Unveiling water table tipping points in peatland ecosystems: Implications for ecological restoration

• Fen shows more consistent patterns of responses to WTD changes than bogs. • Environmental factors and peatland characteristics limit the WTD effect. • WTD tipping points for all the mechanisms in peatlands are not established yet. • The threshold of fens is placed at a higher WTD (−15 cm) than bogs (−20 cm). • The higher amount of nutrients in fens induces a more direct link with WTD. Peatlands play a significant role in the global carbon cycle as an essential organic carbon sink. However, a concerning trend reveals that more than 15 % of peatlands worldwide have been drained; this hydrological problem is expected to deepen with the ongoing global warming. The appropriate management of the water table depth (WTD) emerges as an essential strategy in the protection of peatlands from drainage and degradation. These ecosystems are also under the influence of seasonal hydrological changes, which exert profound effects. A low water table facilitates oxygen availability in the peat, leading to the decomposition of organic matter and significant shifts in vegetation. Conversely, high water table levels encourage anaerobic conditions, fostering peat accumulation while suppressing microbial activity. Extreme climate events or human interventions further trigger water table fluctuations, potentially pushing peatlands beyond recovery thresholds and leading to irreversible degradation. Therefore, this comprehensive review and meta -analysis explores the responses of peatlands to water table fluctuations. We tried to identify critical tipping points driving vegetation succession, nutrient cycling, acidity levels, and exoenzymatic activities. The study found out deeper levels of WTD are needed to trigger the chain of effects in peatland balance for bogs (from –31 cm to –23 cm) than for fens (from –14 cm to –12 cm)( and that some changes are only directly related with WTD in undisturbed peatlands (e.g. changes in acidity, less stable vegetation succession). Recognising these critical thresholds is of utmost importance, as it holds the key to preventing further degradation of invaluable peatland ecosystems and appropriate restoration methods.