The studies indicate that nutrient-poor (oligo-ombrotrophic) sites are often at risk of increased export of P after restoration, while on nutrient-rich sites there can be high release of any of the three elements (DOC, N, P) studied here. These impacts could at least initially be high enough to compromise the improvement in water purification processes, which is one of the expected positive outcomes of restoration of forestry-drained peatlands. In particular, the very high exports from some fertile sites (II) raise concern as these are among the most bio-diverse wetland ecosystems and thus encounter specific restoration need. Even though these restored swamps will later turn from sources to nutrient sinks, it will plausibly take a very long time before the sinks fully compensate for the nutrients initially released due to restora-tion measures, as well as before the receiving water courses fully recover from the impacts of restoration. Furthermore, as wetlands (both pristine and restored) rather produce DOC into water courses that retain it from surrounding mineral soil areas, it may be, because of initial release of DOC and no later retention, that the overall effect of restoration is increased DOC input into receiving water courses.
Whether there is a risk of very high P export seems to depend on whether the peat Fe and Al suffice to re-adsorb the released easily-soluble and redox-sensitive P. The risk of high exports of DOC and P could be connected to the fact that spruce swamps usually have large mineral soil up-slope catchments, which supply them with substantial water input after the ditches bordering the peatland and the mineral soil catchment are filled in. This in connection with the decomposed and poorly water-conducting surface peat could create a situation where the water level rapidly rises, perhaps to higher level than in an undrained state, and anoxic conditions form in the surface layers of the restored swamp. Besides increasing the release of water-borne nutrients and DOC, these pools may increase the emissions of CH4(IV).
Small brooks or other discharge channels are often present in spruce swamps in their pris-tine state. These are often straightened and deepened in connection with the drainage opera-tions and are treated as any other ditch in connection to the restoration operaopera-tions. It should be investigated whether these could instead of being completely filled in and/or dammed, be restored with less intensive measures. These measures could allow some surface flow to occur and the very surface peat layers to remain partly aerobic after restoration, such as they plausibly are in respective pristine swamps. This could also prevent the high CH4emissions observed in study IV.
Redox conditions in peat have not thus far been connectedin situto exports of nutrients or CH4emissions in drained peatland forests restoration status notwithstanding; neither have the conditions present in restored forestry-drained peatlands been compared to those present in undrained sites. This is a definite gap in the understanding of processes connected to water quality in restored sites. In addition, active mitigation measures such as two-staged restoration where a small portion of the catchment is first restored to provide a wetland buffer zone for the main restoration operations, should be investigated.
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