Combining multi-variate palaeoecological indicators and mining closed gradual patterns for refining past lake dynamics and the induced ecological legacies

International audienceThe overloading of water bodies with nutrients is a widespread ecological alteration. Arecent synthesis (CNRS, IFREMER, INRA, IRSTEA) shows that lake ecosystems are partic-ularly concerned by the eutrophication process which results in: (1) ecological disturbances(e.g. invasive species, loss of biodiversity, algal and cyanobacterial blooms), and (2) pub-lic health problems (e.g. water quality degradation due to cyanotoxin production). Thismakes the restoration of eutrophic freshwaters an environmental top-priority and a key-issuefor scientic research. Accurate assessments of the present-day lake ecosystems state arethus needed. Moreover, long-term retrospective models of lake dynamics must be developedconcomitantly to the analysis of natural and anthropogenic modications of the catchment,which enhance the external input of sediment and nutrients. Palaeoecological researches aretherefore required because they characterize through time the lake’s responses to cumula-tive changes caused by natural (e.g. climate) and anthropogenic impacts (e.g. vegetationclearance, agriculture). They furnish thus fresh insights into a good understanding of theecological legacies which also determine current lake structure and function, and which mustbe considered for sustainable lake management. A palaeoecological research was conductedin the hyper-eutrophic Lake Aydat (837 m a.s.l.), located in the Chaˆıne des Puys (FrenchMassif Central). The high resolution and multi-proxy analysis (pollen, non-pollen paly-nomophs, diatoms, sedimentology) was combined to an approach of data mining (extractionof frequent (closed) gradual patterns of multi-variate indicators under temporal constraint)and allow to address the:(1) reference conditions of the lake (prior to extensive human impact) and its natural vari-ability;(2) aquatic changes phases: timing, intensity, frequency, delay;(3) reversibility or directions in which the lake is driven by the long-term cumulative impact(e.g. loss of resilience, ratchet effect);(4) potential drivers: climatevsthe diverse range of land uses;(5) degree of resistance/sensitivity and vulnerability of present-day lake ecosytems