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Microform‐scale variations in peatland permeability and their ecohydrological implications

The acrotelm–catotelm model of peatland hydrological and biogeochemical processes posits that the permeability of raised bogs is largely homogenous laterally but varies strongly with depth through the soil profile; uppermost peat layers are highly permeable while deeper layers are, effectively, impermeable. We measured down‐core changes in peat permeability, plant macrofossil assemblages, dry bulk density and degree of humification beneath two types of characteristic peatland microform – ridges and hollows – at a raised bog in Wales. Six 14C dates were also collected for one hollow and an adjacent ridge. Contrary to the acrotelm–catotelm model, we found that deeper peat can be as highly permeable as near‐surface peat and that its permeability can vary by more than an order of magnitude between microforms over horizontal distances of 1–5 m. Our palaeoecological data paint a complicated picture of microform persistence. Some microforms can remain in the same position on a bog for millennia, growing vertically upwards as the bog grows. However, adjacent areas on the bog (< 10 m distant) show switches between microform type over time, indicating a lack of persistence. Synthesis. We suggest that the acrotelm–catotelm model should be used cautiously; spatial variations in peatland permeability do not fit the simple patterns suggested by the model. To understand how peatlands as a whole function both hydrologically and ecologically, it is necessary to understand how patterns of peat physical properties and peatland vegetation develop and persist.