82
In Weser River sediment, Mn 2§ and Fe z+ were released into porewater directly
below the sediment-water-interface. The concentrations of Mn z+ and Fe z+ increased
continuously with depth. The maximum values were 259 laM for Mn 2§ and 2,09 mM
for Fe 2§ respectively (Fig. 4.40). High NO3" concentration (0.91 - 1.15 raM) in the
bottom water resulted in a rapidly NOs reduction process. Similar to NH4 + profiles in
the Neckar River sediments, steep NI-I4 § concentration gradients between 0 and 30 cm
depth reflects a strong SO4 z reduction process in this zone. Below 30 cm depth, NH4 +
concentration varied between 11.5 and 12.7 raM. Similar to NH~ + profiles, PO42"
concentrations increased continuously between 0 and 30 cm depth, and were constant
(about 60 laM) below 30 cm depth.
.E
o
e"
0
20
40
60
soi
0
ll I
., .
Mn 2+ (I~M)
-201
---;"
01
- o
*
:o I -
oli
601"."
801
NO 3 (raM)
i
100
200
300 0
0.4
0.8
-20
0
1
20 ~
9
1
40
.
60
I
80
P043- (laM)
-20,
,,
I
0 ~ , . .
201
401
601
IIii
9
NH; (raM)
801
0
100
200
300 0
5
10 15 20
-20
0
20
40
60
80
.2
Fe2+(mM)
o
i
Fig. 4.40. Porewater profiles in the sediments of the Weser River (Bremen)
In the Elbe River sediments, a significant release of Mn 2§ into the porewater
occurred below 16 cm depth. NO3 concentrations varied between 0.54 and 0.91 mM
above 52 cm depth. The reason of the high NO3 concentrations (2.2-3.5 raM) between