Benthic primary production and bacterial denitrification in a Mediterranean eutrophic coastal lagoon

► Benthic fluxes of O2, N2 and inorganic nitrogen were measured in a eutrophic lagoon. ► Sediments with microphytobenthos were net heterotrophic and recycled N. ► Sediments with macroalgae were net autotrophic and acted as temporary N sink. ► Denitrification was not suppressed by macroalgae. ► Macroalgal N uptake was one order of magnitude higher than denitrification.