Shoreline and Surface Area Changes Induced by Floating Islands in Peatland Lakes (Tuchola Pinewood Forest, Poland)

Multitemporal aerial photography and topographic maps were applied to investigate shoreline and surface area changes induced by floating islands in three small (area < 1 ha) peatland lakes in the Tuchola Forest. The observation period covers the last 60 years (1951–2011). Shorelines of peatland lakes are stable, unless parts of them detach as floating mats and become floating islands which could have migrated sporadically in the past. Currently, they are rooted permanently to the mat (Dury I and Dury V Lakes) or float loose (Kozie Lake). In the observation period, movement of the islands and closing of lake bays due to overgrowing were the main reasons of shoreline changes. Due to low resolution of old aerial photographs, other changes are not decipherable and can be treated as negligible. Therefore, no reasonable conclusions can be drawn regarding the actual floating mat encroachment during the last 60 years, and the rate of lake shrinking, based of aerial photographs.