The Baltic Sea and Its Transition Zones
155
198411985. In the following years till 1991, the Fucus populations had
nearly recovered (Carlsson and Gustavsson 1991).
A constant deterioration of the marine environment of the Danish
islands as a result of eutrophication has been observed since the 1960s
and early 1970s. For the waters covering the transition zone between the
Baltic and the Kattegat, a comprehensive report covering the period
1976-1981 was published in 1991 (Funen County Council 1991). As this
report has been quoted in detail in Chapter 7 (Part B. I.), we shall restrict
ourselves to a summarized general picture. The extended seagrass beds
declined to about 50% of the distribution area since the turn of the
century. The lower distribution boundaries of both seagrass and seaweeds have moved upward by 4-5 m, and luxurious growth of filamentous algae is common.
Most affected are the shallow inlets, bays, coves or fjords, subject to
heavily nutrient-loaded land run-off. In extreme cases such as the inner
Odense Fjord, over 5000 ~g dm -'-3 inorganic nitrogen and over 300 ~g
phosphate dm - 3 have been measured. Mass development of sea lettuce
(Ulva lactuca) up to 1020 gm -2 dry weight resulted in extreme daily
oxygen variation, with oversaturation in daytime, oxygen depletion at
night. Release of H 2 S from the sediments occasionally caused the killing
of benethic fauna.
The biological and ecological mechanisms, or the ecophysiological
effects of eutrophication of pollution on macrophytes, which ultimately
lead to the observed changes in the structure of phytobenthic communities, have rarely been studied for the Baltic conditions.
Feldner (1976), for example, investigated the eutrophicating effects of
nutrient components of domestic waste waters on Baltic seaweeds. Productivity and structure of Zostera marina communities in locations with
different eutrophication levels were investigated in Kiel Bight (Feldner
1977).
Studies on the influence of different thallus morphologies on nutrient
uptake suggest that biomass increase and sometimes mass development
of finely branched, filamentous annual algae, which is symptomatic for
eutrophication, are probably the result of competitive advantage of these
forms over the slow growing annual seaweeds, such as Fucus or
Laminaria, due to their capability to take up nutrients more rapidly and
their fast growth (Wallentinus 1984). Also, the much higher uptake rates
of ammonium compared to nitrate nitrogen are probably ecophysiologically relevant, because in eutrophicated water the NH 4 - N concentration is usually higher, compared to unpolluted areas.
Schramm and co-workers (1988) have compared the nutrient requirements and productivity of Fucus vesiculosus and Phycodrys rubens (the
155
198411985. In the following years till 1991, the Fucus populations had
nearly recovered (Carlsson and Gustavsson 1991).
A constant deterioration of the marine environment of the Danish
islands as a result of eutrophication has been observed since the 1960s
and early 1970s. For the waters covering the transition zone between the
Baltic and the Kattegat, a comprehensive report covering the period
1976-1981 was published in 1991 (Funen County Council 1991). As this
report has been quoted in detail in Chapter 7 (Part B. I.), we shall restrict
ourselves to a summarized general picture. The extended seagrass beds
declined to about 50% of the distribution area since the turn of the
century. The lower distribution boundaries of both seagrass and seaweeds have moved upward by 4-5 m, and luxurious growth of filamentous algae is common.
Most affected are the shallow inlets, bays, coves or fjords, subject to
heavily nutrient-loaded land run-off. In extreme cases such as the inner
Odense Fjord, over 5000 ~g dm -'-3 inorganic nitrogen and over 300 ~g
phosphate dm - 3 have been measured. Mass development of sea lettuce
(Ulva lactuca) up to 1020 gm -2 dry weight resulted in extreme daily
oxygen variation, with oversaturation in daytime, oxygen depletion at
night. Release of H 2 S from the sediments occasionally caused the killing
of benethic fauna.
The biological and ecological mechanisms, or the ecophysiological
effects of eutrophication of pollution on macrophytes, which ultimately
lead to the observed changes in the structure of phytobenthic communities, have rarely been studied for the Baltic conditions.
Feldner (1976), for example, investigated the eutrophicating effects of
nutrient components of domestic waste waters on Baltic seaweeds. Productivity and structure of Zostera marina communities in locations with
different eutrophication levels were investigated in Kiel Bight (Feldner
1977).
Studies on the influence of different thallus morphologies on nutrient
uptake suggest that biomass increase and sometimes mass development
of finely branched, filamentous annual algae, which is symptomatic for
eutrophication, are probably the result of competitive advantage of these
forms over the slow growing annual seaweeds, such as Fucus or
Laminaria, due to their capability to take up nutrients more rapidly and
their fast growth (Wallentinus 1984). Also, the much higher uptake rates
of ammonium compared to nitrate nitrogen are probably ecophysiologically relevant, because in eutrophicated water the NH 4 - N concentration is usually higher, compared to unpolluted areas.
Schramm and co-workers (1988) have compared the nutrient requirements and productivity of Fucus vesiculosus and Phycodrys rubens (the