title: Consequences of human modification of the global nitrogen cycle.
abstract: The demand for more food is increasing fertilizer and land use, and the demand for more energy is increasing fossil fuel combustion, leading to enhanced losses of reactive nitrogen (Nr) to the environment. Many thresholds for human and ecosystem health have been exceeded owing to Nr pollution, including those for drinking water (nitrates), air quality (smog, particulate matter, ground-level ozone), freshwater eutrophication, biodiversity loss, stratospheric ozone depletion, climate change and coastal ecosystems (dead zones). Each of these environmental effects can be magnified by the 'nitrogen cascade': a single atom of Nr can trigger a cascade of negative environmental impacts in sequence. Here, we provide an overview of the impact of Nr on the environment and human health, including an assessment of the magnitude of different environmental problems, and the relative importance of Nr as a contributor to each problem. In some cases, Nr loss to the environment is the key driver of effects (e.g. terrestrial and coastal eutrophication, nitrous oxide emissions), whereas in some other situations nitrogen represents a key contributor exacerbating a wider problem (e.g. freshwater pollution, biodiversity loss). In this way, the central role of nitrogen can remain hidden, even though it actually underpins many trans-boundary pollution problems.
authors.affiliation: Louis Bolk Institute, Hoofdstraat 24, 3972 LA Driebergen, The Netherlands. j.erisman@louisbolk.nl
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Erisman
authors.forename: James N
authors.initials: JN
authors.lastname: Galloway
authors.forename: Sybil
authors.initials: S
authors.lastname: Seitzinger
authors.forename: Albert
authors.initials: A
authors.lastname: Bleeker
authors.forename: Nancy B
authors.initials: NB
authors.lastname: Dise
authors.forename: A M Roxana
authors.initials: AM
authors.lastname: Petrescu
authors.forename: Allison M
authors.initials: AM
authors.lastname: Leach
authors.forename: Wim
authors.initials: W
authors.lastname: de Vries
mesh_terms: D044822:Biodiversity; D057231:Climate Change; D017753:Ecosystem; D004785:Environmental Pollutants / Q000009:adverse effects* / Q000032:analysis*; D005523:Food Supply / Q000592:standards; D005579:Fossil Fuels / Q000032:analysis; D006802:Human Activities; D006801:Humans; D058458:Nitrogen Cycle
chemical_list: D004785:Environmental Pollutants; D005579:Fossil Fuels
keywords: biodiversity; climate; environmental effects; food security; human health; reactive nitrogen