Przybałtyckie zbiorniki słonawowodne na tle innych przymorskich wód słonawych

Wiktor, Krystyna

doi:ISSN 0424-7205

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Title: Przybałtyckie zbiorniki słonawowodne na tle innych przymorskich wód słonawych

Abstract:

The south coast of Baltic sea abounds in Coastal bodies of water which constitutea very specific water environment. Apart from three bays: Szczecin Lagoon,Vistula Lagoon, Courland Lagoon we come across a whole series of smalland big lakes covering the surface from some scores of hectares to some scoresof kilometers.The aim of this paper is to bring out their common characteristic featuresand to stress their properties which differenciate them from other brackish watersin the world.Coastal brackish waters of Baltic show many similarities as far as their hydrologicand biologic qualities are concerned, thus using any of the classificationsbased on these premises they fall into the same cathegories. Neither of them fitsinto one class, however, if we take the “Venetian system” of water classificationas a starting point. Apart from the limnetic zone each of them embraces from twoto four zones: from b-mixo-oligohaline to b-or a-mixo- mesohaline. Yet the differencebetween these bodies of water is quite considerable as far as the dynamicsof hydrologic processes is concerned as well as their productivity. This originatesmainly from the difference in the quantity of the river waters supply as comparedto the amount of Baltic waters, the capacity of the body of water etc.It can be stated that the specific stamp of these bodies of water is due to thefollowing factors: a) low salinity of Baltic waters , b) lack of tides in Baltic sea,c) narrow connection of the waters with Baltic sea which makes the exchange ofwaters masses rather difficult, d) climatic factors (the position in the temperatezone).Whereas the first of the factors restricts the number of zones appearing inthe estuaries and provides for the fact that the only species which are to befound among all the sea elements there are euryhaline ones, in a very broadsense of the word, the factors presented in points b, c. d, contribute to the greaterstability of hydrologic conditions of Baltic estuaries in comparison to other brackishestuaries and to the restriction of the zone of greatest changes to a considerably small parts of the body of water.The specific character of Baltic Coastal brackish waters becomes more tangibleagainst the background of other types of brackish waters. Several examplesof brackish waters of other character have been enumerated to point it out: ; 1. Contacting North Sea, tha t is euhaline one, characteristic for great oscillationof the water lev l at the coasts by the tides and situated in the same climaticzone with the Baltic Coastal waters (the brackish waters of the mounth of Elberiver).2. Contacting Mediterranean Sea, the sea of high salinity of waters whichis like Baltic actually deprived of tides and situated in a more dry and warmerclimate (tide waters of the Rhóne river: Camargue, the lakes of de Thau and deBerre), with periodically reduced delivery of river waters.3. Situated in the tropical and subtropical zones with strongly marked seasonalchanges in the supply of fresh waters (river and rainy waters) which contactthe ocean, that is euhaline environment, and are situated in the region where thedifference in the water level connected with tides is great (brackish and mangrove waters of the west coast of Madagascar ).In spite of basic differences between Baltic Coastal brackish waters and otherCoastal waters on Earth which are mainly concerned with hydrologic and productiveprocesses, the degree of stability, the species composition of communities etc. —Baltic Coastal lakes and bays reveal all the features characteristic for Coastalbrackish waters which are the following : a) the lack of stability in hydrologicconditions caused by reversible delta, this being however less prominent thanin some waters of other types, b) the restricted number of species with simultaneous mass development of individuals, c) interrelation between ranges of seaspecies and freshwat r ones, d) great productiyity, particularly that of fish.