51
before the fish kill in the Schwarzbach River, a lock was opened for repairs. This
resulted in a strong resuspension of the sediment and may have caused a release of
large amounts of O2-depletion substances (NH4 +, Fe2+). Furthermore, NH4 + alone is a
toxic substance for the nerve system of fish. It can lead to muscle cramp, and
consequently fish kill. (Baur 1980).
Normally, the increased 02 demand and high N'H4 t concentrations during flood is
compensated by dilution through the large water runoff, which has no significant
effect on aquatic organisms in the bottom water. It should be noted that both fish kills
( in the Rhine and the Schwarzbach River) occurred in June and April, respectively.
The fish kills did not occur with every flood. In summer, the water level is lower than
in winter, and dissolved O 2 concentrations are lower due to biological O2 demand. As
a result, the buffer capacity of the river for O2 depletion is lower in summer,
especially in a small river such as the Schwarzbach River. Therefore, a resuspension
of the sediments by human activities (e.g. dredging) should be avoided in summer.
The best management for such system would be to stabilize the sediment structure
and to minimize the fluctuation in oxidation-reduction conditions in the sediments.
4.1.10 Sinks or sources of sediments for bromine
At all sites, Br" in the overlying water is below the detection limit (0.25 jaM). The
concentrations of Br" in the porewater showed a tendency to increase with depth. The
gradient of Br" was smallest in the sedunents of the Elsenz River (Maximal value:
0.63 laM), slightly higher in the Schwarzbach River sediments, whereas in the
sediments of the Neckar River exhibited a comparingly high gradient (Fig. 4.22). The
maximal value was 9.26/aM and 9.01 ~aM at Lauffen and Wieblingen, respectively. In
the Ertz River sediments, Br- increased from undetected in the bottom water to a
maximal value of 7.76 p.M at 74 cm depth.
Particulate Br contents in the Neckar River sediments at Lauffen varied between
3.9 and 4.6 mg/kg, which is in agreement with data from freshwater lacustrine
sediments containing Br in the range of 6-18 mg/kg (Mun and Bazilevich 1962).
The Br" profiles were very similar to the profiles ofNH4 + and alkalinity in the same
site. It is well known that the mineralization of organic matter leads to the production
of alkalinity and N]-I4 +, their concentrations are then a measure of the strength and/or
duration of the degradation process, and of the composition and concentration of
organic matter available in the sediments. The very high positive correlation between
Br', NH4 +, and alkalinity leads to the conclusion that bromine, originally a constituent
of the organic matter in the sediments, is released as Br" during early diagenetic
processes (Fig. 4.23).
Only few analyses exist for Br" concentrations in nonmarme plants. Coastal waters
are enriched with CI-IBr 3 and CH2Br 2 due in part to their production by marine
macroalgae and possibly by marine microbes (Manley et al. 1992). Some
organobromine compounds such as CHBr3, CH2Br2, and CHBrC12 were measured in
marine macroalgae tissues (Gschwend et al. 1985) The function of these compounds
before the fish kill in the Schwarzbach River, a lock was opened for repairs. This
resulted in a strong resuspension of the sediment and may have caused a release of
large amounts of O2-depletion substances (NH4 +, Fe2+). Furthermore, NH4 + alone is a
toxic substance for the nerve system of fish. It can lead to muscle cramp, and
consequently fish kill. (Baur 1980).
Normally, the increased 02 demand and high N'H4 t concentrations during flood is
compensated by dilution through the large water runoff, which has no significant
effect on aquatic organisms in the bottom water. It should be noted that both fish kills
( in the Rhine and the Schwarzbach River) occurred in June and April, respectively.
The fish kills did not occur with every flood. In summer, the water level is lower than
in winter, and dissolved O 2 concentrations are lower due to biological O2 demand. As
a result, the buffer capacity of the river for O2 depletion is lower in summer,
especially in a small river such as the Schwarzbach River. Therefore, a resuspension
of the sediments by human activities (e.g. dredging) should be avoided in summer.
The best management for such system would be to stabilize the sediment structure
and to minimize the fluctuation in oxidation-reduction conditions in the sediments.
4.1.10 Sinks or sources of sediments for bromine
At all sites, Br" in the overlying water is below the detection limit (0.25 jaM). The
concentrations of Br" in the porewater showed a tendency to increase with depth. The
gradient of Br" was smallest in the sedunents of the Elsenz River (Maximal value:
0.63 laM), slightly higher in the Schwarzbach River sediments, whereas in the
sediments of the Neckar River exhibited a comparingly high gradient (Fig. 4.22). The
maximal value was 9.26/aM and 9.01 ~aM at Lauffen and Wieblingen, respectively. In
the Ertz River sediments, Br- increased from undetected in the bottom water to a
maximal value of 7.76 p.M at 74 cm depth.
Particulate Br contents in the Neckar River sediments at Lauffen varied between
3.9 and 4.6 mg/kg, which is in agreement with data from freshwater lacustrine
sediments containing Br in the range of 6-18 mg/kg (Mun and Bazilevich 1962).
The Br" profiles were very similar to the profiles ofNH4 + and alkalinity in the same
site. It is well known that the mineralization of organic matter leads to the production
of alkalinity and N]-I4 +, their concentrations are then a measure of the strength and/or
duration of the degradation process, and of the composition and concentration of
organic matter available in the sediments. The very high positive correlation between
Br', NH4 +, and alkalinity leads to the conclusion that bromine, originally a constituent
of the organic matter in the sediments, is released as Br" during early diagenetic
processes (Fig. 4.23).
Only few analyses exist for Br" concentrations in nonmarme plants. Coastal waters
are enriched with CI-IBr 3 and CH2Br 2 due in part to their production by marine
macroalgae and possibly by marine microbes (Manley et al. 1992). Some
organobromine compounds such as CHBr3, CH2Br2, and CHBrC12 were measured in
marine macroalgae tissues (Gschwend et al. 1985) The function of these compounds