Boreal Peatland LIFE -project – Effect of restoration and drainage on peatland hydrology – A study of data before and after restoration at 46 sites in Finland

Peatland restorations have been actively done in Finland since the 1970s. The restoration has covered about 1300 hectares of land annually in order to meet the global target of halting the loss of biodiversity and secure ecosystem services. This is for the fact that restoration of drained peatlands is believed to restore back the lost biodiversity or cutoff the loss and naturalize degraded ecosystems. Hence, in this study a total of 46 boreal peatland were investigated, of which 20 are fens, 13 pine mires and 13 spruce mires, with peatland types ranging from nearly ombrotrophic Sphagnum bogs to rich fens. The 27 study sites were drained/restored state and the rest 19 sites were in pristine condition. The pore water chemistry and continuous water table data at all study sites, runoff and stream water chemistry at nine study sites have been monitored since 2008 and are analyzed in this report.

According to our study, drainage has lowered the groundwater level (WT) of mires statistically significantly and also changed the fluctuation dynamics of the WT. Restoration measures have successfully raised the WT to a more natural level (equivalent to the pristine groundwater level) as proven by statistical tests and also restored the natural fluctuation dynamics of the groundwater level. There were differences in the WT rise between mire types. In general, the mean groundwater level rise in nutrient poor spruce mires were larger than the rest of the peatland types considered in this study.

Our study shows also that peatland drainage has changed the chemical properties of pore water as the concentrations of DOC, Ptot and Ntot were considerably higher in the pore water of the drained sites than in the pristine sites in most cases. According to our study, restoration improved the quality of pore water in most of the mire types and with respect to most of the monitored variables. This positive effect was especially evident and statistically significant for DOC and Ntot but concentrations of Ptot also showed notable reductions after restoration, suggesting that after restoration pore water quality is getting closer to natural. Generally pH as a water quality parameter and Eutrophic fens were different in this respect: pH was lowered in all mire types and Eutrophic fens showed slight increase in concentrations of DOC, Ptot and Ntot after restoration.

The chemical quality of pore water and the water flowing from the mires to recipient water courses was compared statistically and gave strongly correlated results, implying that monitoring of pore water quality can be used to estimate the effect of peatland restoration on water quality at receiving water bodies.

Overall, restoration was proven to be an effective tool in restoring the hydrology of mires and subsequently helps bring back the natural ecosystem function (e.g. accumulation of peat) and structure (e.g. mire species) but the monitoring should be continued to get reliable results of the long-term effects of peatland restoration on water quality in the downstream watercourses.