title: Nitrogen deposition and exceedance of critical loads for nutrient nitrogen in Irish grasslands.
abstract: High resolution nitrogen (N) deposition maps were developed to assess the exceedance of empirical critical loads of nutrient N for grasslands in Ireland. Nitrogen emissions have remained relatively constant during the past 20 yrs and are projected to remain constant under current legislation. Total N deposition (estimated as wet nitrate [NO3(-)] and ammonium [NH4(+)] plus dry NO× and NH3) ranged from 2 to 22 kg Nha(-1)yr(-1) (mean=12 kg Nha(-1)yr(-1)) to grasslands. Empirical critical loads for nutrient N were set at 15 kg Nha(-1)yr(-1) for both acid and calcareous grasslands; exceedance was observed for ~35% (~2,311 km(2)) of mapped acid grasslands. In contrast, only ~9% of calcareous grasslands (~35 km(2)) received N deposition in excess of the critical load. Reduced N deposition (primarily dry NH3) represented the dominant form to grasslands (range 55-90%) owing to significant emissions associated with livestock (primarily cattle). The extent of exceedance in acid grasslands suggests that N deposition to this habitat type may lead to adverse impacts such as a decline in plant species diversity and soil acidification. Further, given that elevated N deposition was dominated by NH3 associated with agricultural emissions rather than long-range transboundary sources, future improvements in air quality need to be driven by national policies.
authors.affiliation: Trent University, 1600 West Bank Drive, Peterborough, Ontario K9J 7B8, Canada. Electronic address: jasonhenry@trentu.ca.
authors.forename: Jason
authors.initials: J
authors.lastname: Henry
authors.affiliation: Trent University, 1600 West Bank Drive, Peterborough, Ontario K9J 7B8, Canada.
authors.forename: Julian
authors.initials: J
authors.lastname: Aherne
mesh_terms: D000383:Agriculture; D000818:Animals; D002417:Cattle; D004784:Environmental Monitoring; D007494:Ireland; D009584:Nitrogen / Q000032:analysis*; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D009584:Nitrogen
keywords: Acid and calcareous grasslands; Ammonia; Biodiversity; Critical load; Exceedance; Nitrogen deposition