Carbon Accumulation and the Possibility of Carbon Losses by Vertical Movement of Dissolved Organic Carbon in West Siberian Peatlands

We studied peat stratigraphy at the Mukhrino peatland, which is a typical ombrotrophic bog for the middle taiga zone of Western Siberia, to gain insights about its history, hydrology and carbon fluxes. Seven cores were collected from locations chosen to represent the typical present-day vegetation types, for dating of separated dissolved (DOC) and particulate (POC) organic carbon fractions using the Accelerator Mass Spectrometer (AMS) radiocarbon ($^{14}$C) method. The oldest peat was found at the bottoms of an underlying lake (10,053 cal. year BP) and an ancient riverbed (10,989 cal. year BP). For the whole history of the peatland the average peat accumulation rate was estimated to be 0.067±0.018 cm yr-1 (0.013-0.332 cm yr-1) and the carbon accumulation rate was 38.56±12.21 g m-2yr-1 (28.46–57.91 g m-2 yr-1). There were clear age differences between the separated samples of DOC and POC. DOC was older than POC in the uppermost 150 cm of the peat deposit, and younger in the deeper layers. The difference in age increased with depth, reaching 2,000–3,000 years at the bottom of the peat deposit (depth 430--530 cm). Following consideration of a range of factors that could potentially cause the dating discrepancy, we hypothesised that DOC continuously moves down into the mineral sediment beneath the peat, as an additional carbon flux that results in mixing of younger and older carbon. On this basis we estimated the apparent rate of DOC downward movement and the associated rate of carbon loss. The first estimate of the average rate of DOC downward movement in Western Siberia is 0.047±0.019 cm yr-1.