Effects of temperature rise and water-table-level drawdown on greenhouse gas fluxes of boreal sedge fens

As potential outcomes of climate change, we examined the effects of environmental warming and drying on instantaneous CO2, CH4 and N2O fluxes in three sedge fens situated in the northern and middle boreal zones. Warming was induced by means of open top chambers (OTCs) and drying through drainage via ditching. OTCs raised the air temperature by 0.2–2 °C, whereas short-term drainage dropped the water-table level (WTL) by 5–10 cm and long-term drainage by 10–30 cm. The impact of simulated warming was rather negligible as warmer and drier conditions caused net ecosystem exchange (NEE) to decrease only at one of the two mid-boreal sites. Otherwise, the temperature rise alone or paired with WTL drawdown did not alter gas fluxes at any of the sites. Instead, the drainage effect overrode that of warming. Primarily WTL drawdown accounted for the differences in fluxes detected, but this was more apparent at the mid-boreal sites than our northern-boreal one. Notably, the northernmost Lompolojankka sedge fen, which was both the coolest and wettest of the three sites, was least sensitive to temperature rise and drainage; there, only CH4 emissions were affected by WTL drawdown.