Pollution and Potential Ecological Risk Evaluation of Heavy Metals in the Bottom Sediments: A Case Study of Eutrophic Bukwałd Lake Located in an Agricultural Catchment

Metals are natural components of the earth’s crust and are essential elements in the metabolism of fauna and flora. However, some metals at high concentrations may pose an ecological risk. Ecological risk analysis is one of the best methods for detecting potential metal pollution problems and its impact on ecosystems. This study analyzed the potential ecological risk and contamination from heavy metals (Cd, Cu, Pb, Ni, Cr, and Zn) in bottom sediments. It analyzed the spatial variability of heavy metal concentrations in the bottom sediments of Lake Bukwałd. The potential ecological risk index (RI) was used to assess the impact of pollutants accumulated in bottom sediments on the environment. In addition to RI, the geochemical index (Igeo) and contamination factor (CF) were also calculated. The pollutant loading index (PLI) was used to compare the average content of metals in the bottom sediments of lakes. The obtained results indicate that agricultural activity determined the quality of the bottom sediments of the reservoir and the spatial content of trace metals in them. Higher concentrations of elements were found in sediments collected from the agricultural catchment, whereas the lowest concentrations were observed near the outflow from the lake. The calculated RI value was 153.3, representing a moderate ecological threat risk. The concentration of cadmium had the greatest influence on the value of the indicator. The analysis of the scale of pollution of bottom sediments using the geochemical index showed that the bottom sediments in terms of the content of most of the trace metals tested are class II. In Cu and Zn, the Igeo index classified these deposits as class 0 and class I. The highest CF values were determined for Cr, Ni, and Pb and classified as significant contamination. The remaining elements were classified as moderately contaminated. The designated PLI was 2.49, suggesting immediate action to reduce pollution and prevent the degradation of the lake.