Northern peatlands faced compounding disturbances that transformed such critical ecosystems from long-term carbon sinks into carbon sources. Considerable investment is therefore directed for restoring their carbon sequestration potential through large-scale rewetting/rehabilitation. However, rapid need to transform their carbon dynamics contrasts with millennial timescales over which peat profiles that control key ecohydrological processes within these ecosystems have developed. This study demonstrates the sensitivity of vadose zone hydrology of northern peatlands to hydrophysical properties of the very near-surface peat layer and therefore the potential capability of at least some ecohydrological processes to respond rapidly to developments in peat properties as a result of restoration. HYDRUS 1-D Monte Carlo simulations were undertaken of near-surface peat layers of various species and depths overlying degraded peat layer during periods of sustained drying. The modelling results showed that shallow additions of newly developed Sphagnum peat, just a couple of centimetres in depth, substantially modified near-surface hydrology of peat profiles and significantly altered the time taken for reaching important ecohydrological pressure heads. Whilst a degraded peat layer reached threshold pressure head (TP) of −100 cm in 119 h, addition of 2.5-cm layer of S. magellancium reduced the average time to TP by 18 hours, whilst S. fuscum and amalgamated Sphagnum overlying degraded peat across initial WTDs (5, 10, 15 and 20 cm) increased average time to TP by 304 and 540 h, respectively. This demonstrates that whilst peat hydrophysical properties have developed over millennia, ecohydrological dynamics of these systems rapidly adjusted through restoration approaches in response to disturbances.
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