Chironomidae (Insecta: Diptera) succession in Żabieniec bog and its palaeo-lake (central Poland) through the Late Weichselian and Holocene

Subfossil Chironomidae assemblages were studied in a sediment sequence from Żabieniec bog in central Poland. The climate history and habitat changes in the palaeo-lake were reconstructed from these assemblages. Currently no chironomid-based climate calibration set is available from Poland and so past mean July air temperatures were inferred from chironomid-climate calibration data-sets from Norway, Russia, and Switzerland. During the Late Weichselian the three calibration functions from these data-sets provided similar temperature inferences but there was some divergence in the reconstructions for the Younger Dryas and Holocene. In the late Pleniglacial, inferred summer air temperature was relatively low (8–12 °C) and the lake was oligotrophic. At about 16.5 ka BP, temperature rapidly rose to 15 °C and assemblage diversity substantially increased. During the interstadial, temperature stayed at this level. In the Younger Dryas, July air temperature was only 1–2 °C lower than in the interstadial, as inferred from the Norwegian calibration data-set, whereas the Russian and Swiss calibration functions did not indicate any temperature decrease. From the beginning of the Holocene, taxa typical of meso-eutrophic conditions dominated. There was an increased abundance of phytophilous species and the assemblage composition was also influenced by changes in water-level. Palaeotemperature reconstructions differed in their values. From 8.0 to 8.7 ka BP, inferences based on the Swiss and Russian data-sets indicated a cold oscillation while reconstructions based on the Norwegian data-set did not show any temperature decrease. After 2.5 ka BP assemblage diversity and head-capsule concentrations decreased. In the last millennium semi-terrestrial taxa dominated, except from Late Medieval to Early Modern times when shallow-water species reappeared.