Diatom and Cladocera (Crustacea) remains in the sediment of a lowland lake located in an area with a long history of human settlement, covering a period of at least 5,000 yrs, were analyzed and used as proxies to reconstruct past changes in the lake’s trophic state. The changes in trophic state were quantified with the diatom inferred total phosphorus model. The first signs of human impact on the lake’s ecosystem were recorded in the Neolithic (~4,500–4,000 cal. BP) followed by the Bronze ages (3,300–2,800 cal. BP), but they intensified during the Iron age (2,500–1,300 yrs ago) and especially during the Medieval age (after 1,000 yrs ago). Then, the diatom-inferred total phosphorus indicated hypertrophic conditions (DI-TP > 100 µg L-1), and substantial changes in the zooplankton assemblage structure were recorded, namely increase in species related to turbid water and a muddy bottom, pointing toward intensive eutrophication and fishing. The pulses of eutrophication were generally correlated with human settlement phases but inferred increases in the trophic state near 2.8 ka cal. BP and 1.3 ka cal. BP were related to minima of total solar irradiance and were driven by climatic factors and erosion in the lake catchment rather than by human activity. The strongest influence on the lake’s ecosystem was attributed to people of the Bogaczewo culture (dated to the late Iron Age), an early-Medieval Galindia tribe, and economic activity over the last 200 yrs.
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