Nitrogen cycling in different types of sediments from Danish waters1

Abstract

Variations in sediment N:C ratios were correlated with water depth and season.¹⁵NH₄+ was used to measure the rates of NH₄⁺ 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 NH₄+ uptake occurred. There was also a correlation between rate d and product (total NH₄⁺). In the 0–2‐cm stratum correlations were also established between d, exchangeable NH₄+ pool, ratio exchangeable NH₄₄⁺: porewater NH₄+, flux of NH₄⁺ from sediment, and flux of NH₄⁺ into exchangeable pool. The NO₃⁻ flux from sediment was correlated with nitrification rate and with season. Benthic infauna increased the flux of NH₄⁺ from the sediment by 50%. The rates of transfer of nitrogen (NO₃⁻, NH₄⁺, N₂) from sediment to water were 44–66% of the net rates of organic nitrogen mineralization (d − i). Flux of NO₃⁻ + NH₄⁺ from the sediment could supply 30–82% of the nitrogen requirement of the planktonic primary producers.