Biogeochemistry and sedimentology of Lago di Lesina (Italy).

The Lago di Lesina (Lesina Lake, southeastern Italy) is a coastal pond located on an alluvial plain to the north of Gargano Promontory. The aim of this work was to study the depositional and hydrological processes, the benthic environment and the heavy metal sediments pollution of Lesina Lake. The study was carried out by Redox potential, water content, grain-size, mineralogical and biogeochemical analyses in surface sediments collected from 100 sampling stations in the coastal pond bottom. The results showed a predominance of three types of bottom pelitic sediments of different origins and compositions: siliciclastic, carbonatic, and organic. Siliciclastic sediments, which were found especially in the western basin and in the northwestern sector of the central basin, are due to inputs from Acquarotta Canal, some intermittent western streams, and deflation by northerly winds of the sandy barrier that separates the lake from the sea. Carbonate sediments are carried by streams and canals draining the carbonate rocks of the Gargano Mountains and entering the lake from its eastern and southeastern border, these sediments are predominant in the eastern basin and in the southeastern sector of the central basin. Organic matter is abundant throughout the whole lake; it is due to the high productivity of the Lago di Lesina waters that are rich of nutrients for inputs of waters draining the surrounding intensively cultivated agricultural areas. The finer bottom sediments of the lake tend to be removed from the shallower bottoms between the central and eastern sub-basins and near the borders to be deposited in the central portion of the central and western sub-basins. Heavy metal sediment pollution due to anthropic inputs is limited and consists of As, Pb, Cu, and Ni in the western basin, Cu, Zn, and Ni in the eastern basin, and Pb along the northern border.