From Missing Source to Missing Sink: Long-Term Changes in the Nitrogen Budget of a Northern Hardwood Forest

TitleFrom Missing Source to Missing Sink: Long-Term Changes in the Nitrogen Budget of a Northern Hardwood Forest
Publication TypeJournal Article
Year of Publication2013
AuthorsYanai, RD, Vadeboncoeur, MA, Hamburg, SP, Arthur, MA, Fuss, CB, Groffman, PM, Siccama, TG, Driscoll, CT
JournalEnvironmental Science & Technology
Volume47
Issue20
Pagination11440 - 11448
Date Published2013/10/15/
ISBN Number0013-936X
Abstract

Biogeochemical monitoring for 45 years at the Hubbard Brook Experimental Forest in New Hampshire has revealed multiple surprises, seeming contradictions, and unresolved questions in the long-term record of ecosystem nitrogen dynamics. From 1965 to 1977, more N was accumulating in living biomass than was deposited from the atmosphere; the ?missing? N source was attributed to biological fixation. Since 1992, biomass accumulation has been negligible or even negative, and streamwater export of dissolved inorganic N has decreased from ?4 to ?1 kg of N ha?1 year?1, despite chronically elevated atmospheric N deposition (?7 kg of N ha?1 year?1) and predictions of N saturation. Here we show that the ecosystem has shifted to a net N sink, either storing or denitrifying ?8 kg of N ha?1 year?1. Repeated sampling over 25 years shows that the forest floor is not detectably accumulating N, but the C:N ratio is increasing. Mineral soil N has decreased nonsignificantly in recent decades, but the variability of these measurements prevents detection of a change of

URLhttp://dx.doi.org/10.1021/es4025723
Short TitleEnviron. Sci. Technol.