1 Abstract
Major rivers within Germany (Rhine, Neckar, Main, Weser, and Elbe) drain densely
populated and important industrial areas. The rivers had been polluted with heavy
metals and organic pollutants by industrial and municipal emissions mainly before
1970 or - in the case of the Elbe - before 1990.
An important ecological problem still exists in the high heavy metal concentration
of the river sediments. To assess the risk of heavy metal remobilization from
sediments, porewater and sediment samples were examined from 10 sites in these
rivers. For comparison porewaters from Lake Constance were also analyzed. Further
investigations were carried out on sediment profiles of the Lean River (China)
draining a hinterland with one of the largest copper mines of the world, and the Oka
River (with its important tributary, the Moscow River) in Russia. The distributions of
Fe, Mn, Cd, Zn, Pb, ~u, Cr, and Co ~ the l~orewat~r and sediments are reported. In
+
3"2+
2+
-
addition, NO3", SO4"-, NH4 , PO4 , Ca , Mg , Br, alkalinity and pH were
determined in the porewaters to study early cl,iagenc, tic processe~.
-
z+
2+
Generally, the depth profiles of NO3 , Mn , Fe , and SO4"- in the sediments are
similar to those reported in other organic-rich sediments: the concentrations of NO3"
2 .
.
.
.
2+
7+ .
and SO4 decrease with depth, whale the concentrations of Mn and Fe increase.
This~ related to the mineralization of organic matter. NO3-, Mn oxide, Fe oxide, and
SO4 - are subsequently reduced during degradation of organic matter. Furthermore,
these reactions occur directly below the sediment-water interface (between 0-20 cm),
suggesting strong anoxic condition in the sediments.
Rates of NO3- reduction appear to depend on temperature. The higher the
temperature, the faster the reaction rate. As the mineralization of organic matter is
mainly biologically catalyzed, higher temperature may result in higher bacteria
activities, and consequently higher degradation rate of the organic matter. In addition,
the availability of labile organic matter and NO 3" has also an effect on the reaction
rates.
During the mineralization of organic matter, Mn 2+ and Fe 2+ are released into the
porewater as a result of the reduction of Mn and Fe oxides. Solubility calculations
indicate that the pore~/ater is suoersaturated in respect to rhodochrosite (MnCO3) and
2+
2+
siderite (FeCO3). Mn
and Fe seem to I~ controlled by the formation of Mn and
Fe carbonate in the anoxic porewater. Mn2+and Fe 2+ diffuse upward due to their
concentration gradients. They are reoxidized and precipitated as Mn and Fe oxides in
the oxic surface layer. However, significant accumulations of particulate Mn and Fe
in the surface sediments have not been found. This can be attributed to high geogenic
Fe and Mn concentrations already existing in the sediments. In addition, mixing
processes of the sediments by bioturbation and/or resuspension might prevent an
enrichment.
+
As products of the mineralization of organic matter, the concentrations of NH4
and alkalinity increase with depth. They are very different at different sites due to
+
different intensity of organic matter decomposition. In most cases, NH4 and
Major rivers within Germany (Rhine, Neckar, Main, Weser, and Elbe) drain densely
populated and important industrial areas. The rivers had been polluted with heavy
metals and organic pollutants by industrial and municipal emissions mainly before
1970 or - in the case of the Elbe - before 1990.
An important ecological problem still exists in the high heavy metal concentration
of the river sediments. To assess the risk of heavy metal remobilization from
sediments, porewater and sediment samples were examined from 10 sites in these
rivers. For comparison porewaters from Lake Constance were also analyzed. Further
investigations were carried out on sediment profiles of the Lean River (China)
draining a hinterland with one of the largest copper mines of the world, and the Oka
River (with its important tributary, the Moscow River) in Russia. The distributions of
Fe, Mn, Cd, Zn, Pb, ~u, Cr, and Co ~ the l~orewat~r and sediments are reported. In
+
3"2+
2+
-
addition, NO3", SO4"-, NH4 , PO4 , Ca , Mg , Br, alkalinity and pH were
determined in the porewaters to study early cl,iagenc, tic processe~.
-
z+
2+
Generally, the depth profiles of NO3 , Mn , Fe , and SO4"- in the sediments are
similar to those reported in other organic-rich sediments: the concentrations of NO3"
2 .
.
.
.
2+
7+ .
and SO4 decrease with depth, whale the concentrations of Mn and Fe increase.
This~ related to the mineralization of organic matter. NO3-, Mn oxide, Fe oxide, and
SO4 - are subsequently reduced during degradation of organic matter. Furthermore,
these reactions occur directly below the sediment-water interface (between 0-20 cm),
suggesting strong anoxic condition in the sediments.
Rates of NO3- reduction appear to depend on temperature. The higher the
temperature, the faster the reaction rate. As the mineralization of organic matter is
mainly biologically catalyzed, higher temperature may result in higher bacteria
activities, and consequently higher degradation rate of the organic matter. In addition,
the availability of labile organic matter and NO 3" has also an effect on the reaction
rates.
During the mineralization of organic matter, Mn 2+ and Fe 2+ are released into the
porewater as a result of the reduction of Mn and Fe oxides. Solubility calculations
indicate that the pore~/ater is suoersaturated in respect to rhodochrosite (MnCO3) and
2+
2+
siderite (FeCO3). Mn
and Fe seem to I~ controlled by the formation of Mn and
Fe carbonate in the anoxic porewater. Mn2+and Fe 2+ diffuse upward due to their
concentration gradients. They are reoxidized and precipitated as Mn and Fe oxides in
the oxic surface layer. However, significant accumulations of particulate Mn and Fe
in the surface sediments have not been found. This can be attributed to high geogenic
Fe and Mn concentrations already existing in the sediments. In addition, mixing
processes of the sediments by bioturbation and/or resuspension might prevent an
enrichment.
+
As products of the mineralization of organic matter, the concentrations of NH4
and alkalinity increase with depth. They are very different at different sites due to
+
different intensity of organic matter decomposition. In most cases, NH4 and