Benthic nitrogen cycling in the North Sea

Abstract

We present new data on the rates of sedimentary denitrification and its component processes (canonical denitrification, anammox and dissimilatory nitrate reduction to ammonium) for intertidal and subtidal sites in the North Sea using nitrogen isotope addition methods. We find overall average denitrification rates of 6.3 (range 0.4-10.6) µmol m-2 h-1 , similar to those previously reported for this region and other temperate shelf environments. We find canonical denitrification to be the dominant (>90%) process of the three. At the subtidal sites, most of the denitrification is supported by nitrate generated within the sediments, while at the intertidal site the main source is from the water column. We go on to consider the impact of these rates on nitrogen cycling within the North Sea region and compare the sediment core incubation rate results to estimates derived from modelling approaches. Model rates are somewhat higher than those directly measured and we consider possible reasons for this.

Denitrification, anammox, and DNRA in oligotrophic continental shelf sediments

“…Denitrification rates in the NE New Zealand shelf were lower than those in other Pacific shelves and in the Atlantic Ocean with eutrophic settings. Average rates of surveyed studies in the Pacific of 530 ± 62 μ mol N m −2 d −1 (Christensen et al 2003; Farías et al 2004; Erler et al 2013; Song et al 2016; Na et al 2018; Chang et al 2021; Song et al 2021; Tan et al 2022) and the Atlantic Ocean of 542 ± 139 μ mol N m −2 d −1 (Canfield et al 1993; Lohse et al 1996; Vance‐Harris and Ingall 2005; Trimmer and Nicholls 2009; Fan et al 2015; Sokoll et al 2016; Kitidis et al 2017; Rosales Villa et al 2019) were threefold higher than our rates. In general, it appears that the availability of N sources, in particular NO x − concentrations, can be the potential main driver of denitrification in the majority of these eutrophic shelf sediments (Fig.…”