Critical Loads for Nitrogen Based on Criteria for Biodiversity Conservation

The increased focus on biodiversity following inter alia the 1993 Convention on Biological Diversity and the EU Nature Directives has led to a demand for the inclusion of biodiversity effects in the development of air pollution policies in Europe. This paper presents a method for the calculation of critical loads for nitrogen with biodiversity protection as end-point. The method has been used in a national assessment in Denmark based on national monitoring data. The method is based on the use of a coupled soil geochemical and plant occurrence model, VSD+/ MOVE, with Mean Species Abundance as indicator and "no net loss" of biodiversity compared to a given reference year as criterion. Calculated critical loads with 2010, 1992, and 1950, respectively, as reference years are on average 9.4, 8.5, and 6.8 kg N ha(-1) yr(-1), and thereby substantial lower than the median value of the empirical critical load ranges for the same habitat types.