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Chronic eutrophication and expanding seasonal hypoxia (O 2 < 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 (NH 4 + , NO 2 − , NO 3 − , N 2 ) across the sediment−water 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 polychaete enhancements of O 2 and nitrogen fluxes were strongly correlated with total animal biomass. Fluxes of O 2 , NH 4 + and N 2 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 O 2 , NH 4 + and N 2 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.

The Lagrangian Transport and Transformation Experiment (LaTTE) study of the Hudson River Plume has now completed 2 of its 3 field seasons. The interdisciplinary study is being conducted in a sustained coastal research observatory that provides a spatial and temporal context for adaptive shipboard sampling. Observations from the second LaTTE field season are used here to describe the processes responsible for a previously unexplained recurrent hypoxia region along the New Jersey coast.

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