Typologie des Brackwassers

Abstract

The Venice System for classification of brackish waters is based on one single factor, salinity, and consequently is not fit for a biological classification. I have amended the system by defining the different subdivisions according to their biological features (den Hartog 1960). It appears that the transition area between fresh and sea water usually shows a tripartition. In the different types of brackish water this tripartition is caused by different factors connected with salinity. In the estuaries the enormous daily salinity fluctuations exercise a too great pressure on the osmotic capacity of many species and thus form an effective barrier for them. In the Baltic Sea, where the salinity conditions are more or less stable, the salinity limit for many species is also the limit of their salinity tolerance. In lagoons and isolated brackish waters the minimum and maximum salinities are decisive for the absence or presence of several species. Although in all these waters the subdivision in an oligohaline, a mesohaline and a polyhaline subtype is evident, there is no reason to suppose that the ranges of the corresponding subtypes will coincide, the more so as their boundaries are determined by different environmental factors. In this paper, therefore, a typological system for the brackish waters is proposed, based on the continuity or discontinuity of the transition between fresh and sea water, and on the periodicity of the salinity fluctuations. In some of the eight recognized types a subdivision according to the amended Venice System is possible. © 1964 Biologischen Anstalt Helgoland.