Spatial Patterns in Amount and Form of River Nitrogen Export

Spatial Patterns in Amount and Form OF River Nitrogen Export 

During the last several decades there have been many studies quantifying and characterizing N export by individual rivers to the coastal zone through direct measurements of N concentrations and water discharge (e.g. Boynton et al., 1995  

Eyre and Pont, 2003 Jordan et ai, 2003 Nixon et al., 1995 Wollast, 1983 Table Al). In addition, a number of relatively complex, deterministic models of river nitrogen flux have been developed and applied to individual rivers (e.g., GWLF, Haith and Shoemaker, 1987 Lee et al., 1999 HSPF, BickneU et al., 1997 Fdoso et al., 2004 SWAT, Srinivasan et al., 1993). Several of these, as well as other models, have been described recently in Alexander et al. (2002). 

Relatively few large rivers account for a large proportion of the N exported to coastal zones globaUy for ah N forms, based on NEWS model predictions. For example, the 25 rivers with the greatest water discharge globaUy ( 0.5% of the rivers with a watershed 2500 km ) account for approximately half of the exported DIN and DON, and about a quarter of the exported PN, globaUy (Table 9.1). Some of 

If we distinguish N export by form, at the global scale, DIN and PN export are approximately equal in magnitude ( 25 Tg yr and 30 Tg yr respectively), with 

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