Abstract. Dissolved fluxes of C which are an important component of the global C budget of peatlands may be affected by global change in different ways. The evolution of peatland vegetation is an issue caused by the indirect effect of global change that still needs to be addressed. The aim of this study was to study the temporal and spatial variations in the quantity and the characteristics of dissolved C within in a peatland stream continuum, the peatland being invaded by Molinia caerulea and Betula spp.

The study highlighted the following key points:

(i) Vegetation change tends to increase the DOC concentration of peat surface water.

(ii) DOC exports were in the range of those found in the literature, and it was clearly established that peatland DOC can reach second order streams.

(iii) Peat water was supersaturated in CO₂ especially in summer during the peak of microbial activity.

(iv) the CO₂ critical layer at the surface of the soil may promote CO₂ excess build-up in the peat water. This critical layer may promote CO₂ export out of the peatland.

The effect of vegetation change on the DOC content of peat water deserves further attention as it may have a deep impact on downstream river water quality. In particular, it is necessary to clarify whether the concentration of C dynamics is affected by the invading species. More attention should be paid to hydrological processes (e.g. pumping capacity of the different plants) and the microbial activity in the rhizosphere of the invading plants. Also, the relation between the CO₂ critical zone at the surface of the soil and the CO₂ concentration in water should be studied in detail.