170
1. Wallentinus
Rosenberg et al. 1988; Lindahl and Rosenberg 1989). However, most of
the species had recovered within 1 year (Pedersen et al. 1990; J. Karlsson,
pers. comm.). The reason for the bloom will probably never be fully
clarified (Graneli et al. 1993) and climate, nutrients, trace elements and
biotic factors may have contributed. The macro algal communities were
also affected indirectly by the large amounts of mussels settling on the
rocks in mainly exposed areas after the bloom, as well as on the
seaweeds. These extensive mussel belts started to disappear to a large
extent during the winter of 1990/1991.
6.2.1 The Swedish Kattegat Coast
Considerable changes in the macro algal communities caused mainly by
eutrophication have occurred in some areas of the southern Kattegat
over the last decades, the most thoroughly studied being those in
Laholm Bay (Wennberg 1987, 1992; Baden et al. 1990; Rosenberg et al.
1990). Other areas along the Kattegat coast have been affected, too,
although less drastically in most areas, except for shallow bays and
harbours. During the last century, there has been an estimated increase
in nitrogen and phosphorus loads in the Kattegat by six and ten times,
respectively. The nitrogen increase has mainly occurred during the last
25 - 30 years, while the phosphorus load during that period showed a
slight decrease (e.g. Rosenberg et al. 1990). An annual load of about
81 000 tonnes of total nitrogen and 3100 t of total phosphorus has been
estimated to enter the Kattegat (cf. Fig. 6.1), including 26 000 t of nitrogen from the atmosphere (data reported to the Helsinki Commission as
quoted in Anonymous 1991). Other sources in the same publication
report values about twice as high.
Laholm Bay. This bay in the southern Kattegat has been much studied
from several aspects, and the nutrient loads from land, atmospheric
deposition and exchanges with the deep water and the Baltic Sea are well
documented (Rosenberg et al. 1990; Rydberg et al. 1990 and references
therein). The nitrogen load from land to Laholm Bay amounts to an
average of about 5000 t total nitrogen (ca. 50% inorganic nitrogen) per
year (Joelsson and Stilbe 1993), which to a very high extent depends on
land runoff from agriculture (ca. 40%) but also to an increasing extent
from leakage from forested areas (ca. 40%), while sewage has been estimated to contribute with around 15%. On top of that comes the atmospheric deposition, which amounts to roughly 10-15% of the total load
from land. In addition, around 20% of the nitrogen is estimated to
1. Wallentinus
Rosenberg et al. 1988; Lindahl and Rosenberg 1989). However, most of
the species had recovered within 1 year (Pedersen et al. 1990; J. Karlsson,
pers. comm.). The reason for the bloom will probably never be fully
clarified (Graneli et al. 1993) and climate, nutrients, trace elements and
biotic factors may have contributed. The macro algal communities were
also affected indirectly by the large amounts of mussels settling on the
rocks in mainly exposed areas after the bloom, as well as on the
seaweeds. These extensive mussel belts started to disappear to a large
extent during the winter of 1990/1991.
6.2.1 The Swedish Kattegat Coast
Considerable changes in the macro algal communities caused mainly by
eutrophication have occurred in some areas of the southern Kattegat
over the last decades, the most thoroughly studied being those in
Laholm Bay (Wennberg 1987, 1992; Baden et al. 1990; Rosenberg et al.
1990). Other areas along the Kattegat coast have been affected, too,
although less drastically in most areas, except for shallow bays and
harbours. During the last century, there has been an estimated increase
in nitrogen and phosphorus loads in the Kattegat by six and ten times,
respectively. The nitrogen increase has mainly occurred during the last
25 - 30 years, while the phosphorus load during that period showed a
slight decrease (e.g. Rosenberg et al. 1990). An annual load of about
81 000 tonnes of total nitrogen and 3100 t of total phosphorus has been
estimated to enter the Kattegat (cf. Fig. 6.1), including 26 000 t of nitrogen from the atmosphere (data reported to the Helsinki Commission as
quoted in Anonymous 1991). Other sources in the same publication
report values about twice as high.
Laholm Bay. This bay in the southern Kattegat has been much studied
from several aspects, and the nutrient loads from land, atmospheric
deposition and exchanges with the deep water and the Baltic Sea are well
documented (Rosenberg et al. 1990; Rydberg et al. 1990 and references
therein). The nitrogen load from land to Laholm Bay amounts to an
average of about 5000 t total nitrogen (ca. 50% inorganic nitrogen) per
year (Joelsson and Stilbe 1993), which to a very high extent depends on
land runoff from agriculture (ca. 40%) but also to an increasing extent
from leakage from forested areas (ca. 40%), while sewage has been estimated to contribute with around 15%. On top of that comes the atmospheric deposition, which amounts to roughly 10-15% of the total load
from land. In addition, around 20% of the nitrogen is estimated to