Environmental Engineering Reference
In-Depth Information
increased with water depth, suggesting that the process was fueled by hydrogen
sulfide. Hydrogen sulfide is the major primary electron donor for the redox
processes in the Mariager Fjord chemocline [46, 83]. Thus, in an extension
of the conclusions from the deepest waters in Golfo Dulce, the results from
Mariager Fjord suggest that anammox is of little importance in systems that
are to a large extent fueled by sulfide oxidation.
Black Sea.
The Black Sea is the world's largest anoxic basin and is a model
for both modern and ancient anoxic environments. It is characterized by a
high ammonium concentration in the deep waters (up to 100 µM), while only
trace amounts of fixed inorganic nitrogen are present in the suboxic zone. This
apparent ammonium sink in the suboxic zone strongly suggests that ammonium
is oxidized anaerobically to N
2
[39, 48, 70]. During an R/V Meteor cruise in
December 2001 the role of anammox in the Black Sea water column was
investigated using microbiological and biogeochemical techniques [35]. Water
samples from various depths were incubated anaerobically after addition of
14
N-
nitrite and
15
N-ammonium to check for anammox activity in the suboxic zone.
The potential anammox activity determined this way showed a clear peak in the
zone of nitrite and ammonium disappearance, whereas no significant anammox
activity was observed outside the suboxic zone. Ladderane' lipids [62] were
used to trace anammox bacteria in particulate organic matter collected from
various depths across the suboxic zone. Three different ladderane lipids were
detected in the saponified total lipid extracts with a depth distribution similar to
that of the potential anammox activity, indicating that anammox bacteria could
indeed be responsible for the anaerobic oxidation of ammonium. Phylogenetic
analysis of the 16S rRNA sequences from Black Sea water at the depth of
maximum ladderane abundance (90 m) confirmed that the Planctomycetes,
tentatively named
Candidatus
Scalindua sorokinii, from the suboxic zone of
the Black Sea are related to bacteria known to be capable of anammox (87.9
% sequence similarity to
Kuenenia
, 87.6% to
Brocadia
) [35]. The sequence
obtained from the Black Sea was nearly identical (98.1%) to a sequence recently
obtained from a bioreactor shown to have anammox activity [58]. Ladderane
biomarkers (Fig. 1) and cells hybridizing with the FISH probe specific for
anammox bacteria were also found in the suboxic zone at the shelf break (Fig.
4; Station 7617, 43 38,04'N 30 02,54'E), indicating that anammox bacteria are
not restricted to the strongly stratified central basin but are also present in the
more dynamic peripheral current [64].
Assuming that the concentration profile of ammonium represents a steady
state, an anaerobic ammonium oxidation rate of
0.007 µM day
−
1
was calcu-
lated for the suboxic zone of the central basin using a reaction diffusion model.
This rate is comparable to aerobic ammonium oxidation rates (0.005-0.05 µM
day
−
1
) determined for the nitrate maximum of the western central basin of
∼
