Oxygen and Inorganic Nitrogen Exchange in a Nereis virens (Polychaeta) Bioturbated Sediment-Water System

Abstract

The significance of Nereis virens bioturbation on exchange of oxygen and inorganic nitrogen (ammonium and nitrate) across the sediment-water interface was determined in two laboratory systems: (1) Entire sediment systems, with and without Nereis, and (2) individual worm + burrow systems. Sediment oxygen uptake and ammonium release was augmented 43 and 79%, respectively, by the burrow habit of this polychaete (density 600 m 22). This effect was not due purely to worm metabolism, that only accounted for 11 and 33%, respectively. The residual exchange was promoted by stimulation of microbial metabolism and mineralization in the burrow wall, apparently by mucus secretion serving as a new reactive substrate. The stimulation, however, was reduced by the low oxygen concentration predominating in the sparsely ventilated burrows, reducing aerobic metabolism. Another consequence of the low oxygen conditions was a net nitrate consumption in the burrows by nitrate reduction processes, like denitrification, whereas the oxic surface sediment released a considerable amount of nitrate by net nitrification. The high rate of denitrification was evident from a high O/N ratio in burrow fluxes (23 to 24) compared to surface sediment (16), indicating a loss of nitrogen in the burrow environment.