Physiographic factors affecting the stratigraphy of peat deposits in the Lower Basin of the Biebrza River / Czynniki fizjograficzne wpływające na stratygrafię złoża torfu w Dolnym Basenie Doliny Biebrzy

Analyses of water conditions in the Lower Basin of the Biebrza River and deposit stratigraphy were conducted in cross-sections through the valley, where geodetic measurements were also made. Peat type in particular layers of the soil profile was determined in selected cross-sections at 100 m intervals. The Lower Basin of the Biebrza River is diverse with regard to the type of water supply to a peatbog, the shape of the bio-accumulative basin’s bottom and the slope of peatbog surface along and across the valley. These factors resulted in the development of different habitats in the peatbog. Northern part of the Lower Basin, between the main road in the village Osowiec and the inflows of the Kosódka and Wissa rivers to the Biebrza River, is a narrow valley supplied mainly with overflowing water of the Biebrza River. Habitats and hydrogenic deposits of this area developed in relation to the type and layout of mineral substratum and to the duration and depth of seasonal flooding. North-west part is mainly supplied by ground water from the adjacent upland. Peat layers, developed on ground waters flowing out from the upland, markedly slope toward the bed of the Biebrza River. Considerable fluctuations of the ground water level can be observed there and most frequently the sites are periodically drying. Part of the valley, from the inflows of the Kosódka and Wissa rivers down to the Biebrza and Narew River confluence, is mainly supplied with underground waters from upland.