Denitrification and anammox activity in Arctic marine sediments

Abstract

We measured rates of N2 production through anaerobic NH4+ oxidation with NO2−(anammox) and denitrification in permanently cold (from −1.7°C to 4°C) sediments off the east and west coasts of Greenland. The investigated sites (36– to 100–m water depth) covered sediments in which carbon contents ranged from 0.3 to 3.2 dry weight %, O2 uptake rates ranged from 3.4 to 8.3 mmol m−2 d−1, O2 penetration depths ranged from 0.25 to 1.70 cm, and bottom‐water NO3−concentrations ranged from 0.3 to 15.3 µmol L−1. Total N2 production was 34–344 µmol N m−2 d−1, of which anammox accounted for 1–92 µmol N m−2 d−1 (1–35% of total) and denitrification for 33–265 µmol N m−2 d−1. At one of the high‐Arctic sites, anammox activity had an optimum temperature (Topt) of 12°C, while that of bacterial denitrification was 24°C. According to the classical temperature scheme for metabolic growth, the anammox response was psychrophilic, while denitrification was psychrotrophic. Although Topt was considerably higher than in situ temperatures, rates of denitrification and anammox were still high at −1.3°C, reaching 17% and 40%, respectively, of those found at Topt. The activation energies, Ea, of anammox and denitrification were 51.0 and 60.6 kJ mol−1, respectively, and the corresponding Q10 values were 2.2 and 2.4. Rates of anammox were linearly correlated with bottom‐water NO3−concentrations (r2 = 0.96, p < 0.0001, n = 11) at the investigated sites. We suggest that the slow‐growing anammox bacteria are favored in sediments with high and stable NO3−conditions. This may be a general pattern in deeper waters at other latitudes as well.