Fourteen years of palaeolimnological research of a past industrial polluted lake (L. Orta, Northern Italy): An overview.

The first sediment core analyses were carried out in 1958, but it is only from 1985 onward that a modern palaeolimnological approach was applied to the study of Lake Orta, a large and deep lake in North Italy, heavily polluted by ammonia and copper for about 50 and 30 years, respectively. Thus, we summarise those studies from a variety of sediment cores, collected in different years and sites, using both published and unpublished data. Changes in algal pigments (mainly chlorophyll derivatives, total and single carotenoids), inorganic geochemistry, especially heavy metals (e.g. Cu), diatoms, Cladocera, and thecamoebians were studied and related to the stressed environment. The whole picture reveals a close relationship between modifications in algal biomass, density, taxonomic composition and organisms size on the one hand, and water chemistry changes on the other hand. Long-term history of this lake over 7-8 centuries, including invertebrate and terrestrial vegetation dynamics (pollen stratigraphy), reveals close relationship with natural (climate) and anthropogenic forces.