Late Glacial and Early Holocene lake level fluctuations in NE Poland tracked by macro-fossil, pollen and diatom records

Late Glacial and Early Holocene vegetation history and lake level fluctuations in NE Poland were described based on high-resolution plant macrofossils analyses and records of pollen, diatoms, and radiocarbon dates. The development of Lake Kojle-Perty began in the Allerød (GI-1c). Cooling during the Younger Dryas (GS-1) led to the development of communities of heliophyte herbaceous plants. Palaeobotanical and lithostratigraphical records demonstrate that abrupt climate changes at approximately 11,600 and 9450 cal. BP resulted in distinct changes in the vegetation and water level of Lake Kojle-Perty. Climate warming in the Younger Dryas-Holocene transition (11,600 cal. BP) caused the development of the terrestrial vegetation dominated by cold deciduous forest (Betula), and appearance of thermophylious aquatic plants: Typha latifolia, Najas marina, and Ceratophyllum demersum. A gradual decrease in the lake level since 11,200 cal. BP is evident from the appearance of plants from shallow lake environments (Potamogeton natans and Hippuris vulgaris). The low water levels since 10,700 cal. BP resulting from increased temperature and evaporation caused the development of peat on limnic sediments. The dry and warm climatic phase with lowest lake level in the lakes of NE Poland were coeval with the expansion of temperate deciduous forests (Corylus and Ulmus) that commenced at approximately 10,500 cal. BP. A distinctive increase in lake levels at approximately 9450 cal. BP is suggested by the development of rush plants such as Cladium mariscus and aquatic plants such as Najas marina, Chara sp., and Nuphar lutea in the shallow parts of Lake Kojle-Perty. The increased lake levels correspond with the expansion of Alnus glutinosa in North-East (NE) Poland. Our reconstructions of the vegetation development and lake level changes align with results from other studies in the region.