Changes in Solute Chemistry of Drainage Waters Following the Clearfelling of a Sitka Spruce Plantation

Abstract

Water was collected weekly from the ditch systems of two plots, one draining standing forest, the other ground felled at 35 years of age. Before felling, the mean concentrations and annual export of ions were similar. In the first year after felling both water yield and the mean concentrations of potassium, nitrate, ammonium, phosphate and iron increased, compared with the standing forest, so that the export of these ions increased greatly. Except for ammonium, these levels were maintained in the second year after felling. Concentrations of those ions predominantly deposited from the atmosphere, sodium, sulphate and chloride, decreased relative to the control plot, although there was no reduction in amounts exported until the second year after felling. Concentrations of calcium and magnesium also decreased relative to the control plot but export increased, before falling in the second year after felling. Aluminium concentrations did not change but export increased in the first year following felling. Acidity (pH) of drainage water did not differ significantly between the plots in any year. In terms of drainage water quality, these data suggest that the impact of clearfelling on this site type is not great though it could temporarily increase the reported differences between coniferous forest and grassland.