The effects of a pelletised limestone treatment on drainage water acidity within a forest catchment in mid-Wales

Three headwater source areas were identified within a strongly acidified forest catchment in the Llyn Brianne area of central Wales. Each received an aerial application of between 10 and 16 t ha^?1 of limestone pellets (composed of powdered chalk, starch and bentonite) in November 1988. The pH, calcium and aluminium levels within soil water and stream water were assessed at fortnightly intervals over a 3 year period to determine the impact of the treatment on drainage water acidity. The results demonstrated the importance of identifying the effective source areas within a catchment and treating these with a readily available form of powdered limestone. Treatment with a pelletised form was unsuccessful in eliminating periods of low pH and high aluminium concentrations within the headwaters of the forested catchment. This was attributed to the slow breakdown and dissolution of the limestone pellets under the forest canopy and the reduced importance of the surface runoff pathways owing to pre-afforestation cultivation and drainage, and soil drying by the forest crop.