Disentangling the drivers for the development of a Baltic bog during the Little Ice Age in northern Poland

Abstract

This paper presents the results of multi-proxy research (pollen, plant macrofossil, testate amoebae and bulk density) on a 100-cm core collected from a Baltic raised bog in N Poland. The impact of the variability of the climate as well as human disturbance in the last 650 years on the development of the peat bog Kusowskie Bagno is described. Based on the results, the development of the raised bogs to the south of the southern coast of the Baltic Sea during the Little Ice Age occurred differently than in NW Europe. In NW Europe (e.g., Great Britain, Ireland, Denmark and N Germany) during the periods of climate cooling associated with lower solar activity, there was a characteristic wet phase, whereas N Poland was characterised by a dry phase. In the years AD 1450–1500, AD 1640–1720 and AD 1810–1840, which correlate with the periods of lower solar activity (the Spörer, Maunder and Dalton minima) and the periods of lower temperatures in Europe, the water table in Kusowskie Bagno decreased, and this was followed by changes in the vegetation. The largest drop in the water table occurred in the years AD 1640–1720. The dry phase resulted in the reduction of the population of Archerella flavum and Amphitrema wrightianum, which are organisms that are typical of wet habitats, and the appearance of, e.g., Arcella artocrea and Phryganella acropodia, which are indicators of dry habitats. The humidity decline halted the growth of Sphagnum sec. Cuspidata (Sph. cuspidatum and Sph. balticum) and Sphagnum magellanicum. At the same time, Eriophorum vaginatum, Baeothryon caespitosum and Pinus sylvestris appeared, and a dramatic increase in the bulk density is also observed. Since AD 1720, when the solar activity and the water table increased, the bog regenerated, and the population of Sphagnum fuscum/capillifolium developed. The development of the studied raised bog depended mainly on climate change. The increasing human impact in the area, which started in approximately AD 1320 and lasted for several centuries, was manifested in deforestation and in the increase in the surface area of farmland. However, this result did not have a significant impact on the development of the peat bog.