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

Nature Geoscience (Impact Factor: 11.67). 11/2008; DOI: 10.1038/ngeo331
Source: OAI

ABSTRACT 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 Sciences Organismic and Evolutionary Biology Version of Record

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, δ13C, biogenic silica, and XRF elemental data) study of a 1.5 m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS 14C ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170–AD 370, AD 800–960, and after AD 1450; and a weakening of the summer monsoon between AD 370–800, and AD 1300–1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35°N between BC 170–AD 370 and AD 800–960, whereas it likely did not reach above 17°N during the drought intervals of AD 370–800 and AD 1300–1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.
    Quaternary Science Reviews 03/2015; 111. DOI:10.1016/j.quascirev.2015.01.007 · 4.57 Impact Factor
  • Source
    The Holocene 01/2015; DOI:10.1177/0959683614566252 · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Continuous measurements of ecosystem scale evapotranspiration (ET) were obtained using the eddy covariance method over the 2010 and 2011 growing seasons (May-September) at three adjacent peatlands that have undergone long-term water table manipulation. The three (wet, dry and intermediate) sites represent peatlands along a hydrological gradient, with different average depths to water table (WTD) and different resulting vegetation and microform assemblages. The 2010 growing season was warmer and wetter than normal, while 2011 conditions were near normal. The difference in maximum daily ET values (95th percentiles) between sites were greater in 2010 (3.14 mm d(-1) -4.17 mm d(-1)) compared to 2011 (3.68 mm d(-1) -3.95 mm d(-1)), yielding cumulative growing season ET that followed the wet to dry gradient in both 2010 and 2011. Synoptic weather conditions (i.e. air temperature, vapour pressure deficit, and incoming solar radiation, etc.) could not explain differences in ET between sites due to their proximity to one another. Peat surface wetness was more spatially homogeneous at the wet site due to small average microtopographic variations (0.15 m) compared to the intermediate (0.30 m) and dry (0.41 m) sites. Although average Bowen ratios were less than one at all three sites, greater surface wetness and heating at the wettest site lead to differences in energy partitioning, with higher average Bowen ratios at the sites with a shallow average WTD. No significant relation between normalized ET and WTD was found at any of the sites that were consistent across both study years. In addition, the lack of a relation between ET and near-surface moisture suggests that the unsaturated hydraulic conductivity and the boundary layer resistance created by the vascular canopy combined with low surface roughness limits evaporative losses from the peat surface. This study suggests that the low ET of a dry site compared to a wet site may be due to the impact of a long-term change in WTD on leaf area and the relative distribution of plant functional groups.
    Agricultural and Forest Meteorology 09/2013; 178-179:106-119. DOI:10.1016/j.agrformet.2013.04.013 · 3.89 Impact Factor

Full-text (2 Sources)

Available from
May 20, 2014