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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 21, GB1003, doi:10.1029/2006GB002730, 2007

Dominance of organic nitrogen from headwater streams to large rivers across the conterminous United States

Durelle Scott

U.S. Geological Survey, Reston, Virginia, USA


Judson Harvey

U.S. Geological Survey, Reston, Virginia, USA


Richard Alexander

U.S. Geological Survey, Reston, Virginia, USA


Gregory Schwarz

U.S. Geological Survey, Reston, Virginia, USA


Abstract

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.

Received 27 March 2006; accepted 25 September 2006; published 18 January 2007.

Keywords: biogeochemistry; nitrogen.

Index Terms: 0469 Biogeosciences: Nitrogen cycling; 0409 Biogeosciences: Bioavailability: chemical speciation and complexation; 0414 Biogeosciences: Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912); 0470 Biogeosciences: Nutrients and nutrient cycling (4845, 4850).

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Citation: Scott, D., J. Harvey, R. Alexander, and G. Schwarz (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.