Long-term changes in the pore and runoff water quality in restored boreal peatlands

In Finland over half of the mire habitat types are endangered mainly due to drainage-induced succession towards more forested type ecosystems. Restoration is thought to be an important tool to improve the status of degraded peatlands. National and European Union level strategies to improve nature conservation have a target of increasing the allocation of restoration actions to peatlands in Finland. Thus, the effects of peatland restoration need to be understood.

Peatland drainage lowers the water table and exposes peat to decomposition. Restoration aims to raise the water table, but it simultaneously causes a new disturbance to surface layers often resulting in elevated nutrient and organic carbon concentrations in pore and runoff waters. Typically, the water quality disturbance starts to dampen out in the subsequent years after restoration. The rate and disturbance level depend on e.g., the actual measures, peatland type, and trophic level. To minimize and avoid impacts as well as to find the best restoration practices, knowledge of the long-term (over 10 years) effects of restoration measures is needed.

The hydrology of drained and restored peatlands and pristine counterpart mires have now been monitored for almost 15 years in the Parks and Wildlife Finland’s (Metsähallitus) peatland monitoring network. The data consists of high-frequency water table data and pore water quality measurements (four times per growing season) from 46 sites all over Finland with varying nutrient levels and openness (as one of the key indicators for peatland type). Additionally, ten sites have been tested for surface peat quality. Runoff water quality and quantity have been monitored in three of the pristine and five drained and restored sites. In this study, we report the long-term effects of peatland restoration on the water table and water quality in different peatland types. We also focus on understanding the connection of water quality variation in pore and runoff waters, intending to simplify the practical evaluation of peatland restoration success.