54
4.2 Distribution of heavy metals between sediments and porewater
4.2.1 Copper
Considering the concentrations of particulate Cu in the sediments of the Neckar
River, two zones can be separated: a relatively less polluted layer and a heavily
polluted layer (Table 4.2). The interface between the two zones lay at 20 cm depth at
Lauffen and 22 cm depth at Kochendorf (Fig. 4.24). At Wieblingen, the younger, less
polluted sediment layer was located between 0 and 6 cm due to a removal of sediment
by high water discharge. High concentrations of particulate Cu were measured in the
Enz River sediments below 22 cm depth. The average value in the Elsenz River
sediments was 87 mg/kg, No significant difference with depth was found through the
sediment core (Fig. 4.25).
Table 4.2. Distribution of Cu in the sediments (< 20 lam) of the Neckar River and its
tributaries
Depth
Average
Min.
Max.
....
cm
m~/kg
m~/k s
mg/kg
Lauffen
0-20
96
89
110
20-64
320
200
430
Kochendorf
0-22
56
46
61
22-60
140
100
170
Wieblingen
0-6
78
74
79
6-32
150
72
230
Elsenz
0-34
87
48
120
Enz
0-22
170
150
200
22-60
360
160
560
The high concentrations of Cu in the sediments did not coincide with a release of
dissolved Cu into the porewater. Maximum values of dissolved Cu (53-210 riM) were
measured at the sediment-water interface in the Neckar River. A sharp decrease of the
dissolved Cu was identified below the interface. In the older sediment layer with
higher concentrations in particulate Cu, dissolved Cu was less than or equal to 5 n.M
(Fig. 4.24).
A remarkable peak of dissolved Ca (350 aM) was found at the sediment-water
interface in the Enz River. In the Elsenz River and the Schwarzbach River, the
dissolved Cu concentrations were higher in the overlying water than in the porewater
(Fig.4.25). The rapid decrease of Cu in the porewater with depth occurred below the
sediment-water interface.