U.S. Environmental Protection Agency
EPA Science Advisory Board
Background Information

Document NameAtmospheric deposition of nitrogen in coastal waters: biogeochemical and ecological implications
Document AuthorPaerl, H. W.
Boynton, W.R.
Dennis, R.L.
Driscoll, C.T.
Greening, H.S.
Kremer, J.N.
Rabalais, N.N.
Seitzinger, S.P.
Short DescriptionPp 11-53 in R. A. Valigura, R. B. Alexander, M. S. Castro, T. P. Meyers, H. W. Paerl, P. E. Stacey and R.E. Turner (eds.), Nitrogen Loading in Coastal Water Bodies. An Atmospheric Perspective. Coastal and Estuarine Studies 57, American Geophysical Union, Washington, D.C.
CategorySubgroup 1: Characterization of the Cause(s) of Hypoxia
Publication Year2000

Abstract: Atmospheric deposition of nitrogen (AD-N, as wet deposition and dry deposition) is a significant and growing source of biologically available nitrogen (NOx, NH3/NH+4, and dissolved organic N (DON) entering nitrogen-limited estuarine and coastal waters (jointly termed coastal). AD-N ranges from 400 to > 1000 mg N m-2 yr-1, and represents from <10 to<40% of new N inputs in North American and European coastal waters downwind of emission sources. The relative contribution of AD-N to total external N loading depends on land use, watershed and airshed size, and hydrological and morphological characteristics (i.e., water retention time) of receiving waters. In heavily- impacted, N-sensitive waters, the ecological impacts of AD-N include accelerating primary production (eutrophication), which may yield a variety of negative impacts including increased algal bloom activity, toxicity, oxygen depletion (hypoxia) events, and food web alterations. Depending on their sources (i.e., agricultural, urban, industrial) certain forms of AD-N are increasing relative to others, leading to qualitative changes in deposition and biogeochemical response in receiving waters. Because phytoplankton and bacteria differentially utilize different forms of N, changes in the ratios of NH4+ to NOx and DON in AD-N may usher in community compositional changes. One example is the intensive animal operations in Western Europe and the U.S. Mid-Atlantic States, which are linked to regionally elevated NH4+ deposition rates. Experimental evidence indicates that increasing levels of AD-NH4+ enhance primary production, while favoring growth of specific phytoplankton functional groups. In addition, AD (as well as other sources of new N) enrichment alters the stoichiometric nutrient ratio (N:P:Si) which may impact phytoplankton community composition and growth potentials. Both quantitative and qualitative changes in AD-N inputs may be linked to eutrophication and algal bloom dynamics.