High water table can lower a methane emission from soil Yugra State University

Climate models predict that the precipitation will increase under 2×CO2 scenario leading to raised water tables at some regions. The position of the water table within a peatland can have a large effect on CH4 emissions. Methane production occurs below the depth of the water table in anaerobic peat. Hence, the greater part of the peat profile that was anaerobic, the greater would be the expected flux. However depth of the water table affects the methane emission with complex interactions, so the effects of temporal variations in the water table level on methane emissions may be controversial. Methane emissions correlated negatively with depths of the water tables in some measurements: high methane emissions were associated with low water tables and vice versa. The suppression of methane emission by
a) filling the unsaturated pore space in peat during precipitation and the increased release rate (caused by a declining water table) could explain the result in time scale of some few days;
b) suppression of a plant-mediated mechanism of methane emission during super-high water table could explain the result in any time scale (the products of photosynthesis lead to increased root exudations which then promote the microbial formation of methane at depth; this methane is transported via the plant vascular system to the atmosphere; thus both plant-mediated methane production and transport are suppressed by high water table).
Also a drop in atmospheric pressure correlates with a precipitation. Hence, the greater part of the methane that was released during pressure dropping, the smaller would be the expected flux after precipitation (in condition of high water table).
The author acknowledge the financial support by the European Union FP7-ENV project PAGE21 under contract number GA282700.

Key words: Mires, Methane flux, Water table level, Mathematical models.

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