An assessment of the acidifying effects of afforestation in acid-sensitive catchments in County Wicklow

Abstract

This investigation aimed to determine the extent of forestry-induced acidification of salmonid rivers and streams in acid sensitive catchments of County Wicklow. The study involved a detailed chemical examination of four selected acid sensitive catchments from January to May 2004, viz. Vartry Reservoir Inflows, Cloghoge River, Glendalough Lake Upper and the King’s River. Sampling sites varied as to the characteristics of their catchment, e.g. afforested, partially afforested, moorland and areas harvested of trees, allowing for comparisons of chemical data. It was demonstrated that streams draining afforested catchments were artificially acidified compared to non-forested streams. Statistical analysis rejected the null hypothesis (ANOVA: F > F Critical, T-Test: t stat > t Critical) that there was no significant difference in surface water chemical quality between afforested and moorland sampling sites and afforested and clearfelled sites. There were highly significant differences between afforested and moorland sites for pH, alkalinity, total aluminium, colour, TON, chloride and calcium at all catchments. Streams draining heavily afforested catchments were shown to experience greater acid episodes compared to partially or non-forested streams. The data presented in this report furthers our understanding of acidification due to afforestation in Ireland and coupled with past and present research, should assist in a review of the Forestry and Water Quality Guidelines, especially with regard to designation of acid-sensitivity and remediation measures.