Critical limits for surface water acidification in Norwegian critical loads calculation and Water Framework Directive classification

Summary

The objective of this study was to compare the critical limits for surface water acidification used in the critical loads calculation under the UNECE Convention on Long-range Transboundary Air Pollution and the EU Water Framework Directive (WFD) classification in Norway. The critical limits to be compared were the ANClimit,oaa,var from the critical loads calculation and the ANC good-moderate boundary values from the WFD classification. They are not directly comparable, but were compared by using them to calculate critical loads. ANC good-moderate boundary values from the first WFD classification manual gave unrealistic results, showing that these boundary values were too high. Critical loads based on the ANClimit,oaa,var from the critical loads work and the ANC good-moderate boundary values from the second WFD classification manual gave fairly harmonised results. Thus, the requirements set by the two management systems are similar. However, the WFD requirements are somewhat less strict overall, and especially for regions with naturally low buffering capacity or high TOC concentration. Splitting the upper TOC category is recommended. Further harmonisation of the critical limits is possible, but the WFD concept of discrete boundary values sets limitations to complete harmonisation. Updating the ANClimit,oaa,var based on changes in TOC concentration could be considered.