Can water table and thermal regimes in boreal peatlands recover temporal dynamics in a decade after restoration?

Peatland restoration is increasingly implemented as a nature-based solution to recover ecosystem functions degraded by historical drainage, yet the temporal dynamics of hydrological and thermal recovery remain poorly understood, particularly at fine time scales. This study investigates the effects of restoration on water table (WT) and porewater temperature (T_pw) using high-resolution (30-min) data across 43 boreal peatlands in Finland, including drained, restored, and pristine sites, based on a long-term before-after control-impact experiment. Wavelet coherence analysis is applied to examine the temporal similarity between restored and pristine sites in terms of WT and T_pw dynamics across hourly to monthly scales.

Our results show that restoration significantly increases the global wavelet coherence of WT across all time scales, with the strongest recovery observed at daily and longer scales. However, WT coherence at sub-daily scales remains low, indicating incomplete recovery of short-term hydrological buffering. In contrast, T_pw dynamics show limited restoration effects, with significant coherence increases only at monthly scales. Differences in restoration response are evident among peatland types and trophic levels, with open mires and intermediate-nutrient sites exhibiting the highest post-restoration WT coherence. Temporal analysis reveals a gradual increase in WT coherence over the first six years post-restoration, followed by stabilization, while T_pw coherence remains variable. These findings highlight the importance of multi-scale temporal analysis in evaluating restoration success and underscore the need for long-term monitoring to capture the full trajectory of hydrological recovery in peatlands.