%0 katsaus %T Changes in the open water hollows in Häädetkeidas and Kauhaneva mires during 1947–2017 based on remote sensing %A Talvitie, Pasi %A Räsänen, Aleksi %A Silvan, Niko %D 2023 %J Suo - Mires and peat %V 74 %N 1-2 %U http://suo.fi/article/10822 %X

Raised bogs are the most common combined mire type in Southern Finland. They are dependent on precipitation to provide water and nutrients. The surface of the raised bog is characterized by dry ridges, hummocks, and wet depressions, hollows. Climate warming reduces winter snowfall and increases evaporation, which is estimated to lower the water level in raised bogs. This can cause changes in the local ecosystem and accelerate climate warming locally. However, relatively little research has been done on long-term changes in raised bogs.
In this work, changes in the amount and area of open water hollows is determined over the course of 70 years with the help of aerial and satellite images. The research sites are two raised bogs in Western Finland: Häädetkeidas mire and Kauhaneva mire. Long-term change is monitored using object-based segmentation and supervised maximum likelihood classification of aerial images. Short-term change during a single growing season is determined using satellite images and maximum likelihood classification. The results are compared to weather data from the area.
Based on the results, the number and surface area of open water hollows have varied during the review period. From the 1940s to the 1970s, there has been an increase in surface areas and numbers, after which they have decreased. Compared to the situation in the 1940s, the number of springs in Häädetkeidas mire has decreased by 13.8% and the area has decreased by 14.8%. In Kauheneva mire, the number has decreased by 5.3% and the area has decreased by 6.3%. At the same time, the average temperature in the area has risen by more than 1 °C. However, based on satellite image analysis, the variation during a single growing season can be strong, which causes uncertainty in the interpretation of long-term changes.
The results show that both long-term and short-term surface structure changes detectable by remote sensing methods are taking place in the raised bogs. The changes are probably connected to the change in climate conditions.