Human impacts and eutrophication patterns during the past similar to 200 years at Lago Grande di Avigliana (N. Italy)

• A short sediment core from Lago Grande di Avigliana (Piedmont, Italy), the second most eutrophied lake in Italy, was analysed for pollen and diatoms to reconstruct land-use changes and to estimate baseline conditions for total phosphorus (TP) in the water column. Varve counts on sediment thin-sections and (210)Pb, (226)Ra, and (137)Cs dating provided a reliable chronology for the past similar to 200 years. The main pollen-inferred land-use changes showed a sharp decrease of hemp retting around AD 1900, as well as a gradual change to less intensive agriculture and increasing abundance of exotic plants since AD similar to 1970. Diatom-inferred TP reconstructions indicated stable TP concentrations until AD similar to 1950, revealing baseline mesotrophic conditions (TP < 25 mu g l(-1)). After AD similar to 1950, TP values increased distinctly and continuously, culminating in the late 1960s with concentrations of 150 mu g l(-1). Subsequently, diatoms implied a linear decrease of TP, with an inferred value of 40 mu g l(-1) in the surface sediment sample. Comparison with instrumental TP measurements from the water column since AD 1980 showed a rapid recovery and allowed a direct validation of the diatom TP inference. However, although the TP concentration has decreased considerably, baseline conditions have not yet been reached. When compared to the limnological effects of sewage discharges on inferred-TP concentration, our results indicated that agricultural land use played a minor role in the lake's eutrophication.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

land-use changes

varves

eutrophication

pollen analysis

diatom analysis

validation

Italy

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