Contrasting Energy And Water Balance Regimes Between A Rewetted Peatland And An Abandoned Peat Extraction Area In Estonia

Peatland restoration has emerged as a key climate mitigation strategy due to its potential to reduce greenhouse gas emissions and improve ecosystem functioning. Beyond carbon cycling, restoration fundamentally alters surface energy partitioning and hydrological processes by modifying vegetation structure, water table dynamics, and surface-atmosphere exchanges. However, the extent to which rewetted peatlands in abandoned peat extraction areas differ from drained systems in terms of coupled energy and water balance dynamics remains poorly quantified, particularly under similar climatic forcing. Understanding these differences is essential for assessing the broader climatic and ecohydrological implications of peatland restoration. In this study, we compared the surface energy balance, water balance, and hydroclimatic controls at two contrasting peatlands in Estonia: Lavassaare, an abandoned drained peat extraction area, and Ess-soo, a recently rewetted site. Half-hourly radiation and turbulent flux measurements from 2024 were used to derive net radiation (Rn), sensible (H) and latent heat fluxes (LE), ground heat flux (G), evapotranspiration (ET), and potential evapotranspiration (PET). Monthly energy balance components exhibited strong seasonality at both sites, with LE dominating during the summer, while H increased during transitional dry periods. Annual ET totals were comparable between sites (449 mm at Ess-soo vs. 455 mm at Lavassaare), despite higher annual precipitation at Ess-soo (630 mm compared to 563 mm). As a result, Ess-soo exhibited a larger annual water surplus (P-ET = +181 mm), whereas Lavassaare operated closer to zero balance during the growing season. Hydroclimatic indices further revealed distinct functional regimes. Lavassaare showed consistently higher monthly dryness ratios (ET/P), reaching values near or above 1 during late spring, indicating temporary water limitation. In contrast, Ess-soo maintained lower ET/P values and a stronger water surplus throughout the year. Budyko analysis confirmed these patterns: Ess-soo occupied a more water-limited position (Φ = PET/P = 2.78; EI = ET/P = 0.71), whereas Lavassaare (Φ = 1.71; EI = 0.81) was closer to the energy-limited region of Budyko space. Together, these results demonstrate that the rewetted Ess-soo peatland maintains higher hydrological buffering capacity, while the abandoned Lavassaare site experiences stronger atmospheric demand relative to available water. The combined energy-water framework highlights the sensitivity of peatland surface-atmosphere exchanges to restoration status and provides a basis for understanding future ecosystem responses under changing climatic conditions.