144
W. Schramm
Increased pelagic production as a result of eutrophication may have
major effects on the bottom fauna. Increasing deposition of planktonic
organic material, i.e. input of additional energy into the bottom systems,
may result in growing numbers and biomass of the fauna. On the other
hand, it will enhance oxygen-consuming processes, the cause for seasonal oxygen deficiency and the occurrence of hydrogen sulphide.
A decline in species number and biomass of the macrozoobenthos, or
even extinction of the bottom fauna during the past 15 years, has been
reported for all deeper areas of the Baltic, except for the Gulf of Finland,
where the fauna of the deep areas deteriorated in the 1970s. A normal
macrofauna community was, however, re-established in the period
1986-1989. In the northern Kattegat as well as in the Bothnian Bay, the
abundance and biomass of the zoobenthos have increased, probably as a
result of eutrophication. No trend was observed in the shallow areas of
the Aland Sea or in the open Bothnian Sea during this period, however,
macrofauna values are significantly higher compared to the 1920s (HELCOM 1990).
5.5 Changes in the Phytobenthos and Possible Causes
The effects of eutrophication on coastal systems, in particular on
phytobenthic systems, have been well documented in a number of studies around the Baltic. The general picture, mostly derived from comparative studies along the nutrient gradient of receivers (e.g. Wallentinus
1979; Viitasalo 1984; Borum 1985; Funen County Council 1991), may be
summarized as follows.
The primary effect of increasing nutrient levels on benthic vegetation
is enhanced primary production, in particular of fast-growing epiphytic
filamentous algae and green seaweeds (e.g. Pilayella, Ceramium,
Cladophora, Enteromorpha, Monostroma).
The typical plant communities in the shallow waters of the Baltic, the
Fucus belt, seagrass meadows (Zostera), and Chara stands, are reduced
or disappear due to increased competition with fast-growing nutrient
opportunists and epiphytic load. Increased plankton production in the
water column causes greater turbidity and increased sedimentation of
organic matter, which leads to decreasing light penetration. Due to the
changing light climate, the boundaries of depth distribution, e.g. of
Fucus, Laminaria, red seaweeds and seagrass move upward.
W. Schramm
Increased pelagic production as a result of eutrophication may have
major effects on the bottom fauna. Increasing deposition of planktonic
organic material, i.e. input of additional energy into the bottom systems,
may result in growing numbers and biomass of the fauna. On the other
hand, it will enhance oxygen-consuming processes, the cause for seasonal oxygen deficiency and the occurrence of hydrogen sulphide.
A decline in species number and biomass of the macrozoobenthos, or
even extinction of the bottom fauna during the past 15 years, has been
reported for all deeper areas of the Baltic, except for the Gulf of Finland,
where the fauna of the deep areas deteriorated in the 1970s. A normal
macrofauna community was, however, re-established in the period
1986-1989. In the northern Kattegat as well as in the Bothnian Bay, the
abundance and biomass of the zoobenthos have increased, probably as a
result of eutrophication. No trend was observed in the shallow areas of
the Aland Sea or in the open Bothnian Sea during this period, however,
macrofauna values are significantly higher compared to the 1920s (HELCOM 1990).
5.5 Changes in the Phytobenthos and Possible Causes
The effects of eutrophication on coastal systems, in particular on
phytobenthic systems, have been well documented in a number of studies around the Baltic. The general picture, mostly derived from comparative studies along the nutrient gradient of receivers (e.g. Wallentinus
1979; Viitasalo 1984; Borum 1985; Funen County Council 1991), may be
summarized as follows.
The primary effect of increasing nutrient levels on benthic vegetation
is enhanced primary production, in particular of fast-growing epiphytic
filamentous algae and green seaweeds (e.g. Pilayella, Ceramium,
Cladophora, Enteromorpha, Monostroma).
The typical plant communities in the shallow waters of the Baltic, the
Fucus belt, seagrass meadows (Zostera), and Chara stands, are reduced
or disappear due to increased competition with fast-growing nutrient
opportunists and epiphytic load. Increased plankton production in the
water column causes greater turbidity and increased sedimentation of
organic matter, which leads to decreasing light penetration. Due to the
changing light climate, the boundaries of depth distribution, e.g. of
Fucus, Laminaria, red seaweeds and seagrass move upward.