Evolution of sediment composition of the coastal Lake San Puoto (Latium, Italy) in the last two centuries

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Francesca ALVISI *
Enrico DINELLI
(*) Corresponding Author:
Francesca ALVISI | franci@igm.bo.cnr.it

Abstract

The sediment composition of the coastal Lake San Puoto (Central Italy) was studied to obtain information on its recent environmental evolution (last 200 years). The explorative fieldwork was performed within the framework of the EU-funded PALICLAS Project. Sediment and mass accumulation rates, calculated from 210Pb analysis, show mean values of 0.27 cm y-1 and 0.11 g cm-2 y-1 respectively, with increasing values from 10 cm to the top (i.e. from ca 1960 AD to the present). The evolution of the recent sedimentation of Lake San Puoto is characterized by the interplay of three main components: detrital (either siliciclastic and/or carbonatic), organic-rich and authigenic phases. The first reflects the input from coastal dunes and rocky outcrops; the other two indicate variations in lake productivity. Sedimentological, geochemical, and mineralogical analyses of two cores collected near the center of the lake were used to define five lithological units: i) a laminated unit representing the last eutrophication period, starting ca 1925 AD; ii) a few turbidite layers, probably due to a lowering of the lake level around 1920 AD; iii) a productive phase of the lake, which occurred around the end of the XIX and the beginning of the XX century; iv) a coarse siliciclastic sediment interval, possibly deposited following the digging of the channel connecting Lake San Puoto to Lake Lungo; and v) an older unit representing the natural allochthonous detritic sedimentation deriving from the present dune deposits surrounding the lake shores. Metal fluxes were calculated for recent times by means of 210Pb sedimentation rates. Zn, Cu and Pb record considerably higher fluxes above 10 cm depth (i.e. 1960 AD), as confirmed by Al-normalized metal depth profiles. Episodes of eutrophication occurred between 1890 and 1920 and between 1925 and the present.

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