riparian areas, and we hypothesized that earthworms would stimulate microbial activity in riparian soils, leading to a significant increase in CO₂ production under aerobic conditions and greater production of N₂O and CH₄ oxidation from riparian areas along the Riviere-aux-Brochets, Quebec. Three riparian agroecosystems, riparian forest and upland forest sites were selected for the study. Six non-steady-state gas chambers were installed at each site - three chambers measure gas production with ambient earthworm populations while the other three measure gas produced by artificially elevated earthworm populations in 1m² enclosures. The enclosures were constructed by lining them with a 30 cm-deep trench with 2-ply heavy-duty polyethylene film. Enclosures were inoculated with 300 Apporectodea spp. and 60 L. terrestris to increase the ambient population by 30-100% m^-2. All chambers had a permanent base installed to a depth of 10 cm and are capped with a closed-top chamber equipped with a septa and vent. Gases are collected from the headspace 0, 7, 14, and 21 minutes after the chamber is closed and injected into pre-evacuated 20mL exetainers for storage until analysis by gas chromatography. Gas fluxes will be measured repeatedly from April to November 2011. Ancillary measurements including soil moisture and soil temperature will be made to better predict environmental conditions that may modulate the earthworm effect on CO₂, N₂O and CH₄ throughout the frost-free period in temperate riparian areas. Preliminary results will be presented.