Palaeoproductivity and environmental changes during the Holocene in Central Italy as recorded in two Crater lakes (Albano and Nemi)

Three cores from two crater lakes in central Italy (Albano and Nemi) spanning the last ca. II kyr BP age discussed here. They were analysed far organic matter, dry density, algal and photosynthetic bacteria pigments, diatoms and Cladocera. These palaeolimnological records show great internal consistency in their response to distinct, but inter-related, aspects of the lake- catchment system, and reflect major changes in these systems particularly in late productivity. The early Holocene was characterised by very high productivity at both sites. Trends in productivity age similar far many proxies in the Holocene records of Lake Albano and Lake Nemi. Trophic levels throughout much of the period of human activity (ca. 4000 yr BP onward) age lower but have remained relatively high and stable at both lakes. It is only in the last few decades that inferred productivity levels have exceeded those of the early Holocene. Statistical analysis (CONstrained IncrementaI Sum of Square cluster analysis, CONISS) showed five distinct periods during the Holocene characterised by major variations in the abundance and community structure of biological remains and geochemistry. A comparison of results from the different taxonomic groups has enabled the reconstruction of phases of increased productivity and the recognition of signals of anthropogenic impact on the lakes and their catchments. From published pollen diagrams, nine major deforestation events age recognised during the Holocene. These events, in particular the one which occurred in both lakes at .!800Yr BP and identifies the Roman Period, plus another at 3000-3500 yr BP related to agricultural activity during the Bronze Age, produced profound changes in the pelagic community structure of diatoms and Cladocera, which in some cases were even more marked than the accelerated eutrophication seen in recent times. The mid-Holocene climatic transition is also clearly evident and is characterised by a strong decrease in the concentrations of the biological proxies. Most of the observed lacustrine environmental changes age almost synchronous in the two lakes indicating the importance of regional rather than local changes.