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Exchange of water to the Baltic occurs primarily through the Öresund
and the Belt. At the Great Belt, a surface current flows through these
inlets and via a 22-25 m deep channel. About 70% of the water that
flows into the Baltic flows via the Great Belt. The Baltic has a volume
of about 21 000 km3 with a little influx of oceanic salt
water. A large influx of freshwater occurs from rain and those rivers that
flow into the Baltic. This influx is about 660 km3 per annum
and this makes the Baltic more or less brackish. Discharge of brackish surface
water from the Baltic is about 960 km3 per annum, while the influx
of salty bottom water via the Great Belt and the Öresund is about 475
km3 per annum.
Excessive influxes of salt water to the Baltic occur only under
extreme circumstances, for example after a long period of strong westerly
winds. Water is then pressed in against the Swedish west coast, while at
the same time Baltic water is pressed to the east allowing a large influx
of salt water through the Great Belt and the Öresund. This infux of
salt water from the North Sea to the Baltic is of vital importance as it
oxygenates the deeper areas that are often affected by severe and protracted
periods of oxygen deficency.
Coastal waters are close to us
Our coasts are important, partly as a source
of income and work and partly for recreation and relaxation. We are many
that use the coastal areas for sailing, diving, bathing and other recreational
activities, but these areas are also of vital importance for fishing, aquaculture
and other related industries. Unfortunately, our coastal areas are plagued
by spills, discharges and other environmental disturbances. The consequences
of these environmental problems vary from area to area, because the size
of the discharges and interference are usually unequally distributed and
because varying winds and currents can either spread or concentrate the
pollutants.
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