engleski

Changes in lake level and trophy at Lake Vrana, a large karstic lake on the Island of Cres (Croatia), with respect to paleoclimate and anthropogenic impacts during the last approx. 16, 000 years

A multi-proxy approach study ( cladocerans, diatoms, geochemistry, plant macrofossils, pollen), was performed on a sediment core from Lake Vrana (Vransko Jezero) , a large and deep karstic lake on the northern Adriatic island of Cres, Croatia. Considerable lake-level changes occurred during the last approx. 16, 000 years. The stratigraphic evidence suggests that periods of enhanced precipitation and the post-LGM rise in sea level were the main driving forces. The The lake records indicate early human impacts. Sediment echo-sounding indicated that >25m of lake sediments lies within the site, from which 5 m have been cored. Shallow lake stages occured from 14.4 14C ky BP to early Holocene. Prior to Allerod, interglacial sediments were redeposited, reflecting the influences of rising sea-level (forming a local groundwater barrier), a temporary increase in precipitation, and lake-level changes. There appears to be a hiatus in the sequence, for no sediments assignable to the Allerod chronozone could be found. A disordance in the echo profile at the appropoate horizon in the sequence supports this interpretation. Groundwater level increased again at 10.6 ky BP (during Younger Dryas chronozone), a swamp vegetation formed, wehich gave way to a shallow lake. During the Preboreal chronozone), this freswater lake persisted with fluctuating levels. The establishment and subsequent persistence of thepresent deep water lake at about 8.5 ky BP, correspond with findings of pluvial period at the Dalmatian coast, which lasted from 8.4 to 6 ky BP. First human catchment disturbances were related to settlements of Neolithic or Bronze Age. The increase in summer drought, coupled with forest clearance during Illyrian times, are assumed to be responsible for the change towards present evergreen oak vegetation in the lake catchment. The intensification in land-use during Roman and post-Roman settlements caused a slight increase in the lake trophic level.

lake level variations; Late Pleistocene to Holocene stratigraphy; palaeolimnology; palaeoclimate; antropogenic pacts

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