Comparative ecosystem-atmosphere exchange of energy and mass in a European Russian and a central Siberian bog II.: Interseasonal and interannual variability of CO2 fluxes

Net ecosystem-atmosphere exchange of CO2 (NEE) was measured in two boreal bogs during the snow-free periods of 1998, 1999 and 2000. The two sites were located in European Russia (Fyodorovskoye), and in central Siberia (Zotino). Climate at both sites was generally continental but with more extreme summer-winter gradients in temperature at the more eastern site Zotino. The snow-free period in Fyodorovskoye exceeded the snow-free period at Zotino by several weeks. Marked seasonal and interannual differences in NEE were observed at both locations, with contrasting rates and patterns. Amongst the most important contrasts were: (1) Ecosystem respiration at a reference soil temperature was higher at Fyodorovskoye than at Zotino. (2) The diurnal amplitude of summer NEE was larger at Fyodorovskoye than at Zotino. (3) There was a modest tendency for maximum 24 h NEE during average rainfall years to be more negative at Zotino (-0.17 versus -0.15 mol m(-2) d(-1)), suggesting a higher productivity during the summer months. (4) Cumulative net uptake of CO2 during the snow-free period was strongly related to climatic differences between years. In Zotino the interannual variability in climate, and also in the CO2 balance during the snow-free period, was small. However, at Fyodorovskoye the bog was a significant carbon sink in one season and a substantial source for CO2-C in the next, which was below-average dry. Total snow-free uptake and annual estimates of net CO2-C uptake are discussed, including associated uncertainties.