Tracking long-term human impacts on landscape, vegetal biodiversity and water quality in the Lake Aydat catchment (Auvergne, France) using pollen, non-pollen palynomorphs and diatom assemblages

•Past human-induced environmental disturbances are studied in the Lake Aydat area.•Human actions shaped the cultural landscape and increased the floristic diversity.•1500 years of human impact drove Lake Aydat trophic states towards meso-eutrophy.•1500 years of diversified human actions explain a loss of resilience of the lake.•Rotifer resting eggs are assessed as indicator of lacustrine past trophic states.

Palaeoenvironmental studies allow the assessment of long-term human-climate-environmental interactions, and furnish valuable tools for the sustainable management of lacustrine ecosystems. A good example is the multi-proxy study of Lake Aydat's 19 m sedimentary core. Previous research revealed the role of climate and human activities on lake sedimentation, and identified two sedimentary units (6700 ± 200 to 3180 ± 90 and 1770 ± 60 cal. yr BP to present) separated by an erosive mass-wasting deposit (Lavrieux et al., 2013a). Pollen, non-pollen palynomorphs (e.g. fungal and algal spores, rotifer resting eggs), and diatom-based trophic reconstructions have been used to track the impacts of past land use on landscape evolution, vegetal biodiversity and water quality. Palaeoenvironmental data were also compared with local archaeo-historical datasets which allowed refined landscape reconstructions, especially for late Antiquity. The results obtained demonstrate that even Neolithic and Bronze Age human activities (between ca. 4600 and 4300 cal. yr BP and between ca. 3900 and 3500 cal. yr BP) had a discernible influence on catchment vegetation and lacustrine trophic dynamics of Lake Aydat, underlining the vulnerability of the ecosystem. Recurrent and complex models of past vegetation changes, phases of water nutrient over-enrichment and lake resilience were identified and related to grazing activities, but also to land use practises, which have been overlooked in Auvergne, such as mountain agriculture and hemp retting.