Water chemistry following wood-ash application to a Scots pine stand on a drained peatland in Sweden

The availability of phosphorus and potassium often limit growth of trees on well drained peatlands in the boreal region. Wood ash, which contains phosphorus and potassium, can be used for forest fertilization on peatlands or for nutrient compensation following intensive harvesting. This study was performed in order to investigate the effects on water chemistry of applying wood ash to a Pinus sylvestris L. stand on a drained peatland in southern Sweden. Runoff chemistry was monitored in the main ditch for one year before and three years after the application of self-hardened and crushed wood ash, applied at an average rate of 3.1×10³ kg per hectare. In addition, groundwater was collected from the ash-treated peatland and from an adjacent reference peatland and chemically analysed. Shortly after woodash application, the concentrations of boron, calcium, potassium, lithium, magnesium, manganese and sulphate in the ditch water, and the electrical conductivity, all increased. Some variables showed elevated concentrations for a few months only, while pH and the concentrations of boron, potassium, lithium, magnesium, manganese, total phosphorus and silica were significantly (p < 0.05) elevated over the last one and a half or two years of the study, compared to the reference period. The concentrations of iron, total sulphur and sulphate were lower during the last one and a half or two study years than in the reference period. Several trace metals and anions did not appear to be affected. In general, the effects detected in groundwater were consistent with those found in ditch water. Groundwater flow through superficial soil layers seems to have facilitated leaching