LONG-TERM DISSOLUTION OF SEDIMENTED LIMESTONE POWDER IN RUNNING WATER. CONSEQUENCES FOR LIMING STRATEGY AND INTERPRETATION OF LIMING EFFICIENCY DATA
Liming of Fosstølbekken, a brook in Aust-Agder county, southern Norway, was stopped during two flow episodes in order to study long-term dissolution of sedimented limestone powder. The pH increasing capacity was adequate over a certain period of time. This capacity was considerably reduced during the second flow episode, where pH only increased from 4.8 to 5.5 at peak flow. Liming strategy may take into consideration significant long-term dissolution when pH governed lime dosing is included. It is anticipated that this should increase the cost-efficiency of liming in running water. The pH registration site should be situated several hundred meters downstream the lime doser. Long-term dissolution of previously sedimented lime is an important factor for interpretations of liming efficiency data. Dissolved calcium concentrations may be overestimated by a varying amount originating from long-term dissolution.