Indicative effects of climate change on groundwater levels in Estonian raised bogs over 50 years

Analyses of 50-year (1962-2011) monthly air temperature and precipitation data indicated substantial climate change in the locations of two raised bogs (Linnusaare and Mannikjarve) in central-east Estonia. During recent years the cross-year winter air temperature increased by 1.7 degrees C, while the cold-season precipitation increased by 4 mm. The fluctuation amplitude of temperature and precipitation values decreased. Snow depth proved to be the most sensitive variable to winter warming, followed by groundwater levels together with mean and maximum soil frosts. Long-term groundwater levels on the domes of the bogs and in the forested/treed lagg areas were 0.3-0.4 m and 0.4-0.8 m below the soil surface, respectively. Warming caused changes in groundwater level amplitude of 3-22 cm in the bog domes and 3-14 cm in the forested lagg zones. The lowest groundwater levels in ridge-pool ecotopes at Mannikjarve rose by 6-10 cm (i.e. these ecotopes became wetter); but the incidence of low groundwater levels increased in most ecotopes, indicating a more general trend towards drier conditions in the bog.