Ecological risk assessment and spatial distribution of heavy metals in surface sediments. A case study of two small storage reservoirs, SE Poland

The article shows the results of research on heavy metals (Cr, Zn, Ni, Cu, Pb, Cd) content in bottom sediments of two small storage reservoirs located in the south-eastern part of Poland. The analyses covered the top 10 cm layer of sediment samples taken in transects perpendicular to the shoreline, located in upper, central and lower sections of the studied reservoirs. The ordinary kriging method was applied to interpolate spatial distribution of heavy metals content in the sediments. The assessment of surface sediment contamination with heavy metals was based on a threshold effect level and probable effect level methods. In addition, the ecological risk was assessed on the basis of the indices: potential ecological risk index and toxic risk index. Moreover, the principal component analysis was carried out to find determinants for the distribution of the analyzed trace elements in reservoirs. The results of the completed analysis have proven that the highest concentrations of heavy metals (HM) are found in the vicinity of dams in both reservoirs. Calculated probable effects level values indicate a negative impact of Pb- Blizyn Reservoir (BR) and Cd- Maloszowka Reservoir (MR) on aquatic biota. The analysis of heavy metal content and their interrelationships in surface sediments proves that Pb, Cu and Zn in the BR and Cd and Cr in the MR have anthropogenic origins. Moreover, the main determinants for HM distribution in the reservoir are hydromorphological parameters, which determine sediment grading and organic matter transport.