,13
the porewater at Lauffen confirm this mechanism (Fig. 4.16). Calcite (CaCO3) may
precipitate in the bottom water and deposit in the sediments (Sigg 1986; Sigg et al.
1987).
-10
0
20
4O
E
80
0
~:
0
20
40
6O
8(3
0
Lauffen
9
,,, n
i
89 3
Elsenz
-IC
0
20
40
60
80
0
a. Neckar River
%
%
I
Kochendorf
1
2
3
b. tributaries
-10
o 1
20
".
4o
;
6 0
9149
9
Enz
80
o
i
3
I0
0
2O
4O
6O
8O
4
l
-I0
0
20
40
60
80
4
0
9
Wieblingen
nn9
2
3
4
%
9
1
2
3
4
I
2
3
4
Conductivity (mS/cm)
Fig. 4.17. Conductivity profiles in the porewater of the Neckar River and its tributaries
Since the Ca:Mg ratio in the bottom water is < 2, a formation of dolomite and
magnesite in the bottom water cannot be expected (Miiller et al. 1987). Instead, IowMg calcite might be the predominant precipitate of carbonate. The increase of
dissolved Ca 2§ and Mg z§ in the porewater coincides with the increase of alkalinity.
This demonstrates that iow-Mg calcite in the sediments dissolved through the increase
of CO2, which is released by the mineralization of organic matter. In the sediments of
the study area, porewater is supersaturated with respect to calcite