Modelling of hydrological and thermal controls on carbon dioxide exchange at Mer Bleue bog

The main purpose of this research was to understand hydrological and thermal controls, and their effects on bog net ecosystem productivity and its components. This purpose was achieved by means of the process-based modelling.;Water table drawdowns induced drying in the macroporous near-surface hummock peat that resulted in decrease of the near-surface microbial respiration, which offset increased microbial and root respiration at depth with improved aeration. Furthermore, increased hollow soil respiration with water table drawdowns was offset by decreased moss aboveground respiration at hummocks with near-surface drying. So, ecosystem respiration at Mer Bleue bog was conservative to subsurface hydrology.;Soil respiration in hummocks was sensitive to water table variation. The highest respiration occurred at intermediate water tables and declined as the water table moved up or down. Depending on whether the differences in respiration under different water table depths were less or more than the random error of measurements, some peatlands would be conservative to the local hydrology, like Mer Bleue bog, while others would not.;Vascular gross primary productivity was little affected by subsurface hydrology during dry periods of low water tables as vascular roots extended below the zone of near-surface desiccation. However, near-surface desiccation caused decrease in moss gross primary productivity and thus in bog gross primary productivity. With conservative response of ecosystem respiration, subsurface hydrology affected net ecosystem productivity mainly through gross primary productivity at Mer Bleue bog. The water table and near-surface peat water contents were some of the most important factors in explaining bog net ecosystem productivity and its interannual variability.;Preferential gravitational flow through high macropore fractions of the fibric peat, complementary to the matrix flow, explained well rapid water infiltration and low water retention in this peat. Hummocky microtopography influenced peat temperatures at depth and ground heat fluxes at surface by inducing natural air convection within the fibric peat in hummock mounds with high air-filled porosities. Natural air convection, determined by high permeabilities to air of the macroporous and well-drained fibric peat and driven by temperature differences between peat surface and interior, enhanced heat transfer in hummocks and also in neighbouring hollows.