Sediment properties modulate the bioturbation effects of Tubifex spp. on CH4 and CO2 emissions in freshwater ecosystems

Freshwater ecosystems are major natural sources of methane (CH 4 ) and carbon dioxide (CO 2 ), with large amounts of these gases being produced in sediments. Bioturbators such as Tubifex spp. have been proposed to alter the dynamics of both gases as they inhabit the sediment–water interface, influencing biogeochemical processes. Although eutrophication generally leads to strong shifts in the benthic community, Tubifex spp. tolerate eutrophication. However, their role in modulating greenhouse gas (GHG) emissions requires further elucidation. We used 24 microcosm to assess the presence of Tubifex spp. on diffusive and ebullitive CH 4 and CO 2 emissions across three eutrophic sediments: one with clay (C) and two with peat, containing low and high organic matter content (P-lom and P-hom, respectively). The effects of Tubifex on carbon emissions varied across emission pathways and were modulated by sediment types. Tubifex presence tended to alter diffusive CH 4 and CO 2 fluxes, leading to higher mean CO 2 and total mean CH 4 emissions in P-lom sediments, whereas weak effects of bioturbation were observed in P-hom and C sediments. The variation in effects was likely associated with sediment-dependent differences in Tubifex bioturbation intensity, as well as Tubificid-mediated shifts in interactions among organic carbon dynamics, CH 4 -cycling microbial abundances, nutrient availability and gaseous carbon fluxes. We did not find evidence that Tubifex affected ebullitive CH 4 emissions, sediment oxygenation or the abundance of methanogens and methanotrophs in the sediment. We conclude that to incorporate their effects in GHG emission estimates, more context-dependent insights are needed.