Short-term effects of nereid polychaete size and density on sediment inorganic nitrogen cycling under varying oxygen conditions

Abstract

Chronic eutrophication and expanding seasonal hypoxia (O2 < 63 µM) in estuaries like Chesapeake Bay have altered benthic faunal communities in favor of opportunistic species that can quickly populate organic-rich sediments following hypoxic events. It has been suggested that the biogenic activity of polychaetes can stimulate microbial ammonification, nitrification, and/or denitrification in estuarine sediments as well as increase the fluxes of inorganic nitrogen (NH4 + , NO2 � , NO3 � , N2) across the sedimentwater interface. Results of 2 laboratory experiments with the opportunistic polychaete Alitta (Neanthes) succinea were used to quantify the short-term influence of density and size of surface-feeding polychaetes on denitrification and sediment� water fluxes of inorganic nitrogen under varying oxygen conditions. This study shows that poly- chaete enhancements of O2 and nitrogen fluxes were strongly correlated with total animal bio- mass. Fluxes of O2, NH4 + and N2 were stimulated by presence of animals for both larger and smaller worms, but per capita effects were greater for the deep-burrowing larger polychaetes. With the onset of hypoxic conditions, all density treatments had reductions in O2, NH4 + and N2 fluxes, with the high-density treatment showing the greatest change. Denitrification efficiency was 33% higher for experiments with large worms than for smaller worm treatments, suggesting that the former were more effective in removing fixed nitrogen.