37
is large. Despite a high rate of S042- reduction, there is still sufficient labile organic
matter present after SO42" depletion to support CH 4 fermentation. In the Elsenz River,
where SO42- reduction process occurred throughout the sediment core, only slight
'increase of NI-I,~ + was measured in the sediments, which was probably resulted from
SO42" reduction.
The decomposition rate of organic matter depends on the availability of labile
organic matter in the sediments. Since the availability of labile organic matter
decreases with depth, an increase of the decomposition rate might be observed only in
the uppermost sediment layer. This may explain the similar NH4 + profile from
different seasons at site Lauffen.
4. i.7 Alkalinity, Ca, Mg, and conductivity in the porewater
In the sediments of the Neckar River, alkalinity increased rapidly with depth at sites
Lauffen and Wieblingen. The maximum values were 44 meq/l (at 78 cm) at Lauffen,
and 33 meq/1 (at 80 cm) at Wieblingen. At Kochendorf, the increase of alkalinity was
slower and the maximum value was 16 meq/1 at 60 cm depth (Fig. 4.12a).
In the Elsenz River, only a slight increase of alkalinity was identified in the
sediments. The maximum value (8.4 meq/l) was measured at 58 cm depth. In the Enz
River, the maximum value (24 meq/1) was found at the deepest sampling depth (Fig.
4.12b). No significant seasonal variation of alkalinity profiles was found in the
sediments at Lauffen (Fig. 4.I2c). Like NH4 + production, alkalinity production can
be separated into two zones: in the 8042- reduction zone and in the CH 4 fermentation
zone, indicating the different alkalinity generation processes in the sediments.
The porewater profiles of Ca 2+ and Mg 2 in the sedtments are illustrated in Fig.
4.13 and 4.14. An increase with depth can be observed at all sites. The gradient for
both parameters in the porewater was smallest in the Elsenz River sediments, and
slightly higher in the sediments of the Enz River and Schwarzbach River, whereas the
highest was measured in the Neckar River at Lauffen and Wieblingen. This pattern
coincides with the behavior of NH4 + concentrations and alkalinity. In contrast,
carbonate contents in the sediments of the study area have no clear tendency with
depth. In the sediments at Kocbendorf, 25 % of the carbonate were measured. The
carbonate content was 6.5 % m the Elsenz River sediments and 6.8 % in the Enz
River sediments, respectively. The carbonate contents were lower compared to those
in the Neckar River (Fig. 4.15).
is large. Despite a high rate of S042- reduction, there is still sufficient labile organic
matter present after SO42" depletion to support CH 4 fermentation. In the Elsenz River,
where SO42- reduction process occurred throughout the sediment core, only slight
'increase of NI-I,~ + was measured in the sediments, which was probably resulted from
SO42" reduction.
The decomposition rate of organic matter depends on the availability of labile
organic matter in the sediments. Since the availability of labile organic matter
decreases with depth, an increase of the decomposition rate might be observed only in
the uppermost sediment layer. This may explain the similar NH4 + profile from
different seasons at site Lauffen.
4. i.7 Alkalinity, Ca, Mg, and conductivity in the porewater
In the sediments of the Neckar River, alkalinity increased rapidly with depth at sites
Lauffen and Wieblingen. The maximum values were 44 meq/l (at 78 cm) at Lauffen,
and 33 meq/1 (at 80 cm) at Wieblingen. At Kochendorf, the increase of alkalinity was
slower and the maximum value was 16 meq/1 at 60 cm depth (Fig. 4.12a).
In the Elsenz River, only a slight increase of alkalinity was identified in the
sediments. The maximum value (8.4 meq/l) was measured at 58 cm depth. In the Enz
River, the maximum value (24 meq/1) was found at the deepest sampling depth (Fig.
4.12b). No significant seasonal variation of alkalinity profiles was found in the
sediments at Lauffen (Fig. 4.I2c). Like NH4 + production, alkalinity production can
be separated into two zones: in the 8042- reduction zone and in the CH 4 fermentation
zone, indicating the different alkalinity generation processes in the sediments.
The porewater profiles of Ca 2+ and Mg 2 in the sedtments are illustrated in Fig.
4.13 and 4.14. An increase with depth can be observed at all sites. The gradient for
both parameters in the porewater was smallest in the Elsenz River sediments, and
slightly higher in the sediments of the Enz River and Schwarzbach River, whereas the
highest was measured in the Neckar River at Lauffen and Wieblingen. This pattern
coincides with the behavior of NH4 + concentrations and alkalinity. In contrast,
carbonate contents in the sediments of the study area have no clear tendency with
depth. In the sediments at Kocbendorf, 25 % of the carbonate were measured. The
carbonate content was 6.5 % m the Elsenz River sediments and 6.8 % in the Enz
River sediments, respectively. The carbonate contents were lower compared to those
in the Neckar River (Fig. 4.15).