PHOSPHORUS AND NITROGEN
Nutrients that control the growth of plants and algae in the sea. Some species of blue-green algae (cyanobacteria)are able to fixate molecular nitrogen directly from athmosphere, so for them, the amount of soluble phosphorus in the water is decisive.
Nutrient load from the natural environment, independent of the actions of people.
BLUE-GREEN ALGAE I.E. CYANOBACTERIA
A group of photosynthetic bacteria living in aquatic habitats, generating the energy they need by photosynthesis, in the same way as plants do. Massive occurrences of blue-green algae, i.e. Cyanobacteria, are called blooms of blue-green algae. The masses of blue-green algae, which favour high temperatures, are usually at their worst in mid-summer.
The Baltic Marine Environment Protection Commission established four decades ago by the countries surrounding the Baltic Sea: the Commission monitors the status of the Baltic Sea, and gives recommendations on actions required to save the sea. http://www.helcom.fi/
The release of nutrients from the seabed in anoxic conditions, as a result of eutrophication. If transported into surface water layers, nutrients are utilized for algae growth.
LAND BASED LOAD
Nutrient load from land-based sources, e.g. from city wastewaters, industry or agriculture
A plant or animal species for which the Baltic Sea is not the original environment but are transported to the Baltic Sea e.g. with the ballast waters of ships.
NON-POINT SOURCE LOAD
Load originating from several, scattered small sources, e.g.load from agriculture and wastewaters from sparsely populated areas.
Oxygen depletion in the water, occurs especially in water layers near the seabed and the surface of the bottom sediment.
POINT SOURCE LOAD
Load originating from a clearly observable individual source. Examples include wastewaters from industrial plants and cities.
A strong current of ocean water entering the Baltic Sea from the Bothnian Sea via the Danish straits. Can take place only when the weather conditions are propitious,.roughly once in 10 years
Measures taken in the sea environment, to improve the state of the marine environment. Term is also used referring to speeding up the ecological recovery of the Baltic Sea (Vahanen Environment).
In individual cases, the poor status of the seabed can be improved by introducing oxygen to the oxygen-depleted waters close to the seabed. There are two ways to do this: you can pump either air or oxygen-rich surface water to the sea bottom. Oxygenation has been used in lake rehabilitation for quite some time already. In the Baltic Sea, however, the scale of the operation is completely different if the goal is to have an impact also on areas other than the closed-off sea bays.
RETAINING PHOSPHORUS IN THE BOTTOM SEDIMENT
The top layer sediment of the anoxic, phosphorus-containing seabed can be treated with various substances. The soluble phosphorus in the bottom sediment and the bottom waters can be retained chemically with precipitation mostly performed in the same manner as in wastewater treatment plants, i.e. with aluminium compounds. The method has been used in inland waters, and also tried out in closed-off marine areas in Sweden, for instance in Björnöfjärden.
It is also possible to lower clean clay obtained from dredging to the basins: this could prevent phosphorus release from the sediment both physically and chemically. Calcium carbonate, on the other hand, could retain phosphorus in the same manner as gypsum, which is used in the treatment of cultivated fields. This method has been tried out with good results (references/links to projects: TRAP, NutriTrade, SAVE, Vantaanjoen kipsi). The use and efficiency of various materials for phosphorus retention in a marine environment has not, however, so far been studied, with the exception of treatment with aluminium. The use of calcium carbonate in the Baltic Sea will be tested for the first time in next year’s SEABASED project.
REHABILITATION OF THE BOTTOM SEDIMENT
The bottom sediment can in principle be removed with normal bucket or suction dredging. In Sweden, however, a removal method has been developed for the bottom sediment’s top layer, which contains copious amounts of organic, oxygen-consuming material; with the method, only approx. 2 cm of sediment from the top is suctioned, without mixing the seabed. The method has been tried out in Swedish lakes, and also in small-scale pilots in the Baltic Sea, at a depth of 120 m.
Nutrients can also be removed from the sea with biomass. Fish stock management through the fishing of predominantly cyprinid fish, a method we know from internal waters, is one approach that is being developed in Finland with the goal of making it also commercially viable (reference/link: Nutritrade, Pilot Fish / Local Fishing Project). Growing blue mussels and using them e.g. as fertilizer or feed is ongoing as an extensive trial, taking place mostly in the southern parts of the Baltic Sea (reference/link: Baltic Blue Growth, NutriTrade Pilot Mussel). Also, the algae mass that winds up on the shores can be collected and used in e.g. biogas production.