Anne B. Hoos and Gerard McMahon have authored this work as part of their official duties as employees of the US Government.
Spatial analysis of instream nitrogen loads and factors controlling nitrogen delivery to streams in the southeastern United States using spatially referenced regression on watershed attributes (SPARROW) and regional classification frameworks†
Article first published online: 18 JUN 2009
This article is a US Government work and is in the public domain in the USA. Published in 2009 by John Wiley & Sons, Ltd.
Volume 23, Issue 16, pages 2275–2294, 30 July 2009
How to Cite
Hoos, A. B. and McMahon, G. (2009), Spatial analysis of instream nitrogen loads and factors controlling nitrogen delivery to streams in the southeastern United States using spatially referenced regression on watershed attributes (SPARROW) and regional classification frameworks. Hydrol. Process., 23: 2275–2294. doi: 10.1002/hyp.7323
This article is a US Government work and is in the public domain in the USA.
- Issue published online: 17 JUL 2009
- Article first published online: 18 JUN 2009
- Manuscript Accepted: 10 MAR 2009
- Manuscript Received: 24 NOV 2008
- National Water-Quality Assessment (NAWQA)
- total nitrogen;
- spatially referenced regression;
- watershed models;
- landscape attenuation
Understanding how nitrogen transport across the landscape varies with landscape characteristics is important for developing sound nitrogen management policies. We used a spatially referenced regression analysis (SPARROW) to examine landscape characteristics influencing delivery of nitrogen from sources in a watershed to stream channels. Modelled landscape delivery ratio varies widely (by a factor of 4) among watersheds in the southeastern United States—higher in the western part (Tennessee, Alabama, and Mississippi) than in the eastern part, and the average value for the region is lower compared to other parts of the nation. When we model landscape delivery ratio as a continuous function of local-scale landscape characteristics, we estimate a spatial pattern that varies as a function of soil and climate characteristics but exhibits spatial structure in residuals (observed load minus predicted load). The spatial pattern of modelled landscape delivery ratio and the spatial pattern of residuals coincide spatially with Level III ecoregions and also with hydrologic landscape regions. Subsequent incorporation into the model of these frameworks as regional scale variables improves estimation of landscape delivery ratio, evidenced by reduced spatial bias in residuals, and suggests that cross-scale processes affect nitrogen attenuation on the landscape. The model-fitted coefficient values are logically consistent with the hypothesis that broad-scale classifications of hydrologic response help to explain differential rates of nitrogen attenuation, controlling for local-scale landscape characteristics. Negative model coefficients for hydrologic landscape regions where the primary flow path is shallow ground water suggest that a lower fraction of nitrogen mass will be delivered to streams; this relation is reversed for regions where the primary flow path is overland flow. Published in 2009 by John Wiley & Sons, Ltd.