Stark Contrast in Denitrification and Anammox across the Deep Norwegian Trench in the Skagerrak

Abstract

Environmental anaerobic ammonium oxidation (anammox) was demonstrated for the first time in 2002, using 15 N labeling, in homogenized sediment from the Skagerrak, where it accounted for up to 67% of N 2 production. We returned to some of these original sites in 2010 to make measurements of nitrogen and carbon cycling under conditions more representative of those in situ, quantifying anammox and denitrification, together with oxygen penetration and consumption, in intact sediment cores. Overall, oxygen consumption and N 2 production decayed with water depth, as expected, but the drop in N 2 production was relatively more pronounced. Whereas we confirmed the dominance of N 2 production by anammox (72% and 77%) at the two deepest sites (ϳ700 m of water), anammox was conspicuously absent from two shallower sites (ϳ200 m and 400 m). At the shallower sites, we could measure no anammox activity with either intact or homogeneous sediment, and quantitative PCR (16S rRNA) gave a negligible abundance of anammox bacteria in the anoxic layers. Such an absence of anammox, especially at one locale where it was originally demonstrated, is hard to reconcile. Despite the dominance of anammox at the deepest sites, anammox activity could not make up for the drop in denitrification, and assuming Redfield ratios for the organic matter being mineralized, the estimated retention of fixed N actually increased to 90% to 97% of that mineralized, whereas it was 80% to 86% at the shallower sites.

Potentially Active Iron, Sulfur, and Sulfate Reducing Bacteria in Skagerrak and Bothnian Bay Sediments

“…They are lower than the total bacterial cell counts (»8.6£ 10 8 cells/g sediment) in the Norwegian trench of SK sediments (see supporting material in reference Trimmer et al 2013). However, the estimates extrapolated in Trimmer et al (2013) could be less accurate than acridine orange and qPCR methods as they are based on NanoDrop measurements.…”

“…They are lower than the total bacterial cell counts (»8.6£ 10 8 cells/g sediment) in the Norwegian trench of SK sediments (see supporting material in reference Trimmer et al 2013). However, the estimates extrapolated in Trimmer et al (2013) could be less accurate than acridine orange and qPCR methods as they are based on NanoDrop measurements. Compared to qPCR gene copy estimates for specific bacterial groups such as anammox bacteria in surface sediments, total bacterial gene copy estimates based on cDNA measurements have not been previously reported for the Baltic Sea or North Sea.…”

Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea Loch: An Integrative In Situ Study

“…Given the relatively high mineralization rates and the dynamic redox condition, most N 2 production in these sediments can presumably be ascribed to denitrification rather than anammox (Rysggard et al 2004;Trimmer et al 2013;Devol 2015). The denitrification rate (2.0 ± 1.1 mmol N m -2 day -1 ), as inferred from the net release of N 2 , is in the high end of available measurements for coastal sediments of similar reactivity (Herbert 1999;Eyre and Ferguson 2009;Devol 2015) and could not be sustained by the relatively moderate NO 3 -uptake from the bottom water (0.43 ± 0.42 mmol N m -2 day -1 ).…”

N2 production through denitrification and anammox across the continental margin (shelf–slope–rise) of the Ulleung Basin, East Sea

“…An additional intriguing geochemical property of the UB surface sediment is the high content of Mn oxides (> 200 μmol cm −3 ; Cha et al ; Hyun et al ) that supports a large contribution of Mn reduction to C org oxidation (45% of total; Hyun et al ). Manganese oxides have previously been suggested to influence benthic nitrogen transformations either directly through ammonium oxidation (Luther et al ) or by favoring anammox due to competive inhibition of denitrification by Mn reduction (Thamdrup and Dalsgaard ; Trimmer et al ). Yet the role of Mn as a controlling factor for N cycling remains poorly understood.…”