Extreme weather event responses of collocated forest, lake and peatland ecosystems

The frequency and intensity of extreme weather events (EWEs) have increased in recent decades and are projected to continue rising globally. The impact of EWE on boreal ecosystems can be disproportionate. In forests, the exchange of CO₂  is affected by droughts depending on their timing and severity. In lakes, heatwaves might strengthen stratification and trigger oxygen depletion, with consequences on greenhouse gas (GHG) dynamics. Excessive heat and winds can also increase GHG emissions from peatlands and lakes. The driving mechanisms of GHG exchange in these three ecosystems differ, and their responses to EWE also vary. 

Long-term flux data, obtained with the Eddy covariance (EC) technique, enable us to establish a baseline response and analyse how these different ecosystems react to EWE. The EC technique measures the vertical exchange of gases, particles, and energy at an ecosystem scale, with a 30-minute interval, demonstrating the instantaneous response of the ecosystem.

Here, we analysed the effect of EWE on GHG dynamics from adjacent forest (Hyytiälä), lake (Kuivajärvi) and peatland (Siikaneva) ecosystems, where long-term EC flux measurements are available. EWE, such as heatwaves, dry spells, excessive rainfall, prolonged high wind spells, and compound events, have been identified in the last decade using both in situ and ERA5 reanalysis Land hourly datasets. The ecosystems exhibit contrasting responses to the EWEs. For instance, during the 2018 heatwave, the forest exhibited enhanced CO₂ uptake, while both the lake and the peatland showed increased emissions relative to the reference period (2013-17).