Gap closure: use of Magic model to predict time required to achieve steady-state following implementation of the Oslo protocol
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- NIVA-rapport 
Reduction of sulphur deposition causes recovery of acidified surface waters. Processes in the catchment delay recovery. The acidification model MAGIC was applied to the Vikedal and Tovdal rivers in southern Norway. Water response is delayed by about 10 years at both rivers delay is due to release of old sulphate at Vikedal, and cation exchange at Tovdal. Assuming that the Oslo protocol is fully implemented by the year 2010, about 60% of the increase of ANC will occur in the next 13 years (1997-2010) with a new steady-state reached by about 2046. Liming requirement for both rivers will be reduced to about 90% of present-day levels by the year 2010 and to about 70% by the year 2046. One of the main purposes of the Norwegian national monitoring programme is to provide documentation of changes in environmental quality due to long-range transported air pollutants. Modelling applications such as this clearly show that the data fill this purpose.