Calculation and mapping of critical loads of sulfur and nitrogen in Flanders, Belgium

Up to now, critical loads calculations for the Flemish Region were based on European background data of surrounding countries. A first attempt has been made to calculate and map critical loads for forest ecosystems in Flanders using available site-specific information. Values of current deposition were used to calculate and map exceedances. The lowest critical loads for acidification (697 eq ha(-1)year(-1)) occur in the Campine and the north of Limburg where ecosystems largely consist of coniferous forests on poor sandy soils. The dominance of coniferous forest types in the Campine is also responsible for low critical load values for eutrophication (between 536 and 971 eq ha(-1)year(-1)). In 75% of the receptor points that have been considered an exceedance of the critical load for acidification is noted, primarily in areas with high SO2 and NOx depositions, such as the north of the provinces East and West Flanders and Antwerp. The critical load for eutrophication is exceeded in all points considered. Exceedances are particularly high in coniferous forests in West Flanders, and in the north of the provinces of Antwerp and Limburg, where especially NHx depositions amount to high values. Data needed for the calculation of critical loads are still sparse in Flanders, e.g. for: (1) weathering rates of soil minerals; (2) interception and evaporation of forest ecosystems; and (3) uptake of N and basic cations by vegetation. This supplementary information will contribute to a further refining of the calculated critical loads, which constitute indispensable information in developing an emission abatement policy.