Abstract:Butterfly decline in Northern Europe is a cause of concern and it has been hypothesised that this is due to nitrogen deposition inducing excess early growth of plants. It has also been changing the quality of the food available to larvae. We tested these hypotheses by linking butterfly biodiversity quality indices (species richness, population, biomass, conservation value, evenness (Simpson's Index) and modelled species richness (Chao 1 and 2)) with Nitrogen Critical Load Exceedence (nCLE) data. An index of butterfly sensitivity to nitrogen was also created (SpeciesThe results included multiple biodiversity quality indices based on 17 years of data (aggregated into three periods of six, six and five years to give 287 datasets) in four habitat types (grassland, heathland, woodland and farmland) were tested for linkages using Principle Component Analysis. This analysis showed that all indices, including nitrogen deposition, were in decline, with the exception of SNVI.Analysis conducted on all four habitats showed that nitrogen deposition was in decline, except for heathland where the last 11 years did not show any significant decline. Heathland also showed an anomalous biodiversity quality profile for these last 11 years. It is suggested that the sensitivity of heathland to nitrogen deposition means that it will require considerable further efforts to achieve a nitrogen deposition that is not excessive.Restoration of all sites will take time due to the multiple hindrances to colonization, which in the case of heathland might prevent successful colonization for the foreseeable future. These results indicate the efficacy of butterfly biodiversity quality and nCLE as an indicators for the SEBI 2020 process (Streamlining European Biodiversity Indicators) by showing the relationship between them.