Denitrification and anammox activity in Arctic marine sediments

We measured rates of N-2 production through anaerobic NH4+ oxidation with NO2- (anammox) and denitrification in permanently cold (from - 1.7degreesC to 4degreesC) 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 O-2 uptake rates ranged from 3.4 to 8.3 mmol m(-1) d(-1), O-2 penetration depths ranged from 0.25 to 1.70 cm, and bottom-water NO3- concentrations ranged from 0.3 to 15.3 mumol L-1. Total N-2 production was 34-344 mumol N m(-2) d(-1), of which anammox accounted for 1-92 mumol N m(-1) d(-1) (1-35% of total) and denitrification for 33-265 mumol N m(-2) d(-1). At one of the high-Arctic sites, anammox activity had an optimum temperature (T-opt) of 12degreesC, while that of bacterial denitrification was 24degreesC. According to the classical temperature scheme for metabolic growth, the anammox response was psychrophilic, while denitrification was psychrotrophic. Although T-opt was considerably higher than in situ temperatures, rates of denitrification and anammox were still high at - 1.3degreesC, reaching 17% and 40%, respectively, of those found at T-opt. The activation energies, E-a, of anammox and denitrification were 51.0 and 60.6 kJ mo(-1), respectively, and the corresponding Q(10) values were 2.2 and 2.4. Rates of anammox were linearly correlated with bottom-water NO3- concentrations W = 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.