10 Fixed link Projects in Denmark and Ecological Monitoring of the 0resund Fixed link
113
fifteen are located on Saltholm and twenty are on the Swedish side of the 0resund
(Semac 1997b). The surveying was done partly with a theodolite from the shore and
partly by means of echo sounding from a vessel, with both methods being supplemented
by aerial photography. SedinIent samples were also taken from twenty four of the profiles for analysis of grain size distribution. Data from earlier studies is being compiled
and evaluated in order to compare with the 1996 study to see if any changes of the
coastline have occurred as a result of the construction work.
10.6
Discussion and Conclusions
Spillage from the dredging operations is the most important source of impacts on the
marine environment during the contruction period of the fixed links. The sediment
spill shades vegetation areas in shallow waters and settles on tlIe vegetation and mussels beds. This has potential secondary effects on the feeding resources of breeding
eiders and moulting mute swans and greylag geese on the island of Saltholm. The sediment plumes could also potentially prevent migration of Rugen herring through
0resund when the herring during the autumn and winter period migrate from the
summer feeding areas in Kattegat/Skagerrak to the spring spawning areas along the
German coast in the Baltic Sea.
At the end of December 1996 the Danish and Swedish autlIorities approved nine
dredging instructions and approx. 2.7 million m 3 seabed material was dredged with a
total spill of 4.4% or approx. u8 000 m 3 (Danish Ministry of the Environment and Energy, Danish Ministry of Transport, KSO 1997a). The results from tlIe control and monitoring programme for the first year of the construction period show that the dredging
was performed witlIout exceeding the spill limits and witlIout violation of the environmental quality objectives (Danish Ministry of the Environment and Energy, Danish
Ministry of Transport, KSO 1997a). The oxygen content was relatively high in 1996 and
there was no risk that the construction works caused or increased acute oxygen depletion (Danish Ministry of the Environment and Energy, Danish Ministry of Transport,
KSO 1997a).
The concentration of nutrients above and below the pycnocline was generally lower
in 1996 than in the previous lO-year period. The contribution of nutrients from the
construction works did not lead to a measurable increase in the concentration of nutrients in the water in 1996 (Danish Ministry of the Environment and Energy, Danish
Ministry of Transport, KSO 1997a). By the end of 1996 the changes in the fauna in the
area as a whole did not show a significant reduction in relation to the baseline studies
carried out in 1995, and there is no directional trend in relation to the construction
work.
The investigation of the bentlIic vegetation in 1996 showed a decline in the accessible biomass of tassel pondweed in the area south-west and west of Saltholm witlI tlIe
most affected areas in shallow waters less then 2 m and in areas closest to the construction work. The effects in shallow waters indicate that the decline could be caused by tlIe
severe ice cover during the winter period 1995-1996 while the effect gradient towards
the construction work indicates that the impact is caused by a combination of ice cover
and sediment plumes. Provisonal investigations in 1997 show tlIat the tassel pondweed
has recovered. The accessible biomass of eelgrass in 1996 was comparable with the level
113
fifteen are located on Saltholm and twenty are on the Swedish side of the 0resund
(Semac 1997b). The surveying was done partly with a theodolite from the shore and
partly by means of echo sounding from a vessel, with both methods being supplemented
by aerial photography. SedinIent samples were also taken from twenty four of the profiles for analysis of grain size distribution. Data from earlier studies is being compiled
and evaluated in order to compare with the 1996 study to see if any changes of the
coastline have occurred as a result of the construction work.
10.6
Discussion and Conclusions
Spillage from the dredging operations is the most important source of impacts on the
marine environment during the contruction period of the fixed links. The sediment
spill shades vegetation areas in shallow waters and settles on tlIe vegetation and mussels beds. This has potential secondary effects on the feeding resources of breeding
eiders and moulting mute swans and greylag geese on the island of Saltholm. The sediment plumes could also potentially prevent migration of Rugen herring through
0resund when the herring during the autumn and winter period migrate from the
summer feeding areas in Kattegat/Skagerrak to the spring spawning areas along the
German coast in the Baltic Sea.
At the end of December 1996 the Danish and Swedish autlIorities approved nine
dredging instructions and approx. 2.7 million m 3 seabed material was dredged with a
total spill of 4.4% or approx. u8 000 m 3 (Danish Ministry of the Environment and Energy, Danish Ministry of Transport, KSO 1997a). The results from tlIe control and monitoring programme for the first year of the construction period show that the dredging
was performed witlIout exceeding the spill limits and witlIout violation of the environmental quality objectives (Danish Ministry of the Environment and Energy, Danish
Ministry of Transport, KSO 1997a). The oxygen content was relatively high in 1996 and
there was no risk that the construction works caused or increased acute oxygen depletion (Danish Ministry of the Environment and Energy, Danish Ministry of Transport,
KSO 1997a).
The concentration of nutrients above and below the pycnocline was generally lower
in 1996 than in the previous lO-year period. The contribution of nutrients from the
construction works did not lead to a measurable increase in the concentration of nutrients in the water in 1996 (Danish Ministry of the Environment and Energy, Danish
Ministry of Transport, KSO 1997a). By the end of 1996 the changes in the fauna in the
area as a whole did not show a significant reduction in relation to the baseline studies
carried out in 1995, and there is no directional trend in relation to the construction
work.
The investigation of the bentlIic vegetation in 1996 showed a decline in the accessible biomass of tassel pondweed in the area south-west and west of Saltholm witlI tlIe
most affected areas in shallow waters less then 2 m and in areas closest to the construction work. The effects in shallow waters indicate that the decline could be caused by tlIe
severe ice cover during the winter period 1995-1996 while the effect gradient towards
the construction work indicates that the impact is caused by a combination of ice cover
and sediment plumes. Provisonal investigations in 1997 show tlIat the tassel pondweed
has recovered. The accessible biomass of eelgrass in 1996 was comparable with the level