Hydrological Response to Rewetting of Drained Peatlands – a Case Study of Three Raised Bogs in Norway

Proper peatland functioning depends on a suitable water level, and this is also a prerequisite for the provision of ecosystem services beyond water retention. The majority of degraded peatlands have been drained for agriculture and forestry through the construction of ditches, and the most common initial step in restoration-oriented management of drained peatlands is rewetting through ditch-blocking. This field-monitoring-based study aimed to analyze the hydrological response of three independent drained raised bogs in Norway (Aurstadmåsan, Midtfjellmåsan, and Kaldvassmyra) to ditch-blocking. The hydrological response to rewetting, as well as drain-blocking efficiency, was assessed based on groundwater level monitoring conducted from 2015 to 2021, following a Before-After-Control-Impact (BACI) design. Data were collected from water level loggers installed in piezometers at various locations in each site. At each site, an increase in average groundwater level was observed after rewetting. In both Aurstadmåsan and Midtfjellmåsan, most piezometers documented an increase in average groundwater level after rewetting. In Kaldvassmyra, 3 out of 8 piezometers showed an increase in average groundwater level. Considering data from all impact piezometers, groundwater level increased by an average of 6 cm, while the same value for control piezometers was -2 cm. The area influenced by rewetting due to ditch-blocking was 12.7-24.8 m from the ditch, with an average of 17.2 m. Additionally, rewetting increased the duration of groundwater levels favorable for peatland functioning by 27.7% on average, using the water table depth critical for plant communities as a reference. It is expected that both the area impacted by rewetting as well as the groundwater level rise will increase over time. The results suggest that ditch-blocking is an effective tool in restoring the hydrological conditions of peatlands, although its efficiency is limited spatially and may be affected by meteorological factors. An evaluation of restoration success should be complemented by analyses of the impact on vegetation and greenhouse gas emissions.