Anaerobic Ammonium Oxidation (ANAMMOX) and Denitrification in Marine Environments (Invited)

Anaerobic ammonium oxidation (anammox) is a newly recognized pathway of nitrogen removal in marine ecosystems, providing a second mechanism to classical denitrification for the net loss of nitrogen. The contribution of anammox and denitrification to dinitrogen production has been investigated in several important regions of nitrogen loss, including the Eastern Tropical South Pacific (ETSP), Arabian Sea, Chesapeake Bay and coastal New England. Based on incubations of homogenized sediments with added 15N-labeled nitrate or ammonium, anammox contributed 0-47% of the dinitrogen production in sediments, while denitrification accounted for the remainder. In estuarine sediments, anammox did not exceed 22% of dinitrogen production. In ocean sediments, anammox accounted for an average of 39% of dinitrogen production in sediments with a water column depth greater than 100m. Denitrification and anammox rates were positively correlated in deeper marine sediments (>100m water column depth), suggesting that anammox and denitrification are coupled in this environment. In Peru margin sediments, Scalindua was the dominant genera of anammox bacteria detected in clone libraries of 16S rRNA and hydrazine oxidoreductase (hzo) gene fragments, which supports the hypothesis that in marine environments Scalindua is the dominant genera. Also based on incubation experiments, anammox and denitrification show large swings in dominance in different pelagic oxygen minimum zones, with anammox completely dominating water column dinitrogen production in the ETSP, but denitrification dominating in the Arabian Sea. The results from sediment and water column studies indicate that the contribution of anammox to dinitrogen production is spatially variable. Although the controls are not well understood, it appears that organic matter deposition rates and nitrate concentrations influence the relative importance of anammox, with anammox being favored under low organic matter deposition rates or relatively high and stable nitrate concentrations.