Budgets of sediment nitrogen and carbon cycling in the shallow water of Knebel Vig, Denmark

Sediment was sampled from a shallow coastal area (Knebel Vig.Denmark).The vertical distribution of pigments, Pb-210 and CS-137 indicated that organic matter was muted into the sediment.On an area basis, sediment acid hydrolyzable amino acids accounted for 24 '4, of the particulate organic carbon pool and 53":, of the part~culate organlc nitrogen pool.Similarly, porewater acid hydrolyzable amino acids were an important component of dissolved organic carbon and dissolved organic nitrogen (9 and 27';", respectively).It was inferred that ribonucleic acids potentially were an important component of dissolved organic nitrogen.The estimated efflux of dissolved organic nitrogen from the sediment was higher (3.9 mnlol N m-' d-l) than the estimated efflux of dissolved inorganic nitrogen ( < 2 mm01 N m-' d-l).The high efflux of dissolved organic nitrogen was explained by organic matter hydrolysis close to the sediment surface.The low rates of inorganic nitrogen efflux together wlth a high carbon oxidation rate suggested degradation of organic matter with a low average nitrogen content and possible bacterial nitrogen assimdation.This was further supported by mass balance calculations on nitrogen incorporation into microbial biomass.The calculated average C/N ratio in the organic matter degraded suggested that only part of the sediment acid hydrolyzable amino acids were available for bacterial degradat~on.The efficiency of bacterial carbon incorporation was 0.33 and within the range prev~ously encountered in sediments of Danish waters