Long-term net
ecosystem CO₂ exchange measurements were conducted on a nutrient-rich
fen in northern Finland using the eddy covariance method. During the three
measurement years (2006–2008), the mean daytime CO₂ flux in July was
–0.40 mg CO₂ m^–2 s^–1, while in mid-winter
(January–March) the mean efflux was 0.008 mg CO₂ m^–2
s^–1. Annual balances of –12, –123 and –216 g CO₂
m^–2 a^–1 were observed in 2006, 2007 and 2008,
respectively. It is suggested that the low uptake in 2006 was related to the
warm and dry conditions during the growing season and the consequent reduction
in vegetation activity. When compared with two other fens in Finland, there was
a clear correspondence between the nutrient status, mean pH value, maximum LAI
and the mid-summer CO₂ uptake. A similar pattern was not seen in the
annual CO₂ balance, which correlates more with the growing season
length.