High sensitivity of peat decomposition to climate change through water-table feedback

Historically, northern peatlands have functioned as a carbon sink, sequestering large amounts of soil organic carbon, mainly due to low decomposition in cold, largely waterlogged soils. The water table, an essential determinant of soil-organic-carbon dynamics interacts with soil organic carbon. Because of the high water-holding capacity of peat and its low hydraulic conductivity, accumulation of soil organic carbon raises the water table, which lowers decomposition rates of soil organic carbon in a positive feedback loop. This two-way interaction between hydrology and biogeochemistry has been noted but is not reproduced in process-based simulations. Here we present simulations with a coupled physical–biogeochemical soil model with peat depths that are continuously updated from the dynamic balance of soil organic carbon. Our model reproduces dynamics of shallow and deep peatlands in northern Manitoba, Canada, on both short and longer timescales. We find that the feedback between the water table and peat depth increases the sensitivity of peat decomposition to temperature, and intensifies the loss of soil organic carbon in a changing climate. In our long-term simulation, an experimental warming of 4 °C causes a 40% loss of soil organic carbon from the shallow peat and 86% from the deep peat. We conclude that peatlands will quickly respond to the expected warming in this century by losing labile soil organic carbon during dry periods.Earth and Planetary SciencesOrganismic and Evolutionary Biolog

Distribution patterns of selected PAHs in bulk peat and corresponding humic acids from a Swiss ombrotrophic bog profile.

An ombrotrophic peat core was collected in 2005 from Etang de la Gru\ue8re, Jura Mountains, Switzerland. The concentrations of nine among the U.S. Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) (i.e., acenaphthene, phenanthrene, fluorene, pyrene, fluoranthene, benzo[jbk]fluoranthene, benzo[a]pyrene, benzo[ghi] perylene, and indeno[1,2,3-cd]pyrene) were determined in both bulk peat and corresponding humic acids (HA) samples by gas chromatography equipped with a mass spectrometry detector (GC-MS). The maximum PAHs concentrations in peat (around 1,250 \u3bcg \u3a3 PAHs kg 121 dry matter) were found at 28\u201330 cm of depth, which correspond to ca. 1920\u2013 1930, when coal inputs to Switzerland reached their maximum level. Amongst the nine PAHs analyzed in the peat samples, pyrene (Pyr) was the predominant species, accounting for ca. 20\u2013100% of the total PAHs throughout the profile. In the HA fraction, that represents 24.7% (average value) of the bulk peat, only phenanthrene (Phe), and sporadically Pyr and fluoranthene (Fth), were detected. In particular, HA showed Phe concentrations that were ten\u2013150 times higher than corresponding bulk peat samples, thus suggesting its preservation against biodegradation due to the incorporation into HA molecules