Ewolucja systemu hydrograficznego i szaty roślinnej dorzecza górnej Piławy i górnej Drawy (Pomorze Środkowe)

Józef Lewandowski, Małgorzata Nita


Evolution of the hydrographic system and vegetation in the drainage basin of the upper Piława and the upper Drawa Rivers (Middle Pomerania).
A b s t r a c t. Highly varied hydrographic system occurs in the drainage basins of the upper Piława, Płytnica and Drawa Rivers (Middle Pomerania). Numerous radiometric dating carried out by the methods of 14C, OSL and U/Th, as well as pollen analyses and geomorphological analysis enable to study evolution of the system in the period of the last twelve thousand years. Glaciolacustrine deposits, accompanying most of the lakes, represent accumulation, which took place at the initial stage of the lacustrine basin formation. The level of lacustrine waters fell by several to more than a twelve meters in that time and was controlled by melt water runoff channeled through valleys in the southern direction. The final stage of the lake development was connected with complete melting of buried dead-ice masses and formation — bottoms of lake. Evolution from glaciolacustrine to lacustrine basins within kettles was continuous process. Lake water level started to fall abruptly when the last remnants of the dead ice blocking the runoff have melted and the inter-lake channels have been erosionaly deepened. That phase should be related to the complete decay of permafrost, probably at the end of the Allerød. The main phase of erosion in the gorges started at the end of the Pleistocene and lasted (with lower intensity) till the Pre-Boreal and/or the Boreal. The water level in the lake system drained by the Pi³awa and the Drawa Rivers was finally fallen by 8–16 meters and for a long time was stabilized (during the Atlantic and Sub-Atlantic) at the level of 2 meters higher than the present one. Further lowering of drained lakes by the next 2 meters was probably caused by anthropogenic activities resulting from intensive colonization in the 16th and 17th centuries and later by land improvement accomplished in the drainage basins of the Drawa and the Piława Rivers in the 19th century. Local conditions strongly influenced character of forest communities in the area investigated. The tendency was especially significant in the Atlantic. Increased importance of pine trees in the vicinity of the Lędyczek site caused that broadleaf forests with oak, maple, lime and hazel trees, typical of the Atlantic, have not developed there.

Full Text: