The effect of clearfelling a Sitka spruce ( Picea sitchensis) plantation on solute concentrations in drainage water

Abstract

Water samples were collected from the drainage system of a Sitka spruce plantation at weekly intervals for six years. The drainage system had been designed to divide the plantation into a series of artificial catchments, three of which were designated experimental plots and clearfelled in the second year of sampling while a fourth was the control plot which remained unfelled until the end of the study. Prior to felling, solute concentrations were similar for all plots. Concentrations of nitrate, potassium and phosphate all rose following felling. Nitrate concentrations peaked one year after the end of felling and returned to levels similar to the control plot in the fourth year after felling. Potassium and phosphate peaked in the second year after felling but had not returned to control levels by the end of the study, although seasonal patterns had become established, with lower concentrations in summer. Concentrations of sulphate, sodium and chloride declined as a result of felling and remained lower than the control at the end of the study. There was a very slight fall of pH and aluminium concentration after felling, relative to the control. The three experimental plots behaved in a similar way for all ions except phosphate and iron which were released in greatest quantities from the least intensively drained plot.