Environmental Engineering Reference
In-Depth Information
record [62]. For this, however, an assessment of the long-term stability of these
compounds in sediments is needed.
7. ANAMMOX AND THE MARINE NITROGEN
CYCLE
Phytoplankton growth is nitrogen limited in many oceanic regions [9, 20]
due to basin scale imbalances between N
2
-fixation and fixed inorganic nitrogen
(NH
4
+
,NO
2
−
,NO
3
−
) removal by anaerobic microbial activity (Fig. 5). Nutrient
measurements and stable nitrogen isotope modeling indicate that 400-480 Tg
of fixed nitrogen per year is lost from the Ocean, with oxygen minimum zones
and continental margin sediments as the main areas of nitrogen loss [5, 9].
The discovery of anammox as a distinct novel pathway of N
2
production in
marine environments calls for a quantification of its global significance, and an
identification of the main factors that regulate this process.
Figure 5.
Simplified marine nitrogen cycle including the anammox 'sink'; Org. N: organic
nitrogen.
The relative contribution of anammox to the total fixed nitrogen loss as N
2
is still unclear. But the widespread occurrence of anaerobic ammonium oxi-
dation with nitrite to N
2
in marine sediments, anoxic basins and fjords [11,
12, 35, 51, 54, 70, 73] indicates that anammox bacteria could be responsible
for substantial loss of fixed nitrogen from the ocean. Devol [14] argued that
it is possible that anammox accounts for 30-50% of the N
2
production in the
ocean. Theoretically, 29% of the N
2
production during the complete mineral-
