Influence of palaeoenvironmental changes on the formation of the Vilku bog deposits

Influence of palaeoenvironmental changes on the formation of the Vilku bog deposits 

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Elina Reire 

Laimdota Kalnina 0000-0002-2802-7139 

Aija Cerina 0000-0003-2176-3309 

Latvijas Universitāte 

Email: elinareire@inbox.lv 

DOI: 10.22364/fg.21.7 

Abstract  

Keywords: Lubāns Plain, gyttja, peat, plant macroremains, AMS ¹⁴C 

Vilku Bog is a small (about 95 ha) area of peatland formed in a glacial meltwater lake depression in the north-western part of the Lubāns Plain. The aim of this study was to investigate the influence of paleoenvironmental changes on the sedimentation of Vilku Bog. To achieve this aim, fieldwork was carried out – eight soundings were taken and three boreholes were drilled diagonally across the Vilku Bog. Multidisciplinary studies were carried out on deposit samples collected during fieldwork. The deposits were subjected to analyses of Loss on Ignition, plant macroremains, analyses of peat botanical composition and peat decomposition degree, spore-pollen analyses, and radiocarbon AMS ¹⁴C dating.  

The area where Vilku Bog is located was originally filled with lake clay and silt, but during the Middle Holocene, at the climatic optimum of 6160 cal BP, the lake began to accumulate gyttja and peaty gyttja as the number of aquatic plants increased. This contributed to the lake becoming completely overgrown and the start of peatland formation before 5810 cal BP in the second part of the Middle Holocene. The development of Vilku Bog started with the accumulation of peat deposits over the lake gyttja (fen-type Hypnum, grass and sedge peat, transition-bog-type grass peat and Sphagnum- cotton grass peat), followed by raised-bog-type peat (Sphagnum peat). The conditions (peat decomposition) of deposit accumulation were variable during the development of the bog. Peat botanical composition, which is affected by water-level fluctuations, indicate that Vilku Bog underwent the complete cycle of bog development, from fen to transitional bog and finally to raised bog. It has only been developing as a raised bog for the past 380 years.