Abstract
Most nitrogen (N) assimilation in lake and marine ecosystems is often subsequently released via autochthonous dissolved organic nitrogen (DON) production, but autochthonous DON production has yet to be quantified in flowing waters. We measured in‐stream DON production following 24 h 15N‐nitrate () tracer additions in 36 headwater streams, a subset of sites from the second Lotic Intersite Nitrogen eXperiment. Streams were located in five North American ecoregions and drained basins dominated by native vegetation, agriculture, or urban land use. Using a two‐compartment model, we could quantify DON production in 15 streams as a function of DO15N derived from 15N 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 uptake when we used N biomass estimates based on N assimilated over 1 d (measured directly from the 15N additions). Median DON production was 17% of total uptake when we used N assimilated over 42 d (extrapolated from previous 15N tracer studies). Variation in DON production was positively correlated with ecosystem respiration, indicating that stream heterotrophy may influence DON production. In‐stream DON production was similar in magnitude to stream denitrification and nitrification, indicating that the production of autochthonous DON can represent a substantial transformation of stream N. Our results confirm that headwater streams can quickly convert inorganic N into organic forms, although the ultimate fate of DON remains unclear.
Highlights
Most nitrogen (N) assimilation in lake and marine ecosystems is often subsequently released via autochthonous dissolved organic nitrogen (DON) production, but autochthonous DON production has yet to be quantified in flowing waters
Other factors were variable (Table 1); mean stream temperature varied from 9.9uC to 25.3uC, NHz 4 concentrations varied from 1 to 2204 mg N L21, and ambient soluble reactive phosphorus (SRP) concentrations varied from, 1 to 311 mg P L21
DON production was statistically significant in 15 streams, where DO15N flux increased with distance downstream
Summary
Most nitrogen (N) assimilation in lake and marine ecosystems is often subsequently released via autochthonous dissolved organic nitrogen (DON) production, but autochthonous DON production has yet to be quantified in flowing waters. Production of autochthonous dissolved organic matter (DOM, a portion of which is DON) by aquatic biota can occur through several mechanisms, including the release of cell constituents via death, senescence, viral lysis, or herbivory (Baines and Pace 1991; Bertilsson and Jones 2003), and these processes occur in both autotrophs (e.g., algae, macrophytes) and heterotrophs (i.e., bacteria, fungi). Aquatic DON production is usually attributed to extracellular release via autotrophs in both marine and lake ecosystems, and we predict that this mechanism will apply in streams as well
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
