The Northern Atlantic Coasts
175
6.3 The Border Area Between Sweden and Norway
6.3.1 The Hvaler Area
A joint Swedish-Norwegian study programme was carried out from 1988
to 1990 from Hvaler down to the Koster area in northern BohusHin, with
the aim of clarifying which factors determine the quality of the water in
the outer part of the area. The area is influenced by the large Norwegian
river Glomma (cf. Fig. 6.1), by industrial discharges as well as by water
from the Baltic Current. This programme (with measurements of nutrients, phytoplankton, particles and soft-bottom fauna) did not include
macroalgae. In the early 1980s, Norwegian studies including macro algae
were carried out in the area close to the river outlet (Bokn 1984). Bokn
observed that several macro algae did not occur in the inner area, despite
high nutrient concentrations. This was especially noteworthy for opportunistic green algae such as species of the genera Enteromorpha,
Cladophora and Ulva, whereas cyanobacteria were common. Also Fucus
serratus and Ascophyllum nodosum had disappeared from the area. The
innermost area was then heavily polluted by nutrients, heavy metals and
organic pollutants, while the outer area was only slightly or moderately
polluted (Skei 1984). Also large amounts of silt, particles and humic
substances were brought by the river, influencing the macro algae negatively. Later experimental studies in mesocosms and transplantation
experiments in the field (Bokn 1990) showed that discharged acid waste
from titanium dioxide production was highly detrimental to the macroalgae in the estuary.
6.3.2 The Idefjorden Area
This strongly stratified threshold fjord (thresholds of 8-10 m in the
outer area and a maximum depth around 30-40 m in the fjord) constitutes the border between Sweden and Norway. The upper layer of the
fjord is brackish due to freshwater outflow from the river Tista (for
salinity values see Lein et al. 1974), whereas the bottom water is anoxic.
Since the 1950s, the fjord has also been heavily polluted by discharges
from a paper and pulp mill (dissolved and particulate organic material,
toxic substances) as well as from sewage from the town of Halden and
land runoff from agricultural areas, all of which had strongly reduced the
marine flora and fauna. The macroalgae of the fjord were studied in the
early 1970s (Lein et al. 1974) and in the early 1980s (Rueness et aI.,
175
6.3 The Border Area Between Sweden and Norway
6.3.1 The Hvaler Area
A joint Swedish-Norwegian study programme was carried out from 1988
to 1990 from Hvaler down to the Koster area in northern BohusHin, with
the aim of clarifying which factors determine the quality of the water in
the outer part of the area. The area is influenced by the large Norwegian
river Glomma (cf. Fig. 6.1), by industrial discharges as well as by water
from the Baltic Current. This programme (with measurements of nutrients, phytoplankton, particles and soft-bottom fauna) did not include
macroalgae. In the early 1980s, Norwegian studies including macro algae
were carried out in the area close to the river outlet (Bokn 1984). Bokn
observed that several macro algae did not occur in the inner area, despite
high nutrient concentrations. This was especially noteworthy for opportunistic green algae such as species of the genera Enteromorpha,
Cladophora and Ulva, whereas cyanobacteria were common. Also Fucus
serratus and Ascophyllum nodosum had disappeared from the area. The
innermost area was then heavily polluted by nutrients, heavy metals and
organic pollutants, while the outer area was only slightly or moderately
polluted (Skei 1984). Also large amounts of silt, particles and humic
substances were brought by the river, influencing the macro algae negatively. Later experimental studies in mesocosms and transplantation
experiments in the field (Bokn 1990) showed that discharged acid waste
from titanium dioxide production was highly detrimental to the macroalgae in the estuary.
6.3.2 The Idefjorden Area
This strongly stratified threshold fjord (thresholds of 8-10 m in the
outer area and a maximum depth around 30-40 m in the fjord) constitutes the border between Sweden and Norway. The upper layer of the
fjord is brackish due to freshwater outflow from the river Tista (for
salinity values see Lein et al. 1974), whereas the bottom water is anoxic.
Since the 1950s, the fjord has also been heavily polluted by discharges
from a paper and pulp mill (dissolved and particulate organic material,
toxic substances) as well as from sewage from the town of Halden and
land runoff from agricultural areas, all of which had strongly reduced the
marine flora and fauna. The macroalgae of the fjord were studied in the
early 1970s (Lein et al. 1974) and in the early 1980s (Rueness et aI.,