Hydro-physical properties and 3D X-ray computed tomography pore architecture across natural, drained, and rewetted fen peat soils

Peatland drainage disrupts hydrological functioning, degrades peat soils, and accelerates carbon loss. Although rewetting is increasingly promoted to reverse these impacts, the extent to which it can restore peat structure and hydro-physical properties remains unclear. Here, we examined peat structure and hydro-physical properties along a sequence of fen peatland states—near-natural, drained, and rewetted since 1997. The hydro-physical properties including bulk density ( ρ b ), soil organic matter content (SOM), saturated hydraulic conductivity ( K s ), soil water retention curves (SWRCs), and drainable porosity ( ϕ d ) were measured using peat cores of 250 cm 3 . In parallel, undisturbed peat soil cores (10 cm in height) collected from the upper peat layer (0–15 cm depth) were analyzed using X-ray computed tomography (CT) to characterize CT-resolvable pore size and geometry. K s was additionally measured on the same CT-imaged cores, enabling direct linkage between pore-network architecture and K s . The results indicated that, relative to near-natural peat, rewetting only partially recovered ρ b and SOM, whereas macroporosity, K s , and SWRCs were fully recovered. A strong correlation was observed between ϕ d and log 10 K s ( R 2 ≥ 0.73, p < 0.001), indicating that this easily measurable property may serve as a practical predictor of K s in peat soils. CT-based analyses further showed that natural and rewetted peat soils had a greater mean macropore diameter of the limiting slice (MDLS; i.e., the CT slice with the lowest CT-resolvable air-filled porosity) and longer maximum macropore vertical extent (MVE) than drained peat. In contrast, the largest pore networks in drained peat lacked continuous pathways for water transmission at the CT-resolvable scale. In the 10-cm-high CT-imaged peat cores, three-dimensional pore-network metrics—particularly CT-resolvable air-filled porosity and MVE—explained more than 87% of the variability in K s . Overall, our findings demonstrate that long-term rewetting, with the water table maintained near the ground surface, can substantially restore functional soil structure and water transmission capacity in the topsoil of previously degraded fens, with re-established pore connectivity emerging as a key mechanism driving near-surface hydrological recovery.