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This study investigated the history of the development of six, paleo-lakes, which are at present filled with sediments, in a dune area in Central Poland, based on multiproxy paleoecological analyses and accelerator mass spectrometry radiocarbon dating. The aims of the paleoecological studies were: i) to determine the initial age of lakes development, ii) to reconstruct the local and regional plant succession, as well as iii) to reconstruct the environmental conditions during the initial stage of the development of lakes and peatlands. The obtained results indicated that: the former lakes in dune depressions were developed during the Bølling and Allerød when sparse vegetation allowed strong aeolian activity. Climate warming in Bølling led to the development of a denser plant cover, inhibition of sand transportation and the formation of mid-dune reservoirs with the accumulation of organic sediments. As indicated by 14C dating, mid-dunes basins were formed between 14 686 ± 60 cal. yr BP and 13 421 ± 60 cal. yr BP. The results of the paleobotanical analysis suggested that the reservoirs were shallow, oligo-mesotrophic, inhabited by pioneer calcicole vascular plant species such as: Chara sp., Hippuris vulgaris, Potamogeton natans, Potamogeton fresii, Potamogeton alpinus and Potamogeton filiformis, and mosses such as: Pseudocalliergon trifarium, Calliergon sp. and Calliergonella cordifolium. The area next to the reservoirs was covered with sparse pine forests combined with birch, which is typical of the Late Glacial period. The open areas were dominated by psammophilic and steppe vegetation, including Poaceae, Artemisia and Hippophae rhamnoides. Geochemical analysis revealed that Ca2+ and Fe3+ were in high concentrations, which could have influenced the presence of taxa preferring soil with high Ca2+ content. The accumulation of calcium in sediments confirms that the reservoirs were fed by groundwater originating from the progressive degradation of permafrost associated with thermal changes. [ABSTRACT FROM AUTHOR]

We present results from a palaeoecological analysis conducted on deposits accumulated in an oxbow lake of the Prosna River (Poland), next to the Grodzisko fortified settlement. Palaeobotanical and geochemical analyses—supported by radiocarbon dating—were performed to (i) reconstruct palaeoenvironmental conditions of the oxbow lake and its surrounding area; (ii) determine the beginning of the human activity in the fortified settlement vicinity; and (iii) assess the impact of human pressure on the environment. The Grodzisko fortified settlement was originally located on a river island, encircled by a wetland, improving its defensive value. Increases in the water level (1800–1300 BC and 700–200 BC) created a small lake/moat around the fortified settlement. Indicators for human activity from pollen records suggest the presence of human populations from the late Neolithic, ca. 2800 BC, with a clear intensification ca. 1700 BC. From ca. 1600 BC, a decrease in some decidous trees suggests forest clearance. Low levels of human activity indicator pollen ca. 2000 BC suggest a reduction of human pressure (possible depopulation). The regular presence of macrocharcoal pieces and an increase in human activity indicator pollen from ca. 1300 to 200 BC provide evidence for renewed human habitation around the sampling site. [ABSTRACT FROM AUTHOR]

Sediments from an oxbow lake located in the Prosna River valley (Poland) were analysed to investigate the developmental history of the wetland ecosystem and any response to abrupt climatic changes. High resolution plant macrofossil analysis and radiocarbon dating were undertaken on two cores, with lower resolution geochemical analysis conducted on one of these cores. We provide evidence of a palaeolake with a late Glacial origin (older than 12,500 years). Abundant fossil presence of macrophytes (e.g. multiple Potamogeton species) in the studied palaeomeander may indicate that the north–south orientation of the Prosna valley made it an important route for the spreading of aquatic plants during the late Glacial. Chara sp., Batrachium sp. and Potamogeton spp. were the pioneer plants that colonised cold water with a high Ca2+ content. Early Holocene warming trigged a decrease in water level at the oxbow lake and facilitated the expansion of thermophilous water plants, for example, Ceratophyllum demersum, Typha sp. and Lemna trisulca, which usually occur in shallow water. A decreasing water level resulted in the gradual isolation of the study site from the influence of groundwater, leading to acidification of the habitat and the development of a Sphagnum population, with S. contortum and S. teres as dominant species. The presence of S. contortum (the oldest occurrence in the European lowlands) and S. teres during the early Holocene may indicate that river valleys and the peatlands that developed in this region acted as an important habitats (and possibly refugia) for some minerotrophic Sphagnum species. [ABSTRACT FROM AUTHOR]