506
til
Q)
20
E 16
~
til
co 12
.....
Q)
"E ::::s 8
Z
4
o
, natural content
:- ----).L. Probst et al.
0,D3 0,3 0,9 1,2 1,8 2,4 2,9 3,3 3,8 4,5 4 ,6 5,4
[Hg] ().Jg g-I)
Fig. 4. Regional natural background of mercury content in river bottom sediments in the III basin
(Data from Collin and Gendrin 1976 and Carbiener 1978)
priori unpolluted areas; but we are not totally sure that these areas have never
been contaminated by mercury pollution in the past.
The differences that can be observed in Fig. 3 between longitudinal mercury
concentration profiles corresponding to different sampling periods could be
attributed to two main factors:
1. The amount of mercury discharged into the Thur river by industrial point
pollution.
2. The climatic and hydrologic conditions of the sampling period, including the
total river suspended sediment concentrations (TSS).
During the high- water period of May 1995, mercury concentrations in the
suspended matter were generally lower than during the high-water periods of
February 1996, in May 1995 the mercury concentration (110 ~lg g- l ) in the
suspended sediments of the industrial wastewater being four times lower than in
February 1996 (438 ~lg g- l). In the Thur river part (until the III confluence), this
difference could not be attributed to a dilution effect of the polluted suspended
sediments by suspended matters coming from slope erosion because the total
suspended sediment concentration is more or less the same during the two
periods (Fig. 5) whereas in the III river part of the system, the dilution effect
contributes to the decrease in mercury content in the sediment because the TSS
concentrations are higher during February 1996 than during May 1995 (Fig. 5).
If one compares mercury concentrations in bottom sediments and in
suspended matter, it is important to note that during the high-water periods
of May 1995 and February 1996 the concentrations are higher in the bottom
sediments than in the suspended matter, whereas during the low-water period of
October 1994, on the contrary, the suspended matter is more concentrated. One
til
Q)
20
E 16
~
til
co 12
.....
Q)
"E ::::s 8
Z
4
o
, natural content
:- ----).L. Probst et al.
0,D3 0,3 0,9 1,2 1,8 2,4 2,9 3,3 3,8 4,5 4 ,6 5,4
[Hg] ().Jg g-I)
Fig. 4. Regional natural background of mercury content in river bottom sediments in the III basin
(Data from Collin and Gendrin 1976 and Carbiener 1978)
priori unpolluted areas; but we are not totally sure that these areas have never
been contaminated by mercury pollution in the past.
The differences that can be observed in Fig. 3 between longitudinal mercury
concentration profiles corresponding to different sampling periods could be
attributed to two main factors:
1. The amount of mercury discharged into the Thur river by industrial point
pollution.
2. The climatic and hydrologic conditions of the sampling period, including the
total river suspended sediment concentrations (TSS).
During the high- water period of May 1995, mercury concentrations in the
suspended matter were generally lower than during the high-water periods of
February 1996, in May 1995 the mercury concentration (110 ~lg g- l ) in the
suspended sediments of the industrial wastewater being four times lower than in
February 1996 (438 ~lg g- l). In the Thur river part (until the III confluence), this
difference could not be attributed to a dilution effect of the polluted suspended
sediments by suspended matters coming from slope erosion because the total
suspended sediment concentration is more or less the same during the two
periods (Fig. 5) whereas in the III river part of the system, the dilution effect
contributes to the decrease in mercury content in the sediment because the TSS
concentrations are higher during February 1996 than during May 1995 (Fig. 5).
If one compares mercury concentrations in bottom sediments and in
suspended matter, it is important to note that during the high-water periods
of May 1995 and February 1996 the concentrations are higher in the bottom
sediments than in the suspended matter, whereas during the low-water period of
October 1994, on the contrary, the suspended matter is more concentrated. One