Denitrification activity in sediment surrounding polychaete (Ceratonereis aequisetis) burrows

Abstract

The effect of burrow-dwelling fauna on sediment denitrification within the Swan River Estuary, Western Australia, was assessed by determining the spatial profile of potential denitrification activity surrounding individual burrows of a polychaete. This activity was described for Ceratonereis aequisetis and compared with uninhabited sediment. Potential porewater denitrification activity was measured as N’₂O production in the presence of acetylene (which blocks N₂O reduction and NH₄⁺ oxidation) and supplementary NO₃^-(provided as a substrate for denitrification). Snap-freezing of sediment cores in liquid nitrogen allowed easy sectioning in both the vertical (perpendicular depth from surface sediment) and radial (depth from burrow wall) planes. Overall, potential denitrification activity was significantly greater in inhabited sediment than in uninhabited sediment, although uninhabited sediment had higher surficial (0–10 mm) potential denitrification activity. Potential denitrification activity was also greater closer to the burrow wall (0–9 mm) rather than further into the sediment (9–13 mm). Greater sampling resolution would be required to determine whether a thin oxygenated surface layer (of either the vertical or radial plane) exists in which denitrification is inhibited. Although this study accurately demonstrates the spatial effect of C. aequisetis on sediment potential denitrification, the reported denitrification intensity may not reflect the rate in situ.