An experiment on the relative importance of denitrification, nitrate reduction and ammonification in coastal marine sediment

Abstract

Simultaneous determinations of 15N-nitrogen gas production, 15N-ammonia formation by nitrate reduction and ammonia production from organic nitrogen were carried out after addition of 15N-nitrate to anaerobically incubated sediment slurries from a location in the Dutch Wadden Sea. The rate of nitrogen gas production was 1.57 μmol N·cm −3 wet sediment·d −1, nitrate reduction to ammonia occurred at a rate of 0.79 μmol N·cm −3·d −1 and ammonification at 1.17 μmol N·cm −3·d −1. At the end of the incubation experiment (after 30 h) 63% of the originally added 15N-nitrate was present as nitrogen gas, 32% ended up as ammonia and ∼4% as particulate organic nitrogen. Ammonia production by degradation of organic nitrogen compounds was the most important process in building up the ammonia pool in the anaerobic sediment incubation.