No abstract

Human-induced fluctuation of lake levels has been a common phenomenon in Europe since Neolithic times. At present, Lake Tresssee is a eutrophic lake covering less than 5 ha in northern Germany, but its sudden shrinking from ~125 ha before 1800 is considered a consequence of anthropogenic lowering of the lake level. We investigated the history of anthropogenic vegetation changes and water level fluctuations by multiproxy studies of a 4 m core from the former lake area. Our analyses of pollen and Cladocera subfossil, chemistry and sedimentological features yielded important conclusions about interactions between land-use history and climate impacts on the lake and its surroundings. The results indicate that the highest lake level persisted until the Late Atlantic. Since the Subboreal there have been several fluctuations, mostly in consequence of climate impacts. Later, different phases of sediment input to the lake from tributary streams and probably also from aeolian processes from an adjacent dune field were observed. At ~2800 BC the sedimentation rate decreased in consequence of fluvial impacts, as the lake basin was nearly filled up with deposits. As a result of greater human impacts, from the Early Bronze Age the macrophyte zone expanded in the lake, the oxygen content of the water continuously decreased, and heathlands developed in the surroundings. From the Late Iron Age and in the Early Medieval, pollutants probably from ironworks are detectable by geochemical analyses in the corresponding segments. In the pollen diagram the Migration Period is clearly visible, but the suggested radiocarbon date is younger than in Lake Belau in the neighboring region of Schleswig-Holstein. Most probably our pollen diagram did not register the absolute maximum values of Fagus related to the Migration Period. From the Early Medieval a clear phase of resettlement occurs. Since the Early Modern period, the lake level has shrunk rapidly in consequence of historically documented human activity.

No abstract

No abstract

No abstract

No abstract

Fourier Transform Infrared (FT-IR) spectroscopy and imaging combined with hierarchical cluster analysis (HCA) was applied to analyse biochemical properties of Early Middle Ages hemp (Cannabis sativa L.) bast fibres collected from lake bottom sediment of lake Słone. The examined plant macrofossil material constitutes residues of the hemp retting process that took place in the 7–8th century. By comparison of three samples: untreated isolated bast fibres, and fibres incubated overnight at 4 and 37 °C, we were able to mimic the retting conditions. Using FT-IR qualitative and semi-quantitative assessment of the primary polysaccharides content, total protein content, and their spatial distribution was performed within the hemp fibres. The concentration of cellulose remained vastly unchanged, while the concentration of lignin and pectin was the highest in the untreated sample. The spatial distributions of compounds were heterogeneous in the untreated and 4 °C-incubated samples, and homogenous in the specimen processed at 37 °C. Interestingly, a higher amide content was detected in the latter sample indicating the highest degree of enzymatic degradation. In this study, we show that the spectroscopic methods allow for a non-destructive evaluation of biochemical composition of plant fibres without preparation, which can be an appropriate approach for studying ancient plant remains.

Lake sediments not only store the long-term ecological information including pollen and microfossils but are also a source of sedimentary DNA (sedDNA). Here, by the combination of traditional multi-proxy paleolimnological methods with the whole-metagenome shotgun-sequencing of sedDNA we were able to paint a comprehensive picture of the fluctuations in trophy and bacterial diversity and metabolism of a small temperate lake in response to hemp retting, across the past 2000 years. Hemp retting (HR), a key step in hemp fibre production, was historically carried out in freshwater reservoirs and had a negative impact on the lake ecosystems. In Lake Slone, we identified two HR events, during the late stage of the Roman and Early Medieval periods and correlated these to the increased trophy and imbalanced lake microbiome. The metagenomic analyses showed a higher abundance of Chloroflexi, Planctomycetes and Bacteroidetes and a functional shift towards anaerobic metabolism, including degradation of complex biopolymers such as pectin and cellulose, during HR episodes. The lake eutrophication during HR was linked to the allochthonous, rather than autochthonous carbon supply—hemp straws. We also showed that the identification of HR based on the palynological analysis of hemp pollen may be inconclusive and we suggest the employment of the fibre count analysis as an additional and independent proxy.