Assessment of nutrients and heavy metals in the surface sediments of the artificially lake water reservoir Karla, Thessaly, Greece

In this research, the sediment quality of the recently reconstructed Lake Karla (central Greece) was evaluated by monitoring the nutrient loadings and heavy metal concentrations in 16 sites during the initial period of the lake’s rehabilitation. The results indicated that lake sediments exhibited a high nutrient status as manifested by the high loadings of organic carbon (OC), total nitrogen (TN) and available phosphorus (AP). Comparison of metal (Ni, Cr, Co, Zn, Cu and Pb) levels with sediment quality guidelines showed that Ni and Cr were found in concentrations well above the PEL (probable effect level) values. No correlations were found between the nutrients and the measured heavy metals. Multivariate analysis results implied that Ni, Cr, Co, Cu and Zn were controlled by natural geological sources whereas Pb might have an anthropogenic origin. The bioavailability ratios of metals followed a decreasing order of Pb > Cu ~ Co > Zn > Ni > Cr based on results obtained by a single 0.5 M HCl leach. Total and bioavailable concentrations of metals demonstrated significant seasonal variations but trends could not be generalized for all the elements. On the contrary, the nutrients did not show significant seasonal differences indicating that the lake sediments record the history of contamination with regard to nutrient status.