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Geomorfologiczne uwarunkowania występowania naturalnych barier izolacyjnych w wybranych dolinach rzecznych Niżu Polskiego

Falkowska E.

Przegląd Geologiczny

2002

Vol. 50, nr 10/2

929-936

Geomorphological investigations in the eastern part of the Polish Lowlands have demonstrated the predominance of rivers with an "inherited" character, that is rivers which have adapted a series of depressions after glacial melt-outs for their flow. Initially vast and shallow overflow lakes filled these depressions, in most cases giving parts of valleys, and occasionally also whole valleys a basin shape. The lakes were completely filled with marsh sediments: lake clays, gyttia, organic muds and peats. The admixture of channel sediments in basin-like river valleys is rather small in relation to their area. Due to areal deglaciation typical morphological forms developed in the Polish Lowlands. These include basin-like valley bottoms of lacustrine origin, side valleys connecting postglacial smaller melt-outs on the plateau, glacigenic deformations in the edge zones of the plateau and postglacial accumulation plains with a high-stand or ice-dammed sandy-silty cover. Regularities in the occurrence of features testifying for a glacial origin of wide and long sections were observed in river valleys of Supraśl, Nida, Wkra, Narew, Nurzec, Toczna, Tyśmienica, Piwonia, Krzna, as well as within the neighbouring plateaux. A geomorphological model of large areas was presented, along with the evaluation of the susceptibility of cover soils to pollution. Only such analysis enables an rational economically management of these areas. Lithological characteristics of sediments, filtration coefficient, cation exchange capacity (CEC), heavy metal sorption (Pb, Cd, Cu) and sorption intensity of Pb, Cd and Cu were adopted as indicators of the capacities of sediments building inherited river valleys and adjacent areas to retention of pollution. Sub-surface sediments of the same origin reveal similar physico-chemical properties despite their different age and different range of the particular glaciations, therefore they can be divided into five classes in respect to their capacities to retain pollution. Class I includes sediments with high capacities to retain pollution, i.e., peats, while class V includes sediments with very poor retention capacities, i.e., sands of the channel facies. The evaluation of pollution retention in the case of the investigated polygenic melt-out river valleys and adjacent areas depends on the occurrence of two zones. The first is the valley bottom, a vast area with considerably thick organic sediments (of lake and marsh origin) with high sorption capacities. These sediments create natural isolation barrier. The second zone is the plateau with slope wash sediments and kame terraces and with postglacial accumulation plains. Apart from sediments with very high capacities to retain pollution (clays), sedimentss with much lower capacities such as sands also occur there. The efficiency of the protection cover occurring within bottoms of the studied river valley section depends largely on its continuity, which can be affected by: a) valley kames within peat layers, b) glaciogenic deformations, complicating recharge, c) engineering objects.