Decomposition of Mytilus edulis:: The effect on sediment nitrogen and carbon cycling

The benthic degradation of mussel tissue (Mytilus edulis) was studied in a continuous flow-through system over a 32 day incubation period. Sediment chambers without mussels served as controls. The inflowing artificial seawater and the outflow water were analyzed for dissolved organic nitrogen (DON), short chain fatty acids (SCFA), dissolved inorganic nitrogen (DIN), Sigma CO2 and O-2 during the course of incubation. Sediment profiles of particulate organic carbon (POC), particulate organic nitrogen (PON), total hydrolyzable amino acids (THAA), pore water concentrations of DON and DIN and turnover rate of dissolved free amino acids (DFAA) were measured at four different times during the 32 day experiment. Immediately after the addition of mussel tissue, the chambers became completely anoxic and there was an increase in carbon oxidation and the efflux of DON, SCFA and NH4+ in the from the sediment+mussel layer to the overlaying water. During the first 9 days there was a net buildup of DON, and NH4+ sediment followed by a net consumption of the respective N-species during the remainder of the experiment. During the course of incubation 41% of the organic content of the added mussel tissue was released from the sediment as DON, whereas most of the other mussel-N effluxed the sediment as NH4+. Only 8% of the added mussel-N remained by the end of the experiment. There were indications of stimulated bacterial growth in both the mussel amended and the unamended sediments. This was measured as a net increase in THAA, which could only be explained by net bacterial growth and/or protein synthesis. During mussel decomposition both the estimated bacterial carbon incorporation efficiency and the C:N ratio of the substrates used by the bacteria were low. This resulted in a low bacterial nitrogen demand. As a consequence, almost all of the nitrogen mineralized within the sediment was released to the water column as NH4+. (c) 2005 Elsevier B.V All rights reserved.