The Global Nitrogen Cycle; Emissions, Transformations and Deposition of Reactive Nitrogen and Effects on Terrestrial Ecosystems in the 21st Century
Abstract:Human impacts on the Global cycling of fixed nitrogen and likely trends through the 21stcentury
Of the ~400Tg-N of reactive nitrogen fixed globally each year approximately half results directly from human activity. The chemical form and concentration vary spatially and temporally, with pronounced hot spots due to industrial, transport and agricultural activities resulting in local, regional and global effects on climate, ecosystems and human health. Nitrogen compounds are unusual in being implicated in most of the current regional and global environmental concerns including, climate change, air quality and biodiversity loss, yet in none of the issues is nitrogen the most important contributor. Thus the very widespread effects of reactive nitrogen in the environment are not widely recognised and are little known to the wider public. This paper presents an update of current understanding of the global nitrogen cycle and the likely effects of changes in climate and agriculture on the N cycle this century.