Aspects of nitrogen and carbon cycling in the northern Bering Shelf sediment. I. The significance of urea turnover in the mineralization of NH4+

The impact of macrofauna on nitrogen and carbon mineralization was investigated in sediment of the shallow water Bering Sea Shelf. The main effort was focused on the probable role of macrofauna in the production of urea and the significance of urea turnover in the production of NH,+ Macrofaunal biomass was regulated by the quality and quantity of organic nitrogen available for degradation. This was illustrated by a low macrofaunal biomass in the sediment underlying the low productive Alaska Coastal water and a high macrofaunal blornass below the highly productive Bering Shelf/Anadyr water. A high macrofaunal biomass was correlated with high rates of urea gross production, high concentrations of urea and NH,+, and high sediment-water exchange rates of urea and NHdf. Based on a conceptual model of nitrogen mineralization in the Bering Shelf/Anadyr sediment, it was suggested that urea hydrolysis could b e responsible for u p to 80 % of the gross production of NH4+ The model intimated that a substantial part of the NH4+ produced (44 %) could have been cycled within the sediment.