BALLAST WATER EXCHANGE AREAS. Prospects of designating BWE areas in the Baltic Proper

Typ: Rapport
Serie: Oceanografi 85
Författare: Pia Andersson


Investigations were made to find out if there are areas with suitable environments for ballast water exchange. Suitable conditions may be areas of certain depths (preferably >200 meters) or distance from the coast (preferably >200nm or >50nm). 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. There is a high possibility that the surface waters in the BWE areas can be transported to protected areas or the coast and with a prevailing wind of 15 m/s it can take one day to one week, depending on the wind direction. 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 omparing 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.