Raised bogs are important ecohydrological systems in which there are strong two-way links between plant succession, litter and peat decay, and hydrological functioning. Using recently established protocols, we measured the hydraulic structure of a raised bog in West Wales. We tested two hypotheses: (i) that the hydraulic conductivity (K) of the peat shows depth dependency such that lower layers of peat are effectively impermeable, and (ii) that the K of the marginal peat of the bog dome is lower than that in central areas. From 107 piezometer measurements we found there was depth dependency of K but that lower peat layers were not poorly permeable or impermeable. We also found that the K of the peat on the margin of the bog dome was generally significantly lower than that in central areas. Our results suggest that, for some bogs at least, it is important to simulate water flow through deeper peats when simulating peatland development or growth. They also raise the intriguing possibility that the low K of marginal peat is important in maintaining wet conditions in central bog areas, allowing bogs to reach greater thicknesses than they would do in the absence of the low-K margin; an idea first proposed for blanket bogs by Lapen et al. (2005).

Shallow water tables protect northern peatlands and their important carbon stocks from aerobic decomposition. Hydraulic conductivity, K, is a key control on water tables. The controls on K, particularly in degraded and restored peatlands, remain a subject of ongoing research. We took 29 shallow (~50 cm) peat cores from an estuarine raised bog in Wales, UK. Parts of the bog are in close-to-natural condition, while other areas have undergone shallow peat cutting for fuel and drainage, followed by restoration through ditch blocking. In the laboratory we measured horizontal (K h ) and vertical (K v ) hydraulic conductivity. We fitted linear multiple regression models to describe log 10 -transformed K h and K v on the basis of simple, easy-to-measure predictors. Dry bulk density and degree of decomposition were the strongest predictors of K h and K v . Perhaps surprisingly, the independent effect of hummocks was to produce higher-K v peat than in lawns; while the independent effect of restored diggings was to produce higher-K peat than in uncut locations. Our models offer high explanatory power for K h (adjusted r 2 = 0.740) and K v (adjusted r 2 = 0.787). Our findings indicate that generalizable predictive models of peat K, similar to pedotransfer functions for mineral soils, may be attainable. K h and K v possess subtly different controls that are consistent with the contrasting roles of these two properties in peatland water budgets. Our near-surface samples show no evidence for the low-K marginal peat previously observed in deeper layers at the same site, indicating that such structures may be less important than previously believed.

Increasing dominance by purple moor grass, Molinia caerulea (‘Molinia’) on globally rare and protected blanket bogs of the United Kingdom and the South Pennines is a growing threat to diversity and carbon storage, as well as increasing the risk of wildfire. In a trial to increase diversity using Sphagnum plugs planted on three Molinia‐dominated sites in the South Pennines, an initial rapid increase in cover of plug‐derived Sphagnum (PDS) suggested an advantage over that of naturally occurring Sphagnum colonies, the latter remaining below 1% cover throughout; subsequent plateauing of PDS cover in areas of moderate Molinia cover (<80%) was linked with drought stress, whereas declining cover in Molinia‐dense areas (>80%) suggested additional competition for light. The cover of Molinia was only weakly reduced by, and then completely recovered from, a baseline flailing treatment. Increasing cover of PDS in all of the treatments had no clear effect on the cover of Molinia. The cover of naturally occurring indicator species was strongly reduced by the baseline flailing treatment; subsequent recovery was not complete, even with contributions by PDS. There was a negative linear relationship between Molinia cover and indicator species cover, over all ranges of Molinia cover. Water table depths were lowered by PDS during the first 3 years of the trial, perhaps due to facilitated capillary conduction of water through the buried plug tissues. It was concluded that PDS can establish rapidly amongst Molinia, boosting the diversity and cover of indicator species, but that establishment is slower in areas of dense Molinia and also likely to be hampered by periods of severe drought stress. Prior flailing had no clear benefit on the growth of PDS but reduced the cover of naturally occurring indicator species. Further investigations should include the role of water stress, shading and phosphorus limitation in restricting the growth of PDS within Molinia‐dominated swards.

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