Carbon dioxide exchange on a northern boreal fen

Long-term net ecosystem CO{sub 2} 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 CO{sub 2} flux in July was -0.40 mg CO{sub 2} m-2 s-1, while in mid-winter (January-March) the mean efflux was 0.008 mg CO{sub 2} m-2 s-1. Annual balances of -12, -123 and -216 g CO{sub 2} 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 CO{sub 2} uptake. A similar pattern was not seen in the annual CO{sub 2} balance, which correlates more with the growing season length. (orig.)