Nitrogen cycling in different types of sediments from Danish waters1

Variations in sediment N:C ratios were correlated with water depth and season. 15NH,+ was used to measure the rates of NH,+ production (d) and incorporation into bacterial cells (i) in sediments from different stations, at different seasons. The validity of the rates d and i was indicated by the predicted correlation of cl:i ratios with N:C ratios of the sediment, and the predicted N:C ratio at which net NH4+ uptake occurred. There was also a correlation between rate cl and product (total NH,+). In the O-2-cm stratum correlations were also established between d, exchangeable NH4+ pool, ratio exchangeable NH?+ : porewater NH4+, flux of NH,+ from sediment, and flux of NH4+ into exchangeable pool. The NO:,- flux from sediment was correlated with nitrification rate and with season. Benthic infauna increased the flux of NHI’ from the sediment by 50%. The rates of transfer of nitrogen (NO,-, NH?+, N,) from sediment to water were 44-66% of the net rates of organic nitrogen mineralization (d - i). Flux of NO,- + NII,+ from the sediment could supply 30-82% of the nitrogen requirement of the planktonic primary producers.