VTI National Transport Research Database

Vattenområden för skifte av barlastvatten. Möjligheter för att designera vattenområden för skifte i själva Östersjön (Ballast Water Exchange Areas. Prospects of designating BWE areas in the Baltic Proper)

  • Andersson, Pia
  • Sveriges meteorologiska och hydrologiska institut (SMHI), Statlig myndighet, 202100-0696
Sponsors, duration, budget: Naturvårdsverket ; 2006-06-01 -- 2007-02-28 Subject(s): Abstract: I barlastvattenkonventionen är skifte av barlastvatten mellan hamnar ett alternativ till vattenbehandling tills acceptabla vattenbehandlingssystem utvecklats. Denna alternativa behandling gäller endast under en begränsad period. Skifte av barlastvatten är idag den enda möjligheten att minska risken för introduktion av och/eller överlevande av nya främmande arter i ett område. För att vetenskapligt utforska om det är möjligt och biologiskt meningsfullt att designera områden för skifte av barlastvatten i Östersjön evaluerades ett flertal aspekter: 1. Oceanografiska tillstånd; 2. Biologiska tillstånd; 3. Miljötillstånd och viktiga tillgångar: 4. Utsläpp av barlastvatten. Krav och riktlinjer i barlastvattenkonventionen innebär att vattenområden lämpliga för skifte av barlastvatten skall ligga helst >200 nm men minst >50 nm från kusten och ha ett djup av >200 m. I Östersjön finns inga områden >200 nm från kusten eller >50 nm med djup > 200 m. Det finns två områden >50 nm från kusten med djup <200 m. I södra Östersjön finns det största området >50 nm från kusten. Det är också området med den största trafiken. Östersjön är inte så stor och det finns näringsämnen tillgängliga större delen av året. Inget av områdena är idealiskt för skifte av barlastvatten. Områdena är små och ett fartyg måste sänka farten för att kunna genomföra skiftet inom området. Abstract: In the Ballast Water Convention, ballast water exchange (BWE) between ports is an alternative ballast water treatment until acceptable treatment systems have been developed. This alternative treatment is only valid during a temporary time period. Ballast water exchange is today the only chance to reduce the risks of introducing and/or survival of new, alien species in an area. To scientifically investigate if it is possible and biologically meaningful to designate BWE areas in the Baltic Sea, several aspects were evaluated: 1. Oceanographic conditions 2. Biological conditions 3. Environmental conditions and important assets 4. Ballast water discharges. In the Convention, several requirements that should be complied in order to make a BWE are listed. The main requirements are that the BWE zones should be situated >200 nautical miles (nm) from the coast and with a depth of >200meters (m). If there is no such zone along or near the shipping lanes, the BWE zones should be situated >50nm from the coast with a depth of >200m. In the Guidelines on designation of areas for ballast water exchange from the Convention, it is stated that areas of BWE can still be designated even if the stated requirements above do not comply. There are several criteria listed in the Guidelines that need to be considered when designating a BWE area. In the Baltic Sea, there are no areas >200nm from the coast or areas >50nm with depths >200m. There are two areas >50nm from the coast with depths <200m. The main focus is on the southern Baltic Proper since it is the area with the highest traffic, it has the largest of the two existing areas in the Baltic Sea >50nm from the coast. The Baltic Sea is not very large and there are nutrients available most of the year. During spring, the biovolume is at its highest, though there are biological activities (even HABs), mainly to the end of the year. The nutrient level is not low enough to prevent indigenous species survival. The very brackish surface waters vary between 5 psu in the Bothnian Sea to 7 psu in the southern Baltic Proper. The difference between fresh and central Baltic Proper water is not large. There is no definite way to say what specific salinity level will kill the BW organisms since there are many different organisms in the BW. As a rule of thumb, there is always a risk that they may survive. The probability that the surface waters in the BWE areas will reach the nearby protected areas Södra Midsjö bank, Norra Midsjö bank and Hoburgs bank is high. The simulations showed that the discharge could reach the three protected areas within only a few days and coastal areas within 1-2 weeks. Important assets like fish farms can be gravely affected, depending on the contents of the BW. Also competing or predatory species may cause harm, especially in spawning areas of fish or on native species on the sea bed. There are spawning grounds very close to the southern Baltic Proper proposed BWE area. Discharged pollutants normally affect the protected areas. The wave climate in the Baltic Proper is not very rough, especially when comparing to more open sea areas, hence not posing as high risk to the ship or crew safety. The total annual BWE discharge in the southern Baltic Proper is approximated to 1.9*109 m3. Most probably, the uptake of BW in the BWE area will be comprised of previously discharged BW, but at a low concentration. The BWE areas of interest are small. A ship will have to reduce the speed to be able to complete the exchange within the area.
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