Processes affecting lateral carbon fluxes from drained forested peatlands

Lateral carbon (C) flux results from complex interplay of formation, transport and biodegradation of dissolved organic carbon (DOC), and is an important but rather scarcely studied component of the C balance in peatlands. Temperature and water table (WT) are the primary factors regulating peat CO₂ emissions and the release of DOC. DOC dynamics in soil is complicated because the DOC storage is continuously increased by the decomposition of solid organic matter, but simultaneously decreased by biodegradation. Any upscaling of lateral C fluxes requires understanding these coinciding processes. We studied the effect of temperature and WT on CO₂ emission and DOC concentration in pore water while incubating peat columns (diameter 0.2 m height 0.5 m) in laboratory conditions for eight months. Peat columns were extracted from drained forested peatlands in Finland, Estonia, Sweden and Ireland. WT was set to -0.2 m and -0.4 m distance from the column upper end. During the incubation, the temperature ranged between 18  and 34 ⁰C. DOC samples were extracted in monthly intervals from the columns using Rhizon soil water samplers. At the same time CO₂ emission was measured from the headspace of the column. DOC biodegradation to CO₂ and its temperature sensitivity was studied by incubating soil water samples in controlled conditions. The quality (aromaticity) of DOC was investigated with a UV-VIS spectrophotometer. The effect of temperature on DOC concentration was not straightforward unlike in the case of CO₂ emission. DOC concentration increased steepest when the temperature exceeded 25  ⁰C, whereas with lower temperatures DOC was unchanged or slightly decreased. This can be due to different temperature sensitivities of DOC release and its biodegradation. Low WT resulted in high CO₂ emissions and DOC concentrations. These results are important in developing ecosystem models accounting for lateral C fluxes and the effects of forest management, drainage and climate change in managed peatlands.