Calcareous groundwater raises bogs; the concept of ombrotrophy revisited

1 Raised bogs are traditionally regarded as being solely dependent upon atmospheric influences. However, these terrestrial carbon stores may also be affected 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 appropriate levels of bicarbonate supply for an aquarium mesocosm experiment. The effects of 0, 0.1, 0.5, 1 and 2 mmol HC[[O.sub.3].sup.-] [1.sup.-1], and l mmol HC[[O.sub.3].sup.-] [1.sup.-1] + 2 mmol S[[O.sub.4].sup.2-][1.sup.-1], on the biogeochemistry of peat monoliths, including their Sphagnum vegetation, were investigated. 3 Slightly increased alkalinity rapidly stimulated buoyancy of living Sphagnum due to higher inorganic carbon concentrations in the water layer. Moderate HC[[O.sub.3].sup.-] concentrations also stimulated buoyancy of the entire peat monoliths after 3 weeks, because of increased methane production rates. High alkalinity, however, led to rapid internal phosphate mobilization, peat disintegration and Sphagnum die-off. This detrimental effect was stronger when sulphate 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 (groundwater influence, sulphate pollution). Keywords: bicarbonate, carbon dioxide, eutrophication, hydrology, methane, peatlands, sulphur, Sphagnum