Nitrogen forms in marine sediment play an important role in its biogeochemical cycling.Up to now,most studies focus on total nitrogen(TN),organic nitrogen(ON) and inorganic nitrogen and could not yield integrated information on nitrogen cycling because different nitrogen forms contributing to their cyclings are different.In this work,nitrogen of Bohai Sea sediment in natural size was divided into transferable and untransferable parts by sequential extraction method for the first time.Estimation of transferable nitrogen and its function in sediment-water exchange showed that the contributions of different nitrogen forms in nitrogen recycling vary on time scale.Estimation indicated that IEF-N and OSF-N exist mostly at the surface of the sediment grain,and act as dominant participator in recycling,IMOF-N and CF-N are mainly present inside the sediment grain and contribute little to recycling.The nitrogen cycling budget for Bohai Sea shows that the contribution of pelagic recycling (74.4%) to primary productivity is much more than benthic recycling(26.1%). Analysis of the correlation between sediment nitrogen and primary production showed that it is very close.IEF-N acts as a “buffer pool” for nitrogen nutrient which can enhance primary productivity.Benthos bioturbation is conducive to enhancement of mineralization,which results in high NH+ 4 and NO- 3 distribution in deep sediments.Contribution of nitrogen forms in recycling varies on time scale.The absolute contribution of each state is consistent with its content in sediment,which has the sequence OSF-N (84.6%)>IEF-N (13.0)> IMOF-N (1.4%)>CF-N (1.0%).Untransferable nitrogen account for 69.15% of TN, among which 49% is due to inclusion in sediment grain interior.
