The post-glacial development of the Lake Onega coast, together with modern processes, creates conditions for the formation of complex coastal ecosystems that may be vulnerable to possible climate change and anthropogenic impacts. Such systems include wetlands extending along the eastern and southern coasts of Lake Onega. The area of a special interest is near the mouth of the Andoma River, as it combines the influence of the riverbed processes of a large river, the dynamics of the coast of Lake Onega, and peat lands development. The aim of the research was a detailed study of the structure of the Holocene deposits in the lake-river interval on the northern bank of the Andoma River, which reflects the stages of formation and variability of the natural conditions of the lakeside lowland. A reference transects including 4,800 m long GPR profile, supplemented with boreholes was created. The complex study of GPR cross-section and peat cores revealed the internal structure of the peat bog. A plateau-like uplift of the mineral base of the bog, framed by rupture zones with accompanying watercourses, was found. This area is considered as a deformation formed because of glacial dislocations or because of neotectonic deformations. Besides the main structural elements, local erosion incisions accompanied by sandy deposits, which could be confined to the buried paleochannels of the Andoma River, were found at the top of the limno-alluvial sediments. Analysis of the complex transect together with a vegetation description showed a difference in biological and environmental conditions zones, which contribute to biological diversity of the study site. In the future, the reference transects development provides a basis for the initial identification of vulnerabilities and long-term monitoring of the ecological transformation of ecosystems.
