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Today, phosphorus is regarded as the key nutrient for Baltic Sea eutrophication
management. Major sources are large rivers like the Oder, Vistula, Daugava in the
southern Baltic region. Before entering the Baltic Sea, these rivers discharge their
nutrient load into coastal estuaries, bays and lagoons. The quantitative role of
these coastal waters, with restricted water exchange, for Baltic Sea management is
very important, but not well known. Taking the Oder/Odra estuary as an example
we analyze the long-term pollution history and the major sources for phosphorus
and calculate a phosphorus budget, with special focus on anoxic phosphorus release
from sediments. The budget shows that due to internal eutrophication in July
2000 the lagoon became a major temporary source of phosphorus for the Baltic
Sea. A phosphorus emission reduction scenario, taking into account diffuse and
point sources in the entire Oder/Odra river basin, is presented. Phosphorus load
reductions have only limited effect on the eutrophic state of the lagoon. The lagoon
is more sensitive to nitrogen load reductions. Therefore, both elements have
to be taken into account in measures to reduce eutrophication.
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