Environmental Engineering Reference
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Although denitrification rates varied in an overall similar manner, they were
less variable than anammox rates in the Thames and more variable in Kat-
tegat/Skagerrak sediments. As a result, the relative contribution of anammox
to N 2 production decreased from 8 to 1% towards the mouth of the Thames,
while it increased from 2 to 79% from the shallowest to the deepest site in
Kattegat/Skagerrak [19, 70, 73]. Overall, the small dataset suggests that anam-
mox is generally of little importance for N 2 production ( < 10%) in nearshore
sediments, while it is more important and may even dominate in open water
sediments (Fig. 2). Some factors controlling the process and its importance
relative to denitrification will be discussed below.
Figure 2. The relative contribution of anammox to N 2 production from anammox plus den-
itrification in marine sediments as a function of water depth (note log scale). Contributions
were determined in jar-type incubations of surface sediment horizons. Measurements from the
Thames estuary were arbitrarily set at 2 m depth. Data from [19, 54, 70, 73].
The existing reports on anammox in sediments are based on experiments
with homogenized sediment from discrete sediment horizons, and rates are re-
ported on a per-volume basis, typically for a sediment horizon that corresponds
only roughly to the anoxic, NO 3 /NO 2 -containing layer where anammox and
denitrification are expected. If the total N 2 flux from the sediment is known,
either from direct measurement (e.g. [13, 61]) or from whole-core incubations
with 15 NO 3 (the isotope pairing technique; [41, 52]), depth-integrated rates
of anammox and denitrification can be estimated by combination of the N 2
flux and the relative importance of the two processes determined in the ho-
mogenized sediment. A whole-core approach for the direct determination of
both anammox and denitrification rates was recently suggested by Risgaard-
Petersen et al. [52]. This approach is a modification of the isotope pairing tech-
nique previously developed for measurement of denitrification in sediments
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