engleski

Holocene environmental changes in Baćina lakes

The Baćina lakes are relatively small (total surface is 1.4 km2) freshwater lakes connected to the sea, but are among the most interesting phenomena in karst hydrogeology. The shape of the lakes is irregular, which is reflected also in the lake bottom relief and detailed bathymetry has been done. Important aspect of the lakes is their connection by tunnels (2 km long) with the Vrgoračko polje, for the drainage of excess water from the polje, and with the sea, to prevent flooding and allow agriculture in the catchment. The 8.4 m core from the deepest lake, Lake Crniševo, showed the peaceful environment, not disturbed by the anthropogenic pollution caused by intensive agriculture developed around the lakes after the construction of the tunnel that connects them to the sea, while in the lake where the tunnel is (Podgora), show higher values of Cu and Pb in the upper 30 cm. The age of the core in Crniševo dates back to the beginning of the Holocene (8.3 m is around 11, 700 cal BP). In that period Lake Crniševo existed as shallower lake than today, reflected in the higher concentrations of the lithogenic elements and magnetic susceptibility of the sediment, which indicate increased erosion and input of the siliciclastic material from the catchment from 11.7 to 10 cal ka BP, followed by their gradual decrease until 7.5 cal ka BP. Dominant carbonate deposition lasted from 7.5 until 4.5 cal ka BP. Typical Mediterranean vegetation was determined from the 7.5 cal ka BP. At 4.5 cal ka BP intensive changes in the sediments began, observed by the high sand fraction compared to silt that was dominant until this period. This dynamic environment lasted until 2.5 cal ka BP, and is characterized by alternation of intervals containing calcite and quartz with those in which only calcite is present. From that time (4.5 cal ka BP) the slow increase of the siliciclastic material content were observed, indicating the increasing human impact and deforestation of the catchment. Tephra was identified by the very high magnetic susceptibility and other magnetic properties, so as higher elements K, Na, Mg, Zr in the overall chemical composition of the sediments and it is assumed that tephra belongs to Agnano Astroni Monte Spino (AMST), the eruption of the Phlegraean fields around 4400 cal BP. In Lake Crniševo, the lake sediments show the same signature as the soils in the catchment, hydroxyl interlayered vermiculite (HIV), kaolinite and illite, and lack of association from the sediments in Vrgoračko polje, which can be seen in the upper and bottom sediments from the Lake Podgora. Clay minerals showed influence of the sediments from Vrgoračko polje in Baćina lakes in recent period after the tunnel has been built and in the past.

paleolimnology; geochemistry; polen; ostracods; environmental changes; Holocene; Baćina lakes

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