Dredging stirs up sea bottom along Finnish coast more than gas pipeline would

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Dredging work at Finnish harbours and along shipping routes are stirring up sediments on the sea bottom significantly more than the laying of the planned undersea natural gas pipeline would.
      According to a survey by the Finnish port Association, about seven million cubic metres of earth - a mass 65 times that of the House of Parliament in Helsinki, is to be dredged from the bottom of the sea in the coming years. About a third of it is believed to contain contaminants.
     
The dredging work clouds the surrounding water, and can return nutrients lying on the bottom back into circulation. Although the contaminated layers are peeled away, the digging and moving of the layers oftem means that the toxins are moved to a new location on the sea bottom.
      “The content of harmful materials in the masses that are dumped at sea is very high”, says researcher Seppo Knuuttila of the Finnish Environment Institute. “The masses also do not stay in the area where they are dumped. Instead, they move constantly with the waves.
     
The need for dredging is on the increase, as sea transport is growing; ships are getting bigger, and consequently shipping channels and harbour basins need to be made deeper and wider.
      In Helsinki, harbour areas are being converted to residential use in Jätkäsaari and Sompasaari. This year the biggest project is underway in the West Harbour.
     
More than a million cubic metres of clay and rock are being dredged and blasted from the sea, for the expansion of the harbour, and the rerouting the shipping lanes. Of this amount, 24,000 cubic metres is contaminated with tributyltin (TBT), a toxin used in paint on the hulls of ships.
      The earth that is contaminated with TBT is to be used as filler on land. The non-contaminated earth is to be moved elsewhere in the sea.
      The sea bottom near Helsinki has large amounts of toxic tin compounds. These are a problem in all harbours, because the toxicity of the substances was not noticed until the 1970s.
     
In the Archipelago Sea tin compounds have spread to the Airisto area, where the earth dredged from the bottom of the Turku harbour has been taken. Bottom currents are stronger there than originally thought.
      In Turku there is a great need to dredge the sea, because the Aura River constantly brings sediment to the sea, which settles in shipping channels. However, the sediment that comes with the river flow is relatively clean, as the sources of TBT have been depleted.
     
The permission granted by Finland to lay the gas pipeline that is to run from Russia to Germany through the Finnish economic zone in the sea, is conditional to the use of a vessel that can lay the pipeline without anchors that would stir up the sea bottom. Using the type of vessel that drags anchors behind it would have stirred up the bottom at a width of up to two kilometres.
      At the Russian end of the pipeline route, large amounts of sea bottom are being dredged up, and in the Finnish economic zone, the bottom is being evened out by dropping rocks along the way.
     
Seppo Knuuttila wonders why more attention has not been paid to the dredging and filling activities at Finnish harbours.
      “Near the harbours, the amounts of contaminants are significantly higher than along the pipeline route in the middle of the Gulf of Finland”, Knuuttila notes.
      “The examinations go case by case”, says Mika Seppälä of the Regional State Administrative Agency of Southern Finland, which granted the pipeline company Nord Stream permission to install the pipeline in the Finnish Economic Zones.
      “Although the amounts are greater in the areas near the coasts, and although nutrients and harmful substances certainly are released, the areas are limited in size. the impact of the gas pipeline affects the entire Gulf of Finland.


Previously in HS International Edition:
  Work on gas pipeline to begin in Gulf of Finland in June (15.2.2010)
  Finnish environment groups oppose Baltic Sea gas pipeline (7.1.2010)
  Greenpeace action puts stop to dredging at Pansio harbour in Turku (19.8.2005)

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