Geoscience Reference
In-Depth Information
2 The dominating water circulation in each basin (the Bothnian Bay, the Bothnian Sea and
the Baltic Proper) constitutes an anticlockwise cell, which distributes the settling particles, the
suspended material and the pollutants in a typical pattern, reflecting the flow of the water (Case
Fig. 4.1c). This anticlockwise cell is created by the rotation of the Earth (the Coriolis force), which
deflects any plume of flowing water to the right in relation to the direction of the flow in the
Northern Hemisphere (and to the left in the Southern Hemisphere). Thus, when a Swedish river
enters the Baltic, the water turns to the right and follows the shore. The net hydrological flow is to
the south on the west (Swedish) side of the Baltic. The currents are rather strong and stable close
to land and weaker towards the centre of each basin. The figure illustrates only the net component
of the flow - this means that the water would also flow in most other directions during the year.
3 A large number of sediment cores have been taken from Baltic accumulation areas and analysed
for EOCl. Case Fig. 4.1d gives results reflecting average conditions. The increase in the EOCl
concentration in the sediments, and hence the increase in sediment and water contamination,
started in the late 1950s and coincides well with the general contamination and increase in
eutrophication in the Baltic.
It should be noted that most of the emissions of EOCl to the Baltic have now been halted as
a result of legislation and public awareness of the problem. The Baltic is recovering from this
contamination. The time perspective of this recovery can be illustrated using the sediment data
in Case Fig. 4.1d. It will probably take 20 - 40 years until the system has recovered so that the
EOCl concentration in surficial sediments is back to the 'normal' values that characterized the
system about 50 years ago.
This example illustrates the very close and important connection between pollution site and
load, distribution of pollutants by water currents, which regulate where high and low contamina-
tion appears, and hence also where small and large potential ecosystem effects may be expected.
This also shows that different contaminants from the same pollution site often (as in this case)
are distributed in the aquatic environment together, because the distribution depends on the
fact that both the dissolved and the particulate forms of the pollutants are distributed by the
same hydrodynamic and bottom-dynamics processes.
Relevant reading
Södergren A. (Ed.) (1992) Bleached Pulp Mill Effluents. Composition, Fate and Effects in the Baltic Sea. Report
4047, Swedish Environmental Protection Agency, Stockholm, 150 pp.
conditions. Case Study 4.2 sets out an example
of climate change impacts upon Lake Batorino,
Belarus.
regarded as a tape-recorder of the lake's histor-
ical development and are often called 'the geo-
logical archive' (Zolischka 1998; Hammarlund
et al. 2003). The sediments also affect the condi-
tions in the water via, for example, resuspension
processes and by the fact that the animals living
in the sediments play a fundamental role in
the ecosystem (Fig. 4.5). By extracting sediment
cores and conducting a number of analyses,
information is obtained on changes that have
taken place in the ecosystem (Thomas et al. 1976;
4.4
SEDIMENT DATING AND SEDIMENT RECORDS
4.4.1 Sediment dating using radionuclides
The sediments reflect what is happening in the
water mass and on the bottom - they may be
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