93
4 % in the Neckar River sediments, indicating low input of organic matter to the
sediment as a result, little concentration gradients were found in the sediments (Fig.
4.50). Mn 2§ was released below the sediment-water-interface. NO3" in the overlying
water was only 0.056 mM compared to 0.40 rmM in the Neckar River water. Fe 2"
increased from 36 ~M at 20 cm depth to 290 p,M at 65 cm depth. The maximum
value of PO43 (50 ~tM) was measured at 5 cm depth. As an indicator of the
mineralization of organic matter, alkalinity increased with depth. The maximum value
was only 6.6 meq/l compared to 43 meq/t in the Neckar River sediments. Dissolved
organic carbon (DOC) increased from 0.67 mM in the supernating water to 2.1 mM at
57 cm depth. This can be attributed to the decomposition of organic matter. In
addition, Eh values were negative below 10 cm depth, reflecting O2-consumption by
the mineralization of organic matter.
4.4.3. Mobility of heavy metals in Lean River, P. R. China
In the Lean River sediments (Caijiawan), NO3" concentrations decreased from 0.045
n~l in the overlying water to 0.009 mM at 34 cm depth (Fig. 4.51). This profile was
similar to that in Lake Constance. However, the concentrations of NO3 in the bottom
water were much lower than those in the Neckar River (0.42 mM), indicating a weak
NO3 reduction process. The concentrations of Mn 2~ increased with depth between 0
and 26 cm depth. Fe z' was released into the porewater below 6 cm depth. As a
product of the mineralization of organic matter, NH.~" increased with depth. It is
notable that the maximum value ofNH~ ~ was only 0.47 rmM compared to 3 - 15 mM
in the Neckar River sediments.
Organic carbon content in the sediments of Lean River at Caijiawan was 0.87 %.
Porewater profiles in this river are typical of organic-poor sediments. The profiles of
Mn 2+, Fe -'~, NHa ~, and SO4-'" in the sediments reflect anoxic conditions in the
sediments. This may cause the formation of metal-sufides in the sediments, and
consequently immobility of heavy metals in this aquatic systems.
Fig. 4.52 shows distribution of heavy metals between sediments and porewater. No
significant relationship was found in the concentrations between porewater and
sediments. The concentrations of Cu in the sediments were very high (about 1000
mgfi
As in other anoxic freshwater sediments, transport of heavy metals from the
dissolved to the particulate phase can be explained by the precipitation of metalsulfides. As the carbonate concentrations of the sediments were very low (< 0.2%),
the acid neutralizing capacity of the sediments is low. Therefore, whether the heavy
metals might be released into the overlying water by resuspension of the sediments,
remains an open question.
4 % in the Neckar River sediments, indicating low input of organic matter to the
sediment as a result, little concentration gradients were found in the sediments (Fig.
4.50). Mn 2§ was released below the sediment-water-interface. NO3" in the overlying
water was only 0.056 mM compared to 0.40 rmM in the Neckar River water. Fe 2"
increased from 36 ~M at 20 cm depth to 290 p,M at 65 cm depth. The maximum
value of PO43 (50 ~tM) was measured at 5 cm depth. As an indicator of the
mineralization of organic matter, alkalinity increased with depth. The maximum value
was only 6.6 meq/l compared to 43 meq/t in the Neckar River sediments. Dissolved
organic carbon (DOC) increased from 0.67 mM in the supernating water to 2.1 mM at
57 cm depth. This can be attributed to the decomposition of organic matter. In
addition, Eh values were negative below 10 cm depth, reflecting O2-consumption by
the mineralization of organic matter.
4.4.3. Mobility of heavy metals in Lean River, P. R. China
In the Lean River sediments (Caijiawan), NO3" concentrations decreased from 0.045
n~l in the overlying water to 0.009 mM at 34 cm depth (Fig. 4.51). This profile was
similar to that in Lake Constance. However, the concentrations of NO3 in the bottom
water were much lower than those in the Neckar River (0.42 mM), indicating a weak
NO3 reduction process. The concentrations of Mn 2~ increased with depth between 0
and 26 cm depth. Fe z' was released into the porewater below 6 cm depth. As a
product of the mineralization of organic matter, NH.~" increased with depth. It is
notable that the maximum value ofNH~ ~ was only 0.47 rmM compared to 3 - 15 mM
in the Neckar River sediments.
Organic carbon content in the sediments of Lean River at Caijiawan was 0.87 %.
Porewater profiles in this river are typical of organic-poor sediments. The profiles of
Mn 2+, Fe -'~, NHa ~, and SO4-'" in the sediments reflect anoxic conditions in the
sediments. This may cause the formation of metal-sufides in the sediments, and
consequently immobility of heavy metals in this aquatic systems.
Fig. 4.52 shows distribution of heavy metals between sediments and porewater. No
significant relationship was found in the concentrations between porewater and
sediments. The concentrations of Cu in the sediments were very high (about 1000
mgfi
As in other anoxic freshwater sediments, transport of heavy metals from the
dissolved to the particulate phase can be explained by the precipitation of metalsulfides. As the carbonate concentrations of the sediments were very low (< 0.2%),
the acid neutralizing capacity of the sediments is low. Therefore, whether the heavy
metals might be released into the overlying water by resuspension of the sediments,
remains an open question.