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Understanding the anthropogenic and natural factors that affect runoff water quality is essential for proper planning of water protection and forest management, particularly in the changing climate. We measured water quality and runoff from 10 unmanaged and 20 managed forested headwater catchments (7–12,149 ha) located in Finland. We used linear mixed effect models to test whether the differences in total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) export and concentrations observed can be explained by catchment characteristics, land use, forest management, soil fertility, tree volume and hydrometeorological variables. Results show that much of variation in TOC, TN and TP concentrations and export was explained by drainage, temperature sum, peatland percentage and the proportion of arable area in the catchment. These models explained 45–63% of variation in concentrations and exports. Mean annual TOC export in unmanaged catchments was 56.4 ± 9.6 kg ha−1 a−1, while in managed it was 79.3 ± 3.3 kg ha−1 a−1. Same values for TN export were 1.43 ± 0.2 kg ha−1 a−1 and 2.31 ± 0.2 kg ha−1 a−1, while TP export was 0.053 ± 0.009 kg ha−1 a−1 and 0.095 ± 0.008 kg ha−1 a−1 for unmanaged and managed, respectively. Corresponding values for concentrations were: TOC 17.7 ± 2.1 mg L−1 and 28.7 ± 1.6 mg L−1, for TN 420 ± 45 µg L−1 and 825 ± 51 µg L−1 and TP 15.3 ± 2.3 µg L−1 and 35.6 ± 3.3 µg L−1. Overall concentrations and exports were significantly higher in managed than in unmanaged catchments. Long term temperature sum had an increasing effect on all concentrations and exports, indicating that climate warming may set new challenges to controlling nutrient loads from catchment areas.

Ditch network maintenance promotes forest growth in drained peatland forests but increases nutrient and sediment loads, which are detrimental to water quality. Society needs to balance the harvest revenue from improved forest growth against deteriorating water quality. We examine socially optimal even-aged forest management in drained peatlands when harvesting and ditch network maintenance cause nutrient and sediment loading. The means to reduce loading include establishing overland flow fields and abstaining from ditch network maintenance. We characterize this choice analytically in a rotation framework and examine, in a numerical model, the key factors affecting the choice of forest management and water protection measures. We choose a drained peatland forest site located in northeastern Finland in the vicinity of ecologically vulnerable forest headwater streams. On the given drained forest site, we find a set of parameters under which implementing ditch network maintenance is privately but not socially optimal.

Environmental and economic performance of forestry on drained peatlands was reviewed to consider whether continuous cover forestry (CCF) could be a feasible alternative to even-aged management (EM). CCF was regarded feasible particularly because continuously maintaining a tree stand with significant transpiration and interception capacity would decrease the need for ditch network maintenance. Managing CCF forests in such a way that the ground water levels are lower than in clear-cut EM forests but higher than in mature EM forests could decrease greenhouse gas emissions and negative water quality impacts caused both by anoxic redox reactions and oxidation and mineralization of deep peat layers. Regeneration studies indicated potential for satisfactory natural regeneration under CCF on drained peatlands. An economic advantage in CCF over EM is that fewer investments are needed to establish the forest stand and sustain its growth. Thus, even if the growth of trees in CCF forests were lower than in EM forests, CCF could at least in some peatland sites turn out to be a more profitable forest management regime. An advantage of CCF from the viewpoint of socially optimal forest management is that it plausibly reduces the negative externalities of management compared to EM. We propose that future research in drained peatland forests should focus on assessing the economic and environmental feasibility of CCF.

Calibration-period/control-area approach was used to study nitrogen and phosphorus export from drained and productive Norway-spruce-dominated peatland forests following conventional stem-only and whole-tree harvesting. The study indicated high nitrogen and particulate phosphorus exports and lack of significant differences between the harvest treatments during the first 3-4 years after harvesting. The high extra nitrogen exports, increasing to a maximum level of about 10 kg ha(-1) during the third year after harvesting, were partly caused by the higher nitrate export than in previous studies. The study has a practical outcome that management of harvest residues (i.e. left on site or harvested) may not be an efficient means of mitigation of nitrogen and phosphorus exports. The high exports following harvesting underline the importance of using the best available water protection methods, such as sufficiently large wetland buffer areas, to decrease nutrient exports to watercourses from productive Norway spruce dominated peatland catchments.