Late Pleistocene and Holocene environmental evolution of the Wkra River Valley near Bielawy Gotuskie (central Poland) recorded in palaeo-oxbow lake deposits

摘要

This study aimed to reconstruct environmental changes in the Wkra River Valley near Bielawy Gotuskie (central Poland) based on geochemical, palynological and subfossil Cladocera analysis of deposits filling a palaeo-oxbow lake. Two sediment boreholes collected from the palaeochannel bend (BG-1) and neck (BG-2) include full sequences of organic deposits lying on clastic deposits. The lower part of the BG-1 borehole contains gyttja that accumulated during the Younger Dryas and the Preboreal, which is covered by reed peat of Preboreal and Boreal age. On top of this is alder peat that accumulated during the Atlantic. The ages of the gyttja and peat were confirmed by both radiocarbon dating and palynological analysis. The peats are characterized by a significant content of organic matter, which is relatively stable over time. This indicates a low intensity of mechanical denudation in the catchment, which is supported by low concentrations of aluminum and potassium. Calcium values greatly exceed these elements, suggesting that the lake was mainly fed by groundwater. Variation in trophic conditions over time is indicated by a vertical variability in the content of nitrogen, as well as by the Cladocera population. The strong decomposition of peat in the top layer of the mire, and increased concentrations of phosphorus and heavy metals, testify to increasing human activity during the most recent time periods.