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National park "Mljet" is situated on the island of Mljet in Croatian south Adriatic. Saline lakes of Mljet are National park's phenomenon. Lakes consist of the lake "Veliko jezero" covering an area of 1.45 km2, with a maximum depth of 46 m, while lake "Malo jezero" has an area of 0.24 km2 and a maximum depth of 29 m indicating their isolated character and reduced mixing with the open seawater. These saline lakes are semi-enclosed, relatively deep depressions connected with the open sea by the narrow, shallow Soline Channel. Lakes originated approximately 10, 000 years ago and, until the 4, 000 year, they were freshwater lakes. The depressions in which the marine lakes are located are typically karstic dolinas developed in Mesozoic limestones and dolomites. The formation of these deep dolinas occurred while their bottom was above sea level. It was possible that "Malo jezero" Lake was filled up later than Veliko jezero Lake, some 2, 000 years ago. Literature shows that the sediments from Mljet lakes are investigated in sense of the palaeoecology and palaeoclimatology, but without trace metals concentrations data. Also, precipitation of aragonite in the Mljet Lakes was described. Protected natural areas, particularly National parks, are very sensitive systems because of their substantial uniqueness which should be preserved in their original form. It is very important to assess actual ecotoxic metals concentration levels. Systematic survey (periodic, field/laboratory) is necessary to distinguish elevated trace metals concentrations naturally present in aquatic environment from the anthropogenic influence. Spatial and temporal distribution of five ecotoxic metals (Hg, Cd, Pb, Zn, Cu) in sediments of Mljet National park collected from 2005 to 2008 was studied. Cd, Pb, Zn and Cu concentration measurements were performed by differential pulse anodic stripping voltammetry (DPASV), while mercury investigations by cold vapour atomic absorption spectrometry (CVAAS) were obtained. Results show behaviour of investigated metals particularly in sediments of "Veliko jezero" and "Malo jezero" saline lakes, the two main water bodies in NP "Mljet". Also, results provide evidence of increasing anthropogenic influence during the last few decades in front of Babine Kue village (Veliko jezero), as well as rate of sedimentation, which will be discussed in details. |
