Anammox and Denitrification in Marine Environments

The discovery of anaerobic ammonium oxidation (anammox) in natural systems has fundamentally changed our understanding of the global nitrogen cycle. Anammox is an alternative mechanism of denitrification, whereby biologically available N is returned to the atmosphere. Quantifying rates and investigating the differential regulation of anammox and denitrification is relevant to understanding how marine ecosystems will respond to environmental change. We have recently initiated studies to investigate anammox and denitrification rates using ¹⁵N isotope pairing techniques in the world’s major oxygen minimum zones (OMZs), in the Arabian Sea and Eastern Tropical Pacific, where globally significant biological N loss occurs. Our data suggests that anammox activity is favored at the top of the OMZ in open ocean waters (see figure). The relative contribution of anammox and denitrification in the world’s OMZs remains controversial, however, and we are currently investigating novel techniques to measure anammox and denitrification rates in the water column, in comparison with previously published methods. We have also investigated anammox and denitrification activities in estuarine and marine sediments (Chesapeake Bay and Peru margin), and found that anammox contributes more to N₂production in marine than in estuarine sediments.