Effects of Drainage and Subsequent Restoration on Peatland Hydrological Processes at Catchment Scale

Potential benefits of peatland restoration by rewetting include carbon sequestration, restored biodiversity, and improved hydrological functions. There is great uncertainty about how catchment hydrological processes change after restoration, with a particular lack of well-documented catchment runoff data. This study compared five formerly Disturbed (now Restored) and two undisturbed peatlands. In total, 455 and 728 hydrological events were selected for the analysis, using a three-event selection technique. Mean event runoff coefficient (RC) values varied greatly between conditions and hydrological events. RC in Disturbed conditions was slightly higher than in undisturbed conditions, but RC in Restored conditions was higher than under other conditions. Mean transit time revealed that event rainfall water reached the outlet faster in Disturbed conditions. Mean event peak flow in Disturbed conditions was higher and peaked faster than under other conditions. However, the base flow showed no noticeable difference between treatments. Significantly higher watertable (WT) rise per rainfall input (0.36-0.85 cm/mm) was observed in Disturbed conditions, due to lower specific yield (Sy) values (0.13-0.24) than under Restored and undisturbed conditions (Sy 0.25-0.50). Shallow WT showed significant positive correlations with runoff and storage properties and was a key component of the runoff generation mechanisms in peatlands. Storage-related parameters (Sy, WT rise per rainfall input) and catchment response time parameters revealed disturbance-related hydrological changes in peatlands more clearly than other runoff parameters tested (e.g., RC). Overall, with restoration, WT and storage properties recovered to the levels at undisturbed sites but increased runoff was observed occasionally due to wetter antecedent moisture conditions.