44
Matisoff et al. (1981), which is maintained by organic and colloidal complexes. In
addition, nucleation may play an important role in the precipitation of calcite.
Conductivity of porewater is an index of ion activity (sum of ion concentrations).
At all sites, conductivity increased correspondingly with depth, reflecting its
association with the mineralization of organic matter (Fig. 4.17)
4.1.8 Phosphorus in the sediments and porewater
In the sediments at Lauffen, after a sharp increase of POa 3" concentrations from 0.003
mM in the bottom water to 0.23 mM at 8 cm depth, the concentrations of PO43"
decreased to about 0.015-0.056 mM. The peak of PO43" concentration (0.16 raM) lay
in 10 cm depth at Wieblingen. At Kochendorf, the maximum PO43- concentration
(0.11 rmM) was found in 30 cm depth (Fig. 4.18).
In the Elsenz River sediments, PO43" concentration increased slowly to 26 cm
depth, and varied between 0.094 and 0.13 mM below this depth. No clear decrease
was found in the sediments. In the Enz River sediments, PO43" increased to a
maximum value (0.21 raM) at 24 cm depth and then decreased to a relatively constant
value (0.10 mM). Similar profiles were found in the Schwarzbach river sediments
(Fig. 4.19).
The contents of particulate P varied between 0.21% and 0.38 % in the sediments at
Lauffen, and 0.12 %-0.51% at Wieblingen. Only 0.10-0.19 % of P was measured in
the sediments at Kochendorf. In the Enz River sediments, P content decreased from
0.32 % at surface sediment layer to 0.15 % at 32 cm depth. Below this depth, it
ranged from 0.17 % to 0.29 % (Fig. 3.18, 3.19).
in natural waters, sedimentation of biologically produced P, biogenic
coprecipitation of P with CaCO3~ and adsorption of P by Fe and Mn oxides account
for the dominant transfer of PO4 " from bottom water to sediments. After deposition
of these particles, PO43" is released not only by the decomposition of organic matter,
but also by the reduction of Fe and Mn oxides (Froelich et al. 1979j Pettersson 1986;
Dahmke et al. 1991; Sundby et al. 1992). Further evidence of PO4 j" release with the
reduction of Fe and Mn oxides was reported by Krom and Bemer (1981). In their
experiment, PO43" was released into the solution during the reduction of ferric iron by
H2S. They found that below the Fe oxide reduction zone, inorganic particulate P
remained constant, while organic P continued to decrease, suggesting a biogenic
source of dissolved PO43" in the porewater.
PO43" and Fe 2+ diffuse towards the surface sediments following the concentration
gradients. At the surface oxic layer, PO43" is readsorbed by freshly formed Fe and Mn
oxides. On the otherhand, the fraction of organic phosphorus decreased with depth
following the decomposition of organic matter. Therefore, P-rich sediment layers
should be expected at the surface sediments, as reported by Krom and Bemer (198 I)
for Long Island Sound sediments, by Balzer (1989) for the Kiel Bight, and by Sundby
et al. (1992) for the Gulf of St. Lawrence. However, such a P-rich surface
Matisoff et al. (1981), which is maintained by organic and colloidal complexes. In
addition, nucleation may play an important role in the precipitation of calcite.
Conductivity of porewater is an index of ion activity (sum of ion concentrations).
At all sites, conductivity increased correspondingly with depth, reflecting its
association with the mineralization of organic matter (Fig. 4.17)
4.1.8 Phosphorus in the sediments and porewater
In the sediments at Lauffen, after a sharp increase of POa 3" concentrations from 0.003
mM in the bottom water to 0.23 mM at 8 cm depth, the concentrations of PO43"
decreased to about 0.015-0.056 mM. The peak of PO43" concentration (0.16 raM) lay
in 10 cm depth at Wieblingen. At Kochendorf, the maximum PO43- concentration
(0.11 rmM) was found in 30 cm depth (Fig. 4.18).
In the Elsenz River sediments, PO43" concentration increased slowly to 26 cm
depth, and varied between 0.094 and 0.13 mM below this depth. No clear decrease
was found in the sediments. In the Enz River sediments, PO43" increased to a
maximum value (0.21 raM) at 24 cm depth and then decreased to a relatively constant
value (0.10 mM). Similar profiles were found in the Schwarzbach river sediments
(Fig. 4.19).
The contents of particulate P varied between 0.21% and 0.38 % in the sediments at
Lauffen, and 0.12 %-0.51% at Wieblingen. Only 0.10-0.19 % of P was measured in
the sediments at Kochendorf. In the Enz River sediments, P content decreased from
0.32 % at surface sediment layer to 0.15 % at 32 cm depth. Below this depth, it
ranged from 0.17 % to 0.29 % (Fig. 3.18, 3.19).
in natural waters, sedimentation of biologically produced P, biogenic
coprecipitation of P with CaCO3~ and adsorption of P by Fe and Mn oxides account
for the dominant transfer of PO4 " from bottom water to sediments. After deposition
of these particles, PO43" is released not only by the decomposition of organic matter,
but also by the reduction of Fe and Mn oxides (Froelich et al. 1979j Pettersson 1986;
Dahmke et al. 1991; Sundby et al. 1992). Further evidence of PO4 j" release with the
reduction of Fe and Mn oxides was reported by Krom and Bemer (1981). In their
experiment, PO43" was released into the solution during the reduction of ferric iron by
H2S. They found that below the Fe oxide reduction zone, inorganic particulate P
remained constant, while organic P continued to decrease, suggesting a biogenic
source of dissolved PO43" in the porewater.
PO43" and Fe 2+ diffuse towards the surface sediments following the concentration
gradients. At the surface oxic layer, PO43" is readsorbed by freshly formed Fe and Mn
oxides. On the otherhand, the fraction of organic phosphorus decreased with depth
following the decomposition of organic matter. Therefore, P-rich sediment layers
should be expected at the surface sediments, as reported by Krom and Bemer (198 I)
for Long Island Sound sediments, by Balzer (1989) for the Kiel Bight, and by Sundby
et al. (1992) for the Gulf of St. Lawrence. However, such a P-rich surface