Quantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions

TitleQuantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions
Publication TypeJournal Article
Year of Publication2013
AuthorsJohnson, L, Tank, T, Hall, JL, Jr., RO, Mulholland, PJ, Hamilton, SK, H. Valett, M, Webster, JR, Bernot, MJ, William H. McDowell, Peterson, BJ, Thomas, SM
JournalLimnology and Oceanography
Volume58
Issue4
Pagination1271-1285
Accession NumberLUQ.1230
Abstract

Most nitrogen (N) assimilation in lake and marine ecosystems is often subsequently released via autochthonousdissolved organic nitrogen (DON) production, but autochthonous DON production has yet to be quantified inflowing waters. We measured in-stream DON production following 24 h15N-nitrate (NO{3) tracer additions in 36headwater streams, a subset of sites from the second Lotic Intersite Nitrogen eXperiment. Streams were located infive North American ecoregions and drained basins dominated by native vegetation, agriculture, or urban landuse. Using a two-compartment model, we could quantify DON production in 15 streams as a function of DO15Nderived from15N tracer in biomass compartments. The streams with detectable DON production had higher%modified land use (agriculture+urban) in their basins than did streams with undetectable DON production.Median DON production represented 8%of total NO{3uptake when we used N biomass estimates based on Nassimilated over 1 d (measured directly from the15N additions). Median DON production was 17%of total NO{3uptake when we used N assimilated over 42 d (extrapolated from previous15N tracer studies). Variation in DONproduction was positively correlated with ecosystem respiration, indicating that stream heterotrophy mayinfluence DON production. In-stream DON production was similar in magnitude to stream denitrification andnitrification, indicating that the production of autochthonous DON can represent a substantial transformation ofstream N. Our results confirm that headwater streams can quickly convert inorganic N into organic forms,although the ultimate fate of DON remains unclear.

URLhttp://www.treesearch.fs.fed.us/pubs/44613
Short TitleQuantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions