Hydrology and dissolved organic carbon biogeochemistry in an ombrotrophic bog

At the Mer Bleue bog, Ontario, Canada, DOC export measured at the basin outflow was −8·3 ± 3·7 g C m −2 yr −1 , and DOC loading via precipitation was estimated to be 1·5 ± 0·7 g C m −2 yr −1 . Discharge and DOC export calculated using a Dupuit–Forchheimer approximation compared well (within 1 g C m −2 yr −1 ) to outflow estimates of DOC export, and confirmed that outflow measurements were a suitable proxy for DOC seepage at the peatland margins. DOC export was 12% of the magnitude of the residual carbon sink measured at the peatland. The [DOC] across groundwater transects decreased with depth, and [DOC] sampled below 0·75 m depths remained fairly constant over the study period. However, [DOC] exported through the acrotelm (0 to 0·45 m peat depth) was variable, ranging from 40 mg l −1 after snowmelt to 70 mg l −1 during the growing season. Fluorescence analysis revealed that exported DOC was ‘allochthonous‐like’, whereas DOC in the catotelm (deeper layers of peat) became more ‘autochthonous‐like’ with depth. A conceptual model is developed to summarize the hydrological processes and controls which affect DOC biogeochemistry at the Mer Bleue.