River-lake system as mosaic pattern of landscape patches and their transition zones (ecotones)

A river-lake system (i.e. a river flowing through the lakes) can be perceived as a system of lentic (lake) and lotic (river sections) landscape "patches" and the transitory zones between them. In this system transport and exchange of matter and biological information take place. Taking the Krutynia river (Masurian Lakeland, Poland) and its lakes as an example, transport of different biologically active compounds (like phosphorus) and non-active substances (like chlorides) was characterized. Phosphorus retention was estimated in successive "patches" of the system. The biotic structure and function of the river-lake-river transitory zones were described. They are the places where the particles selection and sedimentation of matter transported in the system take place as well as they are the sites where the selection and exchange of planktonic organisms of different size and reproduction strategy occur.