Coastal eutrophication: Causes, consequences and perspectives in the Archipelago areas of the northern Baltic Sea

Coastal eutrophication has, since the early 1970s, become the foremost threat to the marine ecosystem of the Archipelago Sea (the Åland Islands and the SW Finnish archipelago) in the northern Baltic Sea. Nutrient levels (N, P) have risen significantly both in coastal areas and basin-wide, which has led to increased primary production (both pelagic and benthic), decreased transparency, increasing amounts of oxygen-consuming drift-algal mats at shallow and intermediate bottoms, and changes in zoobenthos and fish communities. Local nutrient input originates mainly from agriculture, riverine input, municipal wastewaters, aquaculture and airborne loading. Levels indicate an even distribution of nutrients from the inner areas to the open coast, reducing the natural diluting or filtering effects of the mosaic archipelago system. Future prospects for the archipelago and coastal ecosystem are poor unless local and regional measures to drastically reduce nutrient levels of the archipelago are undertaken. Even then, positive effects are unlikely to show immediately.