Long-range transported nutrients and the status of the sugar kelp on the south coast of Norway

A large shift in the coastal marine vegetation, from sugar kelp forest to silty turf algae communities, took place at the Norwegian Skagerrak Coast between 1996 and 2002, after decades of eutrophication and recent climatic events causing elevated sea temperature. The eutrophication of these coastal waters is largely influenced by long-range transported nutrients from the Southern North Sea. The nitrate concentration in the coastal current running along the coast was doubled in 1980-1995 and 75% of the winterspring nitrate originated from the German Bight. Reductions in discharges from the continental rivers are lately reflected in reduced input from long-range transported nutrients and reduced nutrient concentrations in the Norwegian Coastal Current. Modelled results indicate that the 2005 riverine input from Continental rivers, the Kattegat (including the Baltic) and local Norwegian rivers to the affected coastline may have the proportions 45, 25 and 30 %. The Norwegian discharges of nutrients to the south coast of Norway are now of more relative increasing importance than the long-range transported nutrients.