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Peatlands are important records of past environmental changes. Based on a multiproxy analysis, the main factors influencing the evolution of a peatland can be divided into autogenic and allogenic. Among the important allogenic factors, apart from climate change, are deforestation and drainage, which are directly associated with human impact. Numerous consequences arise from these processes, the most important of which are physical and chemical denudation in the catchment and the related hydrological disturbances in the catchment and peatland. The present study determined how human activities and the past climatic variability mutually influenced the development of a small peatland ecosystem. The main goals of the study were: (1) to trace the local changes of the peatland history over the past 600 years, (2) to investigate their relationship with changes in regional hydroclimate patterns, and (3) to estimate the sensitivity of a small peatland to natural and human impact. Our reconstructions were based on a multiproxy analysis, including the analysis of pollen, macrofossils, Chironomidae, Cladocera, and testate amoebae. Our results showed that, depending on the changes in water level, the history of peatland can be divided into three phases as follows: 1/the phase of stable natural conditions, 2/phase of weak changes, and 3/phase of significant changes in the catchment. Additionally, to better understand the importance of the size of catchment and the size of the depositional basin in the evolution of the studied peatland ecosystem, we compared data from two peatlands – large and small – located close to each other. The results of our study indicated that "size matters," and that larger peatlands are much more resilient and resistant to rapid changes occurring in the direct catchment due to human activities, whereas small peatlands are more sensitive and perfect as archives of environmental changes. [ABSTRACT FROM AUTHOR]

Paleoenvironmental studies previously performed on Lake Igaliku revealed two agropastoral phases in south Greenland: the Norse settlement from AD 986 to ca. AD 1450 and the recent installation of sheep farmers, since the 1920s. To improve the knowledge of the timing and magnitude of the Greenlandic agropastoral activities, a lipid inventory was realized and compared with biological and geochemical data. During the 12th century, a major increase in deoxycholic acid (DOC) and coprophilous fungal spores revealed a maximum of herbivores. Synchronously, a minimum of the n-C29/n-C31 alkane ratio and tree and shrub pollen and a maximum of triterpenyl acetates showed a reduction in the tree and shrub cover, because of grazing activities. Lupanone, produced by angiosperms, appeared simultaneously in the molecular content, probably revealing an introduction of plant species by the Norse, as it has been the case for Rumex spp. No major erosion was recorded by trimethyl-tetrahydrocrysenes (TTHCs) and titanium (Ti) fluxes. No massive algal production, identified by the n-C17/total n-alkane ratio and mesotrophic diatoms, was either revealed. After the Norse abandon (around AD 1450), a return of the vegetation to quasi-pristine conditions was observed in the molecular content. Finally, a re-introduction of sheep in the 1920s provoked major impacts between the 1970s and the 1990s. A major decrease in the n-C29/n-C31 alkane ratio and tree and shrub pollen associated with maxima of triterpenyl acetates, TTHCs, Ti fluxes, and mesotrophic diatoms highlighted a reduction in the tree and shrub cover, a strong soil mobilization, and algal blooms, probably linking to the recent mechanized creation of hay fields and the massive use of fertilizers. In this study, molecular biomarkers revealed two periods of major impacts: the 12th century and between the 1970s and the 1990s, separated by centuries without agropastoral practices, allowing a quasi-resilience of the vegetation. [ABSTRACT FROM AUTHOR]

A multiproxy approach to a sediment sequence at Lake Saint-Point in the French Jura Mountains gives evidence of a strong coupling between changes in terrestrial and lacustrine ecosystems throughout the Holocene. The early Holocene (11,700–10,200 cal. BP) is characterised by the recovery of terrestrial and lake ecosystems favoured by climatic warming. During the middle Holocene (10,600–6200 cal. BP), the climatic optimum coincided with an extension of deciduous forests into the catchment area, while lake sedimentation is dominated by authigenic carbonates and low detrital inputs. After 6200 cal. BP, the Neoglacial favoured expansion of Abies-Fagus forests and increasing detrital inputs to the lake where ostracod fauna declined and changed in composition. After 1200 cal. BP, human impact was responsible for extensive forest clearings in the catchment area, while the lake basin shows contrasting pictures with increasing detrital input, resuming sedimentation of authigenic carbonates and changes in dominant ostracod species. Orbitally driven climatic variations were the dominant factor of environmental changes until c. 1200 cal. BP. Around 2600 cal. BP, human impact increased and became the major factor in the catchment area and the lake basin from 1200 cal. BP onwards. Finally, the Saint-Point record offers a clear illustration of how gradual changes in insolation or increasing human impact may provoke, even under temperate climatic conditions, abrupt responses in mid-European terrestrial and lake ecosystems, and how differences in the dates of tipping points revealed by proxies suggest specific threshold values depending on the sensitivity of indicators used and on their role in the different compartments of these ecosystems. [ABSTRACT FROM AUTHOR]

In order to better understand the evolution of past climate-human-environment interactions in the northwestern Alps during the Holocene, we have analysed the lipid content of two cores taken from the sediments of Lake le Bourget (French Alps). By using a specific molecular biomarker of Panicum miliaceum (broomcorn millet) previously defined and a new molecular marker of soil erosion, we demonstrate that the onset of millet cultivation coincides with the onset of major soil erosion in the catchment during the Middle Bronze Age. Although archaeological and archaeobotanical investigations indicate a discrete human occupation of the lakeshores at this period, they also point to a regional change in agricultural practices that deeply affected soils. The evolution of millet cultivation appears in strong connection with climatic variations, estimated in the same cores from the variations in titanium, a proxy of hydrological changes in the region. Social and cultural triggers cannot be discarded at this stage. Such an approach applied to more sedimentary archives shows high potential to unravel the temporal and spatial dynamics of human land use. [ABSTRACT FROM AUTHOR]