Heavy Metals in Vertical Profiles of the Middle Odra River Overbank Sediments: Evidence For Pollution Changes

Heavy metal concentrations were investigatedin the overbank sediments in the middle reach of the regulatedOdra River, in south-west Poland. Samples of sediments weretaken in 20 vertical profiles to a depth of 70 cm at 1–20 cmintervals. Regulation and lateral stability of the riverchannel for over 150 years enabled to follow the decrease indepth of the Cu and Pb concentration peaks across thefloodplain. These peaks were recognised at different depth ofthe particular profiles: at about 40 cm in the inter-groininfills several meters from a river bank, at 25 cm in thelevee at the edge of the floodplain, at several cm in crevassesplays and depressions parallel to flood-protectionembankments. These peaks are correlated with maximum Cu and Pbemission and discharge of the mine effluents polluted withheavy metals in the Legnica Copper District at about 1980.Moreover, in profiles localised close to river banks, thereare two peaks of Zn concentrations. The upper peak was datedat about 1987 and seems to be associated with the changes inamount of effluents discharged to surface waters in the upperand middle Odra River catchment. The lower one was dated atthe first half of the 1940s and can be related to changes inindustrial potential and population density after World WarII. Dates of sediment layers in different vertical profilesshow that the highest rate of sediment accretion, 10–20mm yr^-1, has occurred in the inter-groin infills. Much lowerrate, 3–6 mm yr^-1, has typified the levee on the 3 m-highfloodplain and the lowest one, up to 1–2 mm yr^-1, is found increvasse splays on the flood plain.