Calcareous groundwater raises bogs; the concept of ombrotrophy revisited

1 Raised bogs are traditionally regarded as being solely dependent upon atm ospheric influences. However, these terrestrial carbon stores may also be a ffected by calcareous (bicarbonate-rich) groundwater, which is often found in deeper peat layers. 2 Field data from a bog area in the Netherlands were used to select appropr iate levels of bicarbonate supply for an aquarium mesocosm experiment. The effects of 0, 0.1, 0.5, 1 and 2 mmol HCO3- l(-1), and 1 mmol HCO3- l(-1) 2 mmol SO42- l(-1), on the biogeochemistry of peat monoliths, including the ir Sphagnum vegetation, were investigated. 3 Slightly increased alkalinity rapidly stimulated buoyancy of living Sphag num due to higher inorganic carbon concentrations in the water layer. Moder ate HCO3- concentrations also stimulated buoyancy of the entire peat monoli ths after 3 weeks, because of increased methane production rates. High alka linity, however, led to rapid internal phosphate mobilization, pear disinte gration and Sphagnum die-off. This detrimental effect was stronger when sul phate was supplied simultaneously. 4 The results are discussed with respect to the carbon dynamics and overall functioning of peat bogs, in relation to hydrology and hydrochemistry (gro undwater influence, sulphate pollution).