Assessing the effects of forest-to-bog restoration in the hyporheic zone at known Atlantic salmon (Salmo salar) spawning sites

Abstract

In the UK, large areas of blanket bogs were afforested with non-native conifers between the 1960s and the 1980s. Following recognition of the detrimental effects of such practice on biodiversity and carbon stocks, large-scale restoration trials started in the late 1990s and are further supported by recent changes in policy. The removal of forestry from peatlands is likely to be a widespread land-use change in the coming decades and could affect adjacent freshwater systems. This study aimed to investigate whether forestry removal with drain blocking affected nearby spawning sites used by Atlantic salmon (Salmo salar). We analysed the chemistry of hyporheic (beneath and just above the streambed) and surface water, and measured sediment deposition upstream of, within and downstream of a forestry block in the north of Scotland, during and after restoration management operations. We found no immediate effect of management except on potassium and zinc concentrations, which increased after restoration. The general lack of effect is attributed to catchment properties, including the small proportion of catchment (< 5 %) affected by management, and to dilution effects related to heavy precipitation during the intervention phase. We suggest that longer-term monitoring should be implemented as the sizes of areas undergoing restoration management increases.