Nitrogen cycling in different types of sediments from Danish waters1

Abstract

Variations in sediment N:C ratios were correlated with water depth and season.15NH 4+ was used to measure the rates of NH 4+ 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 d:i ratios with N:C ratios of the sediment, and the predicted N:C ratio at which net NH 4+ uptake occurred. There was also a correlation between rate d and product (total NH 4+). In the 0–2‐cm stratum correlations were also established between d, exchangeable NH 4+ pool, ratio exchangeable NH 44+: porewater NH 4+, flux of NH 4+ from sediment, and flux of NH 4+ into exchangeable pool. The NO 3− flux from sediment was correlated with nitrification rate and with season. Benthic infauna increased the flux of NH 4+ from the sediment by 50%. The rates of transfer of nitrogen (NO 3−, NH 4+, N 2) from sediment to water were 44–66% of the net rates of organic nitrogen mineralization (d − i). Flux of NO 3− + NH 4+ from the sediment could supply 30–82% of the nitrogen requirement of the planktonic primary producers.