Vertical and Horizontal Changeability of Chemical Features of Bottom Sediment in River and Lacustrine Sections in Lake-River System

Abstract

Bottom sediment is regarded as an important element in water ecosystem, playing the role of a nutrient “trap” but also of the potential and practically inexhaustible source of nutrients. A various transformations of mineral and organic components (diagenesis, dehydration, recrystallization, cementation, chemical reactions) take place in sediment, leading to the migration of nutrients compounds from sediment to water. The bottom sediment is composed of mineral and organic substances removed from the water during the processes of precipitation, sorption and sedimentation. Bottom sediment, that fills river beds, is characterized by a completely different chemical composition comparing to lake sediment. This is caused by the constant flow of water in the river and its good oxygenation. The aim of study was analysis of chemical composition of riverine and lacustrine bottom sediment. Research of bottom sediment was carried in the lake - river system of upper Paslçka. The upper Paslçka basin is situated in the north-east of Poland. The river Paslçka flows into Vistula Lagoon. The total area of the upper Paslçka River basin is 246.7 km2, while the length of the upper part of the river is 40.5 km (total area of Paslçka catchment is 2294.5 km2, total length of river is 211 km). The average fall of the upper course of Paslçka is 1.70 %o. Paslçka River in upper course flows through the lakes with different morphometric properties: Paslçk, Wymój, Sarçg, Lçguty and Is^g. The surface of lakes ranges from 8.5 to 397.5 ha, and a maximum depth - 5.0 to 54.5 m. The research showed a clear spatial differentiation of the content of silica, organic matter and carbon dioxide in the bottom sediments of particular river and lakes sections. The percentage share of other bottom sediments components i.e. macroelements (Ca, Mg, Fe, Mn) and nutrients (P, N), was also various in river and lake sediment. The dominant component of river sediments was silica (56.9 to 96.7% d.w.). With the flow of the river, the share of silica in the sediment was higher. In lake sediment, silica was also predominant, but not in such a wide range as in the river (24.8 to 53.2% d.w.). The content of organic matter in river sediment did not exceed 27%. In the sediments of the lakes Paslçk and Sarçg organic matter was the second component of sediments and ranged from 19.5 to 30.1%. In other lakes the content of organic components ranged from 12.3 to 20.3%. In lake sediment a high proportion of carbon dioxide was noted - between 14.4 and 24.2%, while in river sediment, this component did not exceed 6.3%.