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Global Warming Implications of Anthropogenic Nitrogen Inputs to the Environment
Reference
De Vries, W., Kros, J., Reinds, G.J. and Butterbach-Bahl, K. 2011. Quantifying impacts of nitrogen use in European agriculture on global warming potential. Current Opinion in Environmental Sustainability 3: 291-302.

Background
In a themed issue of Current Opinion in Environmental Sustainability dealing with the role of nitrogen in climate change, the two editors of the issue (Kroeze and Bouwman, 2011) note that the natural nitrogen cycle has been accelerating rapidly due to intensified human activities since the beginning of the Industrial Revolution; and as a result, they say that "more reactive nitrogen (Nr) is emitted into the environment ... causing multiple environmental problems, including eutrophication, acidification, disturbance of tropospheric ozone chemistry and [last of all, most appropriately] global warming."

What was done
In one of the articles of the themed issue, de Vries et al. summarize current knowledge on the impacts of increases in nitrogen (Nr) use in agriculture - primarily due to "Nr inputs by fertilizer and manure and NH3 deposition and indirect impacts due to Nr leaching and NH3 deposition caused by agriculture on terrestrial, aquatic and marine ecosystems" - on "the global warming potential (GWP) by its impact on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) emissions from agricultural and terrestrial non-agricultural systems and from aquatic and marine ecosystems."

What was learned
In light of the information they gleaned from the pertinent scientific literature, the four scientists concluded that "direct and indirect N2O emissions induced by the use of Nr in agriculture are likely compensated by carbon sequestration," noting that "these results are in line with global estimates based on model results by Zaehle et al. (2010) and the meta data analysis of Liu and Greaver (2009), both indicating that N-driven CO2 uptake offsets the N stimulation of N2O emission and reduced CH4 uptake from ecosystems," adding that "due to the limitation of Nr in (semi-) natural ecosystems, increased N deposition usually increases net primary production and the fixation of CO2 by terrestrial systems (Townsend et al., 1996)," with the best example of this phenomenon being the stimulating effect of Nr deposition on the growth of forests, citing the work of Nadelhoffer et al. (1999), de Vries et al. (2006, 2008, 2009) and Quinn et al. (2010).

What it means
The chief result of de Vries et al.'s review of the scientific literature clearly demonstrates, as they describe it, that "the increase in global warming potential caused by elevated N2O emission due to Nr use in agriculture is completely counteracted by elevated carbon sequestration in non-agricultural systems."

References
de Vries, W., Reinds, G.J., Gundersen, P. and Sterba, H. 2006. The impact of nitrogen deposition on carbon sequestration in European forests and forest soils. Global Change Biology 12: 1151-1173.

de Vries, W., Solberg, S., Dobbertin, M., Sterba, H., Laubhann, D., Reinds, G.J., Nabuurs, G.J., Hundersen, P. and Sutton, M.A. 2008. Ecologically implausible carbon response? Nature 451: E1-E3.

de Vries, W., Solberg, S., Dobbertin, M., Sterba, H., Laubhann, D., van Oijen, M., Evans, C., Gundersen, P., Kros, J., Wamelink, G.W.W., Reinds, G.J. and Sutton, M.A. 2009. The impact of nitrogen deposition on carbon sequestration by European forests and heathlands. Forest Ecology and Management 258: 1814-1823.

Kroeze, C. and Bouwman, L. 2011. The role of nitrogen in climate change. Current Opinion in Environmental Sustainability 3: 279-280.

Liu, L. and Greaver, T.L. 2009. A review of nitrogen enrichment effects on three biogenic GHGs: the CO2 sink may be largely offset by stimulated N2O and CH4 emission. Ecology Letters 12: 1103-1117.

Nadelhoffer, K.J., Emmett, B.A., Gundersen, P., Kjonaas, O.J., Koopmans, C.J., Schleppi, P., Tietema, A. and Wright, R.F. 1999. Nitrogen deposition makes a minor contribution to carbon sequestration in temperate forests. Nature 398: 145-148.

Quinn, T.R., Canham, C.D., Weathers, K.C. and Goodale, C.L. 2010. Increased tree carbon storage in response to nitrogen deposition in the US. Nature Geoscience 3: 13-17.

Townsend, A.R., Braswell, B.H., Holland, E.A. and Penner, J.E. 1996. Spatial and temporal patterns in terrestrial carbon storage due to deposition of fossil fuel nitrogen. Ecological Applications 6: 806-814.

Zaehle, S., Friend, A.D., Dentener, F., Friedlingstein, P., Peylin, P. and Schulz, M. 2010. Carbon and nitrogen cycle dynamics in the O-CN land surface model: 2. Role of the nitrogen cycle in the historical terrestrial carbon balance. Global Biogeochemical Cycles 24: 10.1029/2009GB003522.

Reviewed 29 February 2012