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

Heavy metal concentrations were investigated in the overbank sediments in the middle reach of the regulated Odra River, in south-west Poland. Samples of sediments were taken in 20 vertical profiles to a depth of 70 cm at 1–20 cm intervals. Regulation and lateral stability of the river channel for over 150 years enabled to follow the decrease in depth of the Cu and Pb concentration peaks across the floodplain. These peaks were recognised at different depth of the particular profiles: at about 40 cm in the inter-groin infills several meters from a river bank, at 25 cm in the levee at the edge of the floodplain, at several cm in crevasse splays and depressions parallel to flood-protection embankments. These peaks are correlated with maximum Cu and Pb emission and discharge of the mine effluents polluted with heavy metals in the Legnica Copper District at about 1980. Moreover, in profiles localised close to river banks, there are two peaks of Zn concentrations. The upper peak was dated at about 1987 and seems to be associated with the changes in amount of effluents discharged to surface waters in the upper and middle Odra River catchment. The lower one was dated at the first half of the 1940s and can be related to changes in industrial potential and population density after World War II. Dates of sediment layers in different vertical profiles show that the highest rate of sediment accretion, 10–20 mm yr−1, has occurred in the inter-groin infills. Much lower rate, 3–6 mm yr−1, has typified the levee on the 3 m-high floodplain and the lowest one, up to 1–2 mm yr−1, is found in crevasse splays on the flood plain.