Dominance of organic nitrogen from headwater streams to large rivers across the conterminous United States
Article first published online: 18 JAN 2007
Copyright 2007 by the American Geophysical Union.
Global Biogeochemical Cycles
Volume 21, Issue 1, March 2007
How to Cite
2007), Dominance of organic nitrogen from headwater streams to large rivers across the conterminous United States, Global Biogeochem. Cycles, 21, GB1003, doi:10.1029/2006GB002730., , , and (
- Issue published online: 18 JAN 2007
- Article first published online: 18 JAN 2007
- Manuscript Accepted: 25 SEP 2006
- Manuscript Revised: 18 SEP 2006
- Manuscript Received: 27 MAR 2006
 The frequency and magnitude of hypoxic areas in coastal waterbodies are increasing across the globe, partially in response to the increase in nitrogen delivery from the landscape (Diaz, 2001; Rabalais et al., 2002). Although studies of annual total nitrogen and nitrate yields have greatly improved understanding of the contaminant sources that contribute to riverine nitrogen loads (Alexander et al., 2000; Caraco and Cole, 1999), the emphasis of these studies on annual timescales and selected nitrogen forms is not sufficient to understand the factors that control the cycling, transport, and fate of reactive nitrogen. Here we use data from 850 river stations to calculate long-term mean-annual and interannual loads of organic, ammonia, and nitrate-nitrite nitrogen suitable for spatial analysis. We find that organic nitrogen is the dominant nitrogen pool within rivers across most of the United States and is significant even in basins with high anthropogenic sources of nitrogen. Downstream organic nitrogen patterns illustrate that organic nitrogen is an abundant fraction of the nitrogen loads in all regions. Although the longitudinal patterns are not consistent across regions, these patterns are suggestive of cycling between ON and NO3− on seasonal timescales influenced by land use, stream morphology, and riparian connectivity with active floodplains. Future regional studies need to incorporate multinitrogen species at intraannual timescales, as well as stream characteristics beyond channel depth, to elucidate the roles of nitrogen sources and in-stream transformations on the fate and reactivity of riverine nitrogen transported to coastal seas.