Impacts of afforestation on groundwater resources and quality

Plans to double the proportion of land under forest cover in Ireland by the year 2035 have been initiated. The plan, primarily financially driven, ign ores potential environmental impacts of forestry, particularly impacts on g roundwater resources and quality. Since groundwater supplies almost 25% of Ireland's total potable water, these impacts are important. Field investiga tions indicate that afforestation leads to a reduction in runoff by as much as 20%, mainly due to interception of rainfall by forest canopies. Clearfe lling has the opposite impact. Implications are that uncoordinated forestry practices can potentially exacerbate flooding. Groundwater recharge is aff ected by forestry, largely due to greater uptake of soil water by trees and to increased waterholding capacity of forest soils, arising from higher or ganic contents. Recharge rates under forests can be reduced to one tenth th at under grass or heathland. Groundwater quality may be affected by enhance d acidification and nitrification under forests, due partly to scavenging o f atmospheric pollutants by forest canopies, and partly to greater depositi on of highly acid leaf litter. The slower recharge rates of groundwater und er forests lead to significant delays in manifestation of deterioration in groundwater quality.