ABSTRACT Title of dissertation: POLYCHAETES, HYPOXIA, AND NITROGEN CYCLING IN THE

Benthic macrofauna can play an important role in facilitating some of the microbial mediated processes of nitrogen cycling in estuarine sediments. Declines in benthic macrofauna, like polychaete worms, have been attributed to long-term increases in bottom water hypoxia in Chesapeake Bay. Utilizing a large monitoring dataset including benthic macrofaunal abundance, biomass, and concurrent measures of environmental parameters, I examined how environmental conditions regulate the densities of opportunistic polychaetes in a mesohaline estuarine system. This analysis points to a benthic community dominated by euryhaline, opportunistic polychaete worms (M. viridis, S. benedicti, H. filiformis, A. succinea) which have well adapted but varying responses to hypoxia and other stressful conditions. Results of two 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 sediment-water fluxes of inorganic nitrogen under varying oxygen conditions. Polychaete enhancements of O2 and nitrogen fluxes were strongly correlated with tota