Environmental Engineering Reference
In-Depth Information
above 35
◦
C [12, 54]. The increase in rate with increasing
in situ
temperature
corresponded to Q
10
-values of 2.2 - 2.5. Denitrification was more favored by
higher temperatures and the relative importance of anammox in N
2
production
decreased continuously with increasing temperature above 6
◦
C.
Short-term temperature responses reflect the physiology of the active micro-
bial community and cannot be used to predict or interpret changes in activity in
response to, e.g., seasonal temperature variations, or between sites with differ-
ent temperatures. However, the results indicate differences between the natural
anammox community and the well-studied anammox population of wastewater
systems, which has an optimum temperature of 37
◦
C [65]. Viewed together,
the results suggest that the distribution of anammox activity in the environment
will not be excluded by temperatures between freezing and 40
◦
C.
5.2 Organic Matter
The activity of anammox bacteria in the environment may not be directly
dependent on the availability of organic compounds if they are capable of
autotrophy, as are those known from wastewater systems [59]. The recent
demonstration of acetate and propionate oxidation coupled to nitrate and/or
nitrite reduction by anammox bacteria from wastewater bioreactors shows,
however, that organic matter cannot be excluded as either carbon or energy
source for anammox bacteria in the marine environment [26].
While direct use of organic matter by anammox bacteria needs further ex-
ploration, it is clear that organic matter is the main source of NH
4
+
through
ammonification. This likely explains the general correlation of anammox rates
and sediment metabolism, as an indicator or organic carbon availability, ob-
served in sediments (see above). It has also been suggested that a correlation of
anammox with organic content of the sediment was caused by NO
2
−
availabil-
ity, with greater reductive NO
2
−
production in more C
org
-rich sediments [73].
Nitrite is, however, only an intermediate in the reduction of NO
3
−
to N
2
or
NH
4
+
, and NO
2
−
consumption through these pathways could also be expected
to be stimulated with increased availability of organic substrates. Further as-
pects of interactions between anammox bacteria and NO
3
−
/NO
2
−
reducers are
discussed below.
The Black Sea and Golfo Dulce exemplify wide differences in the tightness
of coupling between anammox and ammonification. In the Black Sea, anammox
is an interface process fueled by NH
4
+
transported from the deeper basin, and
largely independent of local sources [35]. In much of the water column in Golfo
Dulce, anammox is NH
4
+
-limited and tightly coupled to the local mineralization
of organic N [11]. In sediments, both these situations are possible, and in a given
environment the NH
4
+
source may fluctuate over time between local sources
