Inter-annual variability in water table depth controls net ecosystem carbon dioxide exchange in a boreal bog

The net ecosystem carbon dioxide (CO2) exchange (NEE) between boreal bogs and the atmosphere and its environmental drivers remains understudied despite the large carbon store of these northern ecosystems. We present NEE measurements using the eddy covariance technique in a boreal ombrotrophic bog over five growing seasons and four winters. Inter-annual variability in CO2 uptake was most pronounced in June-September (-4 to -122 g CO2-C m(-2)), less in March-May (-1 to -21 g CO2-C m(-2)) and very small in October-November (-2 to -4 g CO2-C m(-2)). Variability in NEE between years was linked primarily to changes in water table depth (WTD). Strong and significant relationships (r(2) > 0.89, p a parts per thousand currency sign 0.05) were found between summer (June-September) maximum photosynthetic rate (A (max)), net ecosystem productivity (NEP), gross ecosystem productivity and WTD. Adding air temperature through multiple regression analysis further increased correlation between summer A (max), NEP, and WTD (r(2) = 0.96, p = 0.05). In contrast to previous studies examining controls on peatland CO2 exchange, no relationships were found between productivity or cumulative exchange and early season temperature, timing of the snowmelt or growing season length.