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RELATIONSHIP BETWEEN LANDFORMS AND HEAVY METAL CONTENTS IN THE SOIL OF THE OSTROVSKA LOWLAND ALONG LOWER DANUBE

Velimira Stoyanova, Tsvetan Kotsev

Abstract

This study aimed to reveal the dependence of the spatial distribution of heavy metals in soil on the morphography of the Lower Danube floodplain in the Ostrovska Lowland in Bulgaria. The field campaign was conducted in 2017, and the concentration of Zn, Ni, Pb and Cr were measured in the fine fraction (<0.063 mm) of 10 soil samples using X-ray fluorescence analysis. The average content of Cr in the topsoil (0-20 cm) was 127 mg/kg ranging between 98 – 171 mg/kg. It was followed by Zn – 81 mg/kg (60 – 128 mg/kg), Ni – 54 mg/kg (40 – 85 mg/kg) and Pb – 30 mg/kg (18 – 53mg/kg). The metal levels exceeded the mean values for floodplain sediment in Europe in most samples. Chromium violated the quality target threshold for sediment applied by the Joint Danube Surveys in 90% of the samples and Ni in 60%. The concentrations of all the heavy metals except for Cr showed a relationship with the geomorphographic units. The elements Zn, Pb and Ni tended to accumulate mostly in the marshes and less in the active floodplain and sandy ridges. A negative correlation between vertical distance to the Danube and the concentration of elements was found for Zn (R2 0.73), Pb (R2 0.66) and Ni (R2 0.51). The results confirmed the more intensive accumulation of the three metals in the lowest parts of the floodplain, where the fine sediment was deposited during floods. The individual pattern of the spatial distribution of Cr indicated a specific source of origin of the element. The landforms had little control over the dispersal of the element in the floodplain of the Lower Danube. The obtained results showed that marshes were most threatened by metal contamination if flooded, and this should be consi dered if restoration of wetlands is conducted in the lowland. In contrast, the sandy ridges and high floodplain were naturally protected against the accumulation of hazardous substances via inundation by the Danube.

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DOI resolver: doi.org/10.5593/sgem2021/5.1/s20.051

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