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A paleoecological study (macrofossils, pollen, cryptogam spores, non-pollen palynomorphs) was performed to investigate environmental changes recorded on the peat deposits of the La Narce du Béage mire (Massif Central, France). We reconstructed the development of a limnogenous mire ecosystem during the Holocene, consequently to the infilling of a small Late Glacial lake. Successions from aquatic flora ( Isoëtes, Nitella opaca/ syncarpa, Botryococcus, Alisma plantago-aquatica, Potamogeton, Sparganium) to mire plant species ( Alnus glutinosa, Betula nana, Betula pubescens, Cyperaceae, Ericaceae, Sphagnum) underlined a gradual eutrophication and acidification during the lowering of the water table. We demonstrated a clear link between these local hydro-ecological changes and the early Holocene climatic warming. Also dealing with archeology, we provided key issues for the identification of human-induced environmental changes. Three phases of ecological disturbances with clearings of the mixed-oak forest and agro-pastoral activities were evidenced at 7700–7300, 6800–6420, and 5500–4250 cal. BP. Our results confirmed early Neolithic (Cardial influences), middle Neolithic (Chassean), and late Neolithic (Ferrières group) frequentations of the Béage Plateau, probably included in large-scale socio-cultural changes (SE France, NW Mediterranean Basin). Later, forest clearings (beech and fir), cultivation, and pastoralism were outlined since the Iron Age (after 2300 cal. BP, that is, 350 BC). Increasing human pressure was especially recorded during the last 1700 years, with rye ( Secale cereale) cultivation and extensive livestock grazing around and on the mire, which is nowadays a protected ‘Natura 2000’ area.

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Abstract. Environmental pollution by polychlorinated biphenyls (PCBs) is a key cause for concern about river quality because of their low degradation rates leading to their accumulation in sediments and living organisms. An original interdisciplinary work was conducted along the four main French rivers (Seine, Rhône, Loire and Garonne rivers), which flow into major European seas. We completed a dataset based on sediment analyses provided by monitoring agencies, port authorities and research teams on different solid matrices (sediment cores, bed and flood deposits, suspended particulate matter and dredged sediments). This dataset focused on the seven indicator PCBs and their sum (ΣPCBi) from 1945 to 2018 (nΣPCBi =1416). Special effort was put into the quality control to provide robust spatio-temporal information. Taking into account hydrological and human drivers, we outlined two main pollution trends: (1) from 1945 to 1975, a quick increase in ΣPCBi (up to 4 mg kg−1 dry weight, dw) and a sharp decrease in the 1980s on the Seine and Loire rivers and (2) increasing but moderate ΣPCBi levels (50 to 150 µg kg−1 dw) followed by a decline after the 1990s on the Rhône and Garonne rivers. In addition to these patterns, PCB emissions from urban and industrial areas or accidental events were significant in each river. Finally, when calculating specific flux, the Rhône exhibited the uppermost ΣPCBi load (up to 12 µgm-2yr-1 in 1977–1987), at least 25 % higher than those of the Seine and Loire rivers, while the Garonne showed a very low flux. In western Europe, we confirmed that the Rhône, Seine and Loire rivers contribute significantly to the PCB contamination of the seas, while French specific ΣPCBi fluxes are 2 orders of magnitude lower than those found in American or Asian rivers. The dataset is available at https://doi.org/10.1594/PANGAEA.904277 (Dendievel et al., 2019).

Abstract. Environmental pollution by Polychlorinated Biphenyls (PCBs) is a key concern about river quality because of their low degradation rates leading to their accumulation in sediments or living organisms. This original interdisciplinary work was conducted at a large scale along the four main French rivers (Seine, Rhône, Loire and Garonne Rivers), which flow into major European seas. We completed a dataset based on sediment analyses provided by monitoring agencies, port authorities and research teams on different solid matrices (cores, bed and flood sediments, suspended particulate matters, dredged sediments). This dataset (n=1416) focused on the seven indicator PCBs and their sum (∑PCBi) from 1945 to 2018. Special effort was put on the quality control to provide robust spatio-temporal information. Taking into account hydrological and human drivers, we outlined two main pollution trends: (1) from 1945 to 1975, a quick increase of ∑PCBi (up to 4 mg.kg−1 dry weight, dw) and a sharp decrease in the 1980s on the Seine and Loire Rivers; (2) increasing but moderate ∑PCBi levels (50 to 150 µg.kg−1 dw) followed by a decline after the 1990s on the Rhône and Garonne Rivers. In addition to these patterns, PCBs emissions from urban and industrial areas or accidental events were significant on each river. Finally, when calculating specific fluxes, the Rhône River exhibited the biggest ∑PCBi load (up to 12 µg.m−2.year−1 in 1977–1987), at least 25 % higher than those of the Seine and Loire Rivers, while the Garonne River showed very low fluxes. French specific ∑PCBi fluxes are two orders of magnitude lower than those found in American or Asian Rivers. In Europe, we confirmed that the Rhone and Seine Rivers provide a major supply of PCBi to the Western Mediterranean and the English Channel, respectively. The dataset is available at https://doi.pangaea.de/10.1594/PANGAEA.904277.

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