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Concept
Lagune de Szczecin
Résumé
Szczecin Lagoon (Zalew Szczeciński, Stettiner Haff), also known as Oder Lagoon (Oderhaff), and Pomeranian Lagoon (Pommersches Haff), is a lagoon in the Oder estuary, shared by Germany and Poland. It is separated from the Pomeranian Bay of the Baltic Sea by the islands of Usedom and Wolin. The lagoon is subdivided into the Kleines Haff (Mały Zalew, "small lagoon") in the West and the Wielki Zalew (Großes Haff, "great lagoon") in the East. An ambiguous historical German name was Frisches Haff, which later exclusively referred to the Vistula Lagoon.
From the South, the lagoon is fed by several arms of the Oder river and smaller rivers like Ziese, Peene, Zarow, Uecker, and Ina. In the North, the lagoon is connected to the Baltic Sea's Bay of Pomerania with the three straits Peenestrom, Świna and Dziwna, which divide the mainland and the islands of Usedom and Wolin.
The lagoon covers an area of 687 km2, its natural depth is an average 3.8 metres, and 8.5 metres at maximum. The depth of shipping channels however can exceed 10.5 metres. Thus, the lagoon holds about 2.58 km3 of water. The annual average water temperature is 11 °C.
94% of the water loads discharged into the lagoon are from the Oder river and its confluences, amounting to an average annual 17 km3 or 540 m3 per second. All other confluences contribute a combined annual 1 km3. Since no reliable data for an inflow from the Baltic Sea exist, the combined inflow is an estimated 18 km3 from a catchment area of 129,000 km2, residing in the lagoon for an average 55 days before being discharged into the Pomeranian Bay. The nutrients thereby transported into the lagoon have made it hyper(eu)trophic to eutrophic. The straits Peenestrom, Świna and Dziwna are responsible for 17%, 69%, and 14% of the discharge, respectively.
The average salinity is between 0.5 and 2 grams of salt per kilogram of water (approximately equivalent to 0.5 and 2 parts per thousand [ppt]). Occasionally northerly winds reverse the direction of the Świna, admitting sea water from the Baltic Sea into the lagoon, raising the local salinity to 6 ppt.
Source officielle
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