Long term effects on water streams of wood ash recycling to a forest plantation

The chemical composition of runoff from a wood ash fertilized catchment in central Sweden have been studied during eight years after the treatment. The effects of the ash treatment was compared with a 12ayear long reference period and a reference catchment close to the ash treated catchment. The ash treated area was earlier (winter 1980/81) whole-tree-harvested to 90 %. At the same time the reference area was stemwood harvested on 60 % of the area. Both areas were planted with spruce and pine. Granulated ash was spread on the whole-tree-harvested area, by helicopter, on two occasions (1aton per hectare in May 1989 and 2 tonnes per hectare in October 1991). During the first ash application a marked peak in K concentration was observed. The second ash application caused a high peak in K concentration. Short-lived peaks was also observed for pH, electric conductivity, ANC, Mg, Na and Cl. Significant increases of pH, electric conductivity, Ca, K and Cl was observed in runoff water from the ash treated area during the 8-year-period after the last ash spreading. However, during the same period concentrations of NH4-N, N03-N and total N have shown a relative decrease in runoff water from the ash treated area, compared to the reference area.