The effect of compression on Sphagnum hydrophysical properties: Implications for increasing hydrological connectivity in restored cutover peatlands

Sphagnum moss, a dominant peat‐forming species in northern peatlands, relies on capillary rise to sustain metabolic activities. However, in restored peatlands, a capillary barrier resulting from distinctly different pore‐size distributions in the degraded remnant cutover peat and regenerated Sphagnum moss limits capillary rise. Space‐for‐time analogues suggest it could take >40 years for decomposition and degradation of the moss profile to overcome this capillary barrier effect. This paper explores the feasibility of mechanical compression to ameliorate the capillary barrier effect and accelerate the return of ecohydrological function in restored Sphagnum moss. Seven reference cores (10 × 20 cm) and 29 samples (10 × 5 cm) representing various depths from surface (0–5 cm, n = 9; 5–10 cm, n = 9; 10–15 cm, n = 7; 15–20 cm, n = 4) were tested in a laboratory setting to analyse pre‐compression and post‐compression water retention‐unsaturated hydraulic conductivity relationships, proportion of macropores, and other hydrophysical parameters. Post‐compression, reference core moss height (originally 20 cm) decreased by 5.5 ± 1.2 cm, and sample bulk density increased, while porosity decreased (Wilcoxon signed rank test, p 75 μm). Simulation results with Hydrus‐1D indicate that the post‐compression moss profile was better suited to maintain pressure heads above critical values for photosynthesis. These findings suggest that mechanical compression may be used to ameliorate the capillary barrier effect in restored cutover peatlands; however, field scale studies are required.