62
Table 4.4. Distribution of Pb in the porewater and sediments (< 20 p.m) of the Neckar l~iver
and its tributaries
Depth
Average
Min.
Max.
Dissolved
cm
mg/kg
mg/kg
mg/k s
Pb n M*
Lauffen
0-20
90
78
100
20-64
210
150
280
Kochendorf
0-22
60
51
67
2.8 (0 cm)
3.8 (2 cm)
4.3 (6 cm)
2.5 (10 era)
2.9 (10 era)
22-60
190
120
290
Wieblingen
0-6
84
80
87
6-32
210
110
300
Elsenz
0-34
80
57
95
Enz
0-22
93
86
100
22-60
250
84
430
2.5 (0 cm)
6.1 (4 cm)
5.0 (6 cm)
3.5 (8 cm)
*Pb could only be detected in some porewater samples, values in brackets indicate the
respective depth.
4.2.4 Zinc
Depth profiles of particulate Zn demonstrate a significant decrease of Zn discharge
since 1973. Exception for the Elsenz River sediments, particulate Zn concentrations
in the older sediment layer doubled those of the younger sediment layer. No
significant difference of particulate Zn was found in the Elsenz River sediments
(Table. 4.5).
Notable peaks of dissolved Zn at the sediment-water interface were measured in the
Neckar River (Fig. 4.28). A sharp decrease of dissolved Zn concentrations was found
between 0 and 20 cm depth. The highest concentration of dissolved Zn (3.1 x 103 nM)
was measured at the sediment-water interface in the Enz River. The concentrations of
Zn decreased dramatically to 130 nM at 6 cm depth and remained at a fairly low level
(60-100 n.M). Low concentrations of dissolved Zn were measured in the bottom water
of the Schwarzbach River and Elsenz River. Within the sediments they also decreased
with depth (Fig. 4.29).