The record of hydroclimatic changes in the sediments of a kettle-hole in a young glacial landscape (north-central Poland)

Multidisciplinary research on the bottom sediments of a kettle-hole at the Retno site (the Brodnica Lake District, north-central Poland) provided some information about changes in hydroclimatic conditions in the Late Glacial and the Holocene. Detailed analysis (sedimentological, palynological, macroremains, geochemical and radiocarbon dating) helped to identify 6 stages in the development of the depression in the village of Gaj (near Retno Lake) with 11 phases of hydroclimatic conditions. Sediments of the Retno profile with a total thickness of 6.72 m reflected individual, natural stages in the development of the depression from a lake to a peat bog. Most of the environmental changes were gradual. A sequence of Late Glacial and early Holocene lacustrine sediments (mainly gyttja) occurred in the floor of the profile. The upper 4.10 m consisted of paludal deposits (peat of transitional and raised bogs) divided at a depth of 1.56-1.54 m b.g.l. by a thin layer of clay dated late Subboreal/early Subatlantic. The presence of this layer indicates a sudden change in the environmental conditions associated with a water level rise. At that time, denudation processes started within the drainage basin, probably induced by human activity. The important effects related to contemporary anthropopressure included desiccation of the peat bog (muck formation in the uppermost 10 cm layer) and elevated trophic conditions resulting in a change of the vegetation cover.