Uwarunkowania geomorfologiczne migracji metali ciężkich w osadach fluwialnych: dolina Małej Panwi

Abstract

Geomorphological influences on heavy metal migration in fluvial deposits: the Ma³a Panew River valley (southern Poland).S u m m a r y. Heavy metal concentrations were investigated in the overbank and channel sediments of the Mała Panew River in southern Poland. Overbank sediment samples were taken in ten vertical profiles up to 2.2 m long within paleochannel infills in four selected XX century floodplains and in 66 profiles,60 cm-long, situated at different height above the water table. Channel sediments were sampled 12 times at the same 10 channel locations within the period of two years. In samples collected, Ba, Cd, Cu, Pb, and Zn concentrations were determined and for selected samples sequential extraction was carried out.Within incised and laterally stable river sections polluted, 20th century sediments occur only in a narrow terrace steps up to 2 m high. Also, in the regulated river section, polluted sediments occur only in several cm thick layers on the 1.8–2.2 m high flood plain. On the contrary, in natural forested valley sections, in which river channel migrates laterally 0.5 m/year on average, the thick polluted sediments occur along the channel at depth up to 2.5 m in a zone about 50 m wide. Differences of heavy metal concentrations between sediment layers of similar age, high proportion of Cd and Zn in the mobile exchangeable fraction and poor buffer capacity of sandy sediments suggest rather high migration rate of Cd and Zn and much lower of Ba, Pb and Cu. Also very high Cd and Zn concentrations in sandy channel sediments could be related to transportof these elements in solution and precipitation. The migration of metals depends most of all on frequency of groundwater level fluctuations. The intensive river bank erosion and clear evidences of metal migration in natural river reaches suggest rapid transfer of these elements between the channel and river banks. Along river reaches with the stable river channel, the floodplain represents a long-term sink for heavy metals and their transfer back to the channel is much slower. The incised river reaches, in which the smallest amount of the heavy metal polluted sediments accumulates are transitional zones for heavy metal load.