Toward the improvement of total nitrogen deposition budgets in the United States

Frameworks for limiting ecosystem exposure to excess nutrients and acidity require accurate and complete deposition budgets of reactive nitrogen (Nr). While much progress has been made in developing total Nr deposition budgets for the U.S., current budgets remain limited by key data and knowledge ga...

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Bibliographic Details
Published in:	The Science of the total environment Vol. 691; pp. 1328 - 1352
Main Authors:	Walker, J.T., Beachley, G., Amos, H.M., Baron, J.S., Bash, J., Baumgardner, R., Bell, M.D., Benedict, K.B., Chen, X., Clow, D.W., Cole, A., Coughlin, J.G., Cruz, K., Daly, R.W., Decina, S.M., Elliott, E.M., Fenn, M.E., Ganzeveld, L., Gebhart, K., Isil, S.S., Kerschner, B.M., Larson, R.S., Lavery, T., Lear, G.G., Macy, T., Mast, M.A., Mishoe, K., Morris, K.H., Padgett, P.E., Pouyat, R.V., Puchalski, M., Pye, H.O.T., Rea, A.W., Rhodes, M.F., Rogers, C.M., Saylor, R., Scheffe, R., Schichtel, B.A., Schwede, D.B., Sexstone, G.A., Sive, B.C., Sosa Echeverría, R., Templer, P.H., Thompson, T., Tong, D., Wetherbee, G.A., Whitlow, T.H., Wu, Z., Yu, Z., Zhang, L.
Format:	Journal Article
Language:	English
Published:	Netherlands Elsevier B.V 15-11-2019
Subjects:	Ammonia Dry deposition Organic nitrogen Oxidized nitrogen Reactive nitrogen Wet deposition Ammonia Organic nitrogen Wet deposition Dry deposition Reactive nitrogen Oxidized nitrogen
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Summary:	Frameworks for limiting ecosystem exposure to excess nutrients and acidity require accurate and complete deposition budgets of reactive nitrogen (Nr). While much progress has been made in developing total Nr deposition budgets for the U.S., current budgets remain limited by key data and knowledge gaps. Analysis of National Atmospheric Deposition Program Total Deposition (NADP/TDep) data illustrates several aspects of current Nr deposition that motivate additional research. Averaged across the continental U.S., dry deposition contributes slightly more (55%) to total deposition than wet deposition and is the dominant process (>90%) over broad areas of the Southwest and other arid regions of the West. Lack of dry deposition measurements imposes a reliance on models, resulting in a much higher degree of uncertainty relative to wet deposition which is routinely measured. As nitrogen oxide (NOx) emissions continue to decline, reduced forms of inorganic nitrogen (NHx = NH3 + NH4+) now contribute >50% of total Nr deposition over large areas of the U.S. Expanded monitoring and additional process-level research are needed to better understand NHx deposition, its contribution to total Nr deposition budgets, and the processes by which reduced N deposits to ecosystems. Urban and suburban areas are hotspots where routine monitoring of oxidized and reduced Nr deposition is needed. Finally, deposition budgets have incomplete information about the speciation of atmospheric nitrogen; monitoring networks do not capture important forms of Nr such as organic nitrogen. Building on these themes, we detail the state of the science of Nr deposition budgets in the U.S. and highlight research priorities to improve deposition budgets in terms of monitoring and flux measurements, leaf- to regional-scale modeling, source apportionment, and characterization of deposition trends and patterns. [Display omitted] •Deposition budgets for inorganic nitrogen have improved over the last decade in the U.S.•Important data and knowledge gaps in monitoring and modeling of total nitrogen deposition remain.•Expanded monitoring of deposition in agricultural and urban areas is needed.•Monitoring of organic N deposition and improvement of organic N in atmospheric models is needed.•Land use specific modeled deposition estimates are needed for critical load assessments.
Bibliography:	Recently retired
ISSN:	0048-9697 1879-1026
DOI:	10.1016/j.scitotenv.2019.07.058