Nitrogen cycling in different types of sediments from Danish waters1

Abstract

Variations in sediment N:C ratios were correlated with water depth and season. 1 5 NH 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.