83
54 and 62 cm depth is not clear (Fig. 4.41). Fe oxides was reduced below 20 cm
depth. NH4 § concentrations increased rapidly from 0.50 mM at 16 cm depth to 17 mM
at 32 cm depth, indicating a strong SO4 z reduction in this zone. Low concentrations of
Mn 2+, Fe z+, and NH4 + between 0 and 16 cm depth reflect the layer of O2 penetration.
E
E
E
m
-20
0
20
40
6O
80
0
-20
0
2O
4O
6O
80
0
mm
Mn 2+ ()aM)
t00
200
e II
a m
3PO 4 ([aM)
-20,
OI
201
401
601
801
3OO 0
%
NO 3" (mM)
L
t
2
3
NH4 + (raM)
20 F"
40 t
601
801
300 0
I00
200
5
10 15 20
21 !
201
401
601
801
4
0
g
g
Fe2+(mM)
t
2
4.41. Porewater profiles in the sediments of the Elbe River (Hamburg)
In sediments of the major rivers, porewater profiles of NO), Mn 2§ ice 2§ PO43 , and
NI-I,t § are typical of anoxic organic-rich sediments. High input of organic matter in the
sediments of the major rivers are confirmed by the contents of organic carbon of the
sediments. Fig. 4.42).
We did not measure 02 concentrations in the porewater. However, Mn 2§ and NO3"
profiles reflect a complete Oz-eonsumption in the bottom water. Below the sedimentwater-interface, SO42 reduction and methane fermentation are the dominating redox
reactions, indicating a strong anoxic condition in the sediments. This play an
important role in the mobility of nutrients and heavy metals. For example, the
concentration of PO43 in the sediments was probably controlled by the formation of