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

Nature Geoscience (Impact Factor: 11.74). 11/2008; 1(11). DOI: 10.1038/ngeo331
Source: OAI


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

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Available from: Takeshi Ise
    • "Thus, in addition to a long-term trend of increased water loss from increased evapotranspiration, there exists the potential for multi-year droughts, some of which are likely to be severe (Michaelian et al., 2011; Wang et al., 2014). Water table declines within peatlands could be substantial during prolonged droughts, resulting in substantial losses of peat through multiple mechanisms (Ise et al., 2008; Zhaojun et al., 2011). "

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    • "However, we did not observe a significant trend of Q 10 along the wetland degradation gradient. In a study of peatlands in northern Manitoba, Canada, Ise et al. (2008) found that a falling water table increased the sensitivity of peat decomposition to temperature. Soil water content in the alpine wetlands was high, which depressed air diffusion, enzyme activity, and substrate availability (Rey et al. 2005; Tang et al. 2012; Wang et al. 2010); this may have obscured the influences of increasing temperature and resulted in a lack of significant differences in Q 10 among different alpine wetlands. "
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    ABSTRACT: Alpine wetlands are considered to be very sensitive to future climate warming. Understanding changes in decomposition rates (Rs) of soil organic matter (SOM) and temperature sensitivity (Q 10) in alpine wetlands, under the scenarios of a warming climate and decreasing soil moisture, is important for predicting their carbon (C) budget. Here, we established three sampling transects from wetland edge to meadow in the Zoige alpine wetlands in China, which represented the gradients of decreasing soil moisture. We conducted an incubation experiment (5–25 °C) to explore changes in Q 10 with the degradation process from alpine wetland to alpine meadow. The results showed that temperature significantly influenced Rs in all locations. Rs first increased from site I to site IV and then decreased from site IV to site V. However, Q 10 and activation energy (E a ) showed no apparent trends with soil coming from sites along a moisture gradient. Overall, the Q 10 values in the wetland (sites 1.50) were significantly lower than that of the meadow (1.83); similar trends were observed for E a . In addition, E a exhibited a negative logarithmic relationship with C quality indices in all locations, which suggested that the C quality-temperature hypothesis is applicable to both alpine wetlands and meadows. These findings provide a theoretical foundation for predicting the potential influences of warming climate on soil C turnover and storage in alpine wetlands.
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    • "relatively depressed because of water-saturated, anoxic conditions (Clymo, 1984; Ise et al., 2008). For reed-dominated wetlands , the transport and deposition of particulate matter, including mineral and organic sediment, is accentuated at and near the wetland margin. "
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    ABSTRACT: Knowledge of the millennial abrupt monsoon failures is critical to understanding the related causes. Here, we extracted proxy indices of Indian Summer Monsoon (ISM) intensity during the early to mid-Holocene, from peat deposits at Lake Xihu, in southwestern China. There are a series of abrupt, millennial-scale episodes of ISM weakening inferred from the Lake Xihu records, which are generally synchronous with those inferred from other archives over ISM areas. An important feature is that the ISM failures inferred from the Lake Xihu proxy indices synchronize well with abrupt changes in solar activity. We argue that changes in solar activity play a primary role in producing most of these millennial ISM failures, while some other causes, including freshwater outbursts into the North Atlantic Ocean and changes in sea surface temperatures of the eastern tropical Pacific Ocean, may have also exerted influences on parts of the millennial ISM failures.
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