Shift from denitrification to anammox after inflow events in the central Baltic Sea

Hannig, M., G. Lavik, M. M. M. Kuypers, D. Woebken, W. Martens-Habbena, K. Jürgens

Limnol. Oceanogr., 52(4), 2007, 1336-1345 | DOI: 10.4319/lo.2007.52.4.1336

ABSTRACT: Incubation experiments with 15N-labeled compounds (NO3- and NH4+) were performed during three cruises (2002, 2004, and 2005) to study the loss of inorganic N as dinitrogen gas (N2) via denitrification and anammox in the water column of the Gotland Deep (central Baltic Sea). 15N incubations did not provide evidence for direct conversion of NO3- reduction to N2 (heterotrophic denitrification) in the suboxic (O2 < 10 µmol L-1) sulfide-free waters. Substantial denitrification rates (up to 2.7 µmol L-1 d-1 N2) were measured in water samples collected from the NO3--H2S interface (redoxcline) in 2002 and in water from the sulfidic zone in 2004, which indicates chemolithotrophic denitrification as the dominant N-loss process in both years. Massive inflows of oxygenated North Sea water from 2002 to 2003 caused a complete ventilation of the Baltic Sea with high oxygen concentrations in the Gotland Deep bottom water. After the reestablishment of the redoxcline in 2004, a newly formed suboxic zone above sulfidic waters—with NO3-, NO2-, and NH4+ at the detection limit—was observed in spring 2005. The development of this zone was associated with a several-fold increase in reduced and oxidized manganese and with a shift from denitrification to anammox as the main N-loss process. Fluorescence in situ hybridization analysis confirmed the presence of anammox bacteria and the number of anammox cells was consistent with the observed N2 production rates in 2005.

Article Links

Please Note