Seasonal CO2 balances of a subarctic mire

Micrometeorological measurements of CO2 and energy fluxes were carried out in a peatland ecosystem in northern Finland (69 degrees 08'N, 27 degrees 17'E) during a measurement period from April to the end of October 1997. The summer of 1997 was exceptionally warm and dry as compared to the climatological normal period of 1961-1990, and the effects of the high temperature and lowered water table were clearly seen in the CO2 fluxes. The highest individual downward flux densities of about -0.25 mg(CO2) m(-2) s(-1) took place at the end of July, while the highest respiration rates of 0.15 mg(CO2) m(-2) s(-1) were observed later in August. During the first days of measurements in April the median of respiration flux densities through the snow cover was about 0.006 mg(CO2) m(-2) s(-1). In correspondence to the CO2 fluxes the strongest sink terms in the daily net ecosystem exchange (NEE) balances of about -6 g(CO2) m(-2) d(-1) were observed in July. The highest positive balances of about 4 g(CO2) m(-2) d(-1) were observed in early June and in August. The daily balances in April were about 0.6 g(CO2) m(-2) d(-1). The net balances for the sink period (June 15 to August 26, 1997) and for the B-month measurement period were -188 g m(-2) and -30 g m(-2), respectively. The wintertime CO2 balance was estimated by modeling the NEE using the NEE values from the first measurement week in April. The wintertime balances obtained yielded estimates for annual balances in the range of 62 to 72 g m(-2) yr(-1).