CO2 exchange of a sedge fen in southern Finland -: The impact of a drought period

Eddy covariance (EC) measurements of net ecosystem CO2 exchange (NEE) were conducted on a boreal sedge fen in southern Finland (61 degrees 50 ' N 24 degrees 12 E) during a 1.5-yr period covering two summers in 2004-2005. The EC data were complemented by chamber measurements, which enabled the partition of the daytime NEE into respiration and photosy tithes is. A special emphasis was put on the hydrometeorological responses of CO, exchange during a drought period in July 2005. A mean CO2 efflux Of 0.009 mg CO2 m(-2) s(-1) was observed during mid-winter(January-February). while the night-time respiration during the two Julys averaged 0.09 mgCO(2) m(-2) s(-1). During both years the mean mid-day uptake in late July was about -0.16 mCO(2) m(-2) s(-1). An annual CO2 balance of -188 CO2 m(-2) was observed in 2005. A slightly higher net sink of -219 gCO(2)m(-2) was estimated for 2004. The drought period experienced in July 2005 caused a clear depression in the daily NEE values. From the combined analysis of EC and chamber measurements it was concluded that this was mainly due to increased respiration. but evidence was also found of suppressed photosynthesis due to a high VPD.