Holocene lake-level evolution of Lake Tiefer See, NE Germany, caused by climate and land cover changes

Lake-level reconstructions are a key tool in hydro-climate reconstructions, based on the assumption that lake-level changes primarily reflect climatic changes. Although it is known that land cover changes can affect evapotranspiration and groundwater formation, this factor commonly receives little attention in the interpretation of past lake-level changes. To address this issue in more detail, we explore the effects of land cover change on Holocene lake-level fluctuations in Lake Tiefer See in the lowlands of northeastern Germany. We reconstruct lake-level changes based on the analysis of 28 sediment records from different water depths and from the shore. We compare the results with land cover changes inferred from pollen data. We also apply hydrological modelling to quantify effects of land cover change on evapotranspiration and the lake level. Our reconstruction shows an overall lake-level amplitude of about 10 m during the Holocene, with the highest fluctuations during the Early and Late Holocene. Only smaller fluctuations during the Middle Holocene can unambiguously be attributed to climatic fluctuations because the land cover was stable during that period. Fluctuations during the Early and Late Holocene are at least partly related to changes in natural and anthropogenic land cover. For several intervals the reconstructed lake-level changes agree well with variations in modelled groundwater recharge inferred from land cover changes. In general, the observed amplitudes of lake-level fluctuations are larger than expected from climatic changes alone and thus underline that land cover changes in lake catchments must be considered in climatic interpretations of past lake-level fluctuations.