Nitrogen deposition and exceedance of critical loads for nutrient nitrogen in Irish grasslands

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• 作者：Jason Henry ; Julian Aherne
• 关键词：Nitrogen deposition ; Ammonia ; Biodiversity ; Acid and calcareous grasslands ; Critical load ; Exceedance
• 刊名：Science of the Total Environment
• 出版年：1 February, 2014
• 年：2014
• 卷：470-471
• 期：Complete
• 页码：216-223
• 全文大小：986 K

文摘

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^{鈭?/sup>] and ammonium [NH₄+] plus dry NO_脳 and NH₃) ranged from 2 to 22 kg N ha鈭?#xA0;1 yr鈭?#xA0;1 (mean = 12 kg N ha鈭?#xA0;1 yr鈭?#xA0;1) to grasslands. Empirical critical loads for nutrient N were set at 15 kg N ha鈭?#xA0;1 yr鈭?#xA0;1 for both acid and calcareous grasslands; exceedance was observed for ~ 35% (~ 2311 km2) of mapped acid grasslands. In contrast, only ~ 9% of calcareous grasslands (~ 35 km2) 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.}