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United States Department of Agriculture

Agricultural Research Service

Title: Nitrate-Nitrogen, Landuse/Landcover, and Soil Drainage Associations at Multiple Spatial Scales

Authors
item Floyd, William - OREGON STATE UNIVERSITY
item Schoenholtz, Stephen - VIRGINIA TECH
item Griffith, Stephen
item Wigington, Parker - US EPA
item Steiner, Jeffrey

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 9, 2009
Publication Date: May 20, 2009
Citation: Floyd, W.C., Schoenholtz, S.H., Griffith, S.M., Wigington, P.J., Steiner, J.J. 2009. Nitrate-Nitrogen, Landuse/Landcover, and Soil Drainage Associations at Multiple Spatial Scales. Journal of Environmental Quality. 38:1473-1482.

Interpretive Summary: Control of non-point-source water pollution by nitrate requires knowledge of landuse and landcover influences in the landscape. Within the Calapooia Watershed of Western Oregon, we sampled water across the landscape with different kinds of landuse/landcover to gain a better understanding of relationships among landuse/lancover area of influence (scales), soil drainage, and dissolved nitrate-N dynamics with nitrate-N. We observed strong negative correlations between nitrate-N and proportion of woody vegetation during winter and spring. Poorly drained soils had moderate- to strong positive correlations with nitrate-N. Altering scale of analysis significantly changed correlations between nitrate-N and woody vegetation. We found that a greater than 150 m influence zone (IZs) generally being stronger than the watershed level during the winter. In contrast, nitrate-N correlations with poorly drained soil were generally stronger at the watershed scale than the 10- through 90-m IZs during winter and spring. These results indicate that scale of analysis is an important factor when determining associations between nitrate-N and proportion woody vegetation or poorly drained soils.

Technical Abstract: Control of non-point-source pollution of water to meet beneficial uses requires knowledge of landuse/landcover (LULC) influences at watershed scales. To gain a better understanding of relationships among LULC, soil drainage, and dissolved nitrate-N dynamics within the Calapooia Basin in Western Oregon, we selected 44 watersheds ranging in size between 3 and 33 km2 for monthly synoptic sampling of surface water quality between October 2003 and September 2004. Seasonal associations were examined between dissolved nitrate-N and proportion of woody vegetation or poorly drained soils at differing scales (10, 20, 30, 60, 90, 150, 300 m, and entire watershed), which we defined as Influence Zones (IZs), surrounding the stream network. Correlations between nitrate-N and proportion woody vegetation or poorly drained soil at each IZ were analyzed for significant differences using the Hotelling-Williams test. We observed strong negative correlations (r = -0.81 to -0.94) between nitrate-N and proportion of woody vegetation during winter and spring. Poorly drained soils had moderate- to strong positive correlations (r = 0.63 to 0.87) with nitrate-N. Altering scale of analysis significantly changed correlations between nitrate-N and woody vegetation, with IZs < 150-m generally being stronger than the watershed level during the winter. In contrast, nitrate-N correlations with poorly drained soil were generally stronger at the watershed scale than the 10- through 90-m IZs during winter and spring. These results indicate that scale of analysis is an important factor when determining associations between dissolved nitrate-N and proportion woody vegetation or poorly drained soils.

Last Modified: 10/1/2014
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