Assessment of the Potential Impacts of Reactive Nitrogen Deposition on Irish Semi-Natural Grassland Habitat

Elevated chronic atmospheric emission of nitrogen (N) has prompted studies world-wide to assess the impacts of N deposition on terrestrial ecosystems. In this study, the spatial extent and magnitude of empirical critical load exceedance was evaluated for reactive N (Nr) deposition in semi-natural grassland habitats. Empirical critical load exceedance was predicted for ∼75 % of dry and ∼32 % of wet acid grassland habitat. In contrast, only ∼8 % of dry and ∼16 % of wet calcareous grassland habitat exceeded the critical load for Nr. A gradient study was also carried out using plant releve data to determine if N deposition was related to biodiversity in semi-natural grassland habitats. A significant negative relationship between N deposition and plant species diversity was determined for acid and neutral-calcareous grasslands. However, multiple regression analysis indicated that site specific variables such as topsoil pH, graminoid and herb height and litter cover were the primary predictors of plant species diversity.;Keywords: nitrogen deposition, semi-natural grasslands, biodiversity, eutrophication, soil nitrogen, critical load, exceedance.