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USGS Circular 1350: Nutrients in the Nation's Streams and Groundwater

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Chapter 3: NAWQA’s Approach to Nutrient Assessment

Table 3-1. Each stream sampled by NAWQA was classified according to the dominant land uses in its watershed.
[Modified from Gilliom and others (2006). The land-use data set used for these classifications was an enhanced version of the USGS 1992 National Land Cover Data (NLCD) (Nakagaki and others, 2007)]


Watershed land-use criteria


> 50 percent agricultural land and
  < 5 percent urban land


> 25 percent urban land and
< 25 percent agricultural land


  < 5 percent urban land and
< 25 percent agricultural land


All other combinations of urban, agricultural, and undeveloped land


How this table was made:

This table defines the national land-use classifications used to characterize stream sites sampled by NAWQA. The objective was to establish a consistent approach for national analysis. Briefly, the percentage of land area within each watershed, which was comprised of up to 25 different land-cover types was determined using national land-cover data. The total agricultural land, total urban land, and total undeveloped land were calculated (as a percentage of total watershed area) by summing the percentages of land cover classifications in each of these three categories. Each site then was assigned to one of 4 national land-use classes (agricultural, urban, undeveloped, and mixed land use), depending on the amount of agricultural, urban, and undeveloped land within the watershed, using the criteria listed in this table. Ultimately, a few sites had their classifications adjusted if one or more land uses makes a disproportionately large or small contribution (relative to its percentage of land use in the watershed) to streamflow at the site because of water management practices or natural variations in precipitation and runoff. For more information see Gilliom and others (2006).

Land cover was obtained from the Enhanced National Land Cover Data 1992 (NLCDe 92) described by Nakagaki and others (2007), which classifies land cover for each 30- by 30-meter area of land in the conterminous U.S. NLCDe 92 was based primarily on 1992 National Land Cover Data (NLCD 92), which was derived from satellite imagery (U.S. Geological Survey, 1999; Vogelmann and others, 2001). Nakagaki and others (2007) produced NLCDe 92 by reclassifying NLCD 92 using enhanced historical U.S. Geological Survey Land Use and Land Cover (LULC) from Price and others (2007). The LULC data set was derived from aerial photographs and better represents certain land categories that are not well-depicted by satellite imagery (“residential;” “orchards, groves, vineyards, nurseries, and ornamental horticultural areas;” and “tundra”).

The watersheds for the NAWQA water sampling sites are described in Nakagaki and Wolock (2005).

References Cited:

Gilliom, R.J.; Barbash, J.E.; Crawford, C.G.; Hamilton, P.A.; Martin, J.D.; Nakagaki, Naomi; Nowell, L.H.; Scott, J.C.; Stackelberg, P.E.; Thelin, G.P.; and Wolock, D.M.; 2006, Pesticides in the Nation's streams and ground water, 1992–2001—the quality of our Nation's waters: U.S. Geological Survey Circular 1291, 172 p. (Also available at

Nakagaki, N., Price, C.V., Falcone, J.A., Hitt, K.J., Ruddy, B.C., 2007, Enhanced national land cover data 1992 (NLCDe 92), digital data, accessed September 2005, at

Nakagaki, Naomi, and Wolock, D.M., 2005, Estimation of agricultural pesticide use in drainage basins using land cover maps and county pesticide data: U.S. Geological Survey Open-File Report 2005-1188. Available at

Price, C.V., Nakagaki, N., Hitt, K.J., Clawges, R.M., 2007, Enhanced historical land-use and land-cover data sets of the U.S. Geological Survey: U.S. Geological Survey Data Series 240, accessed August 2007, at

U.S. Geological Survey, 1999, National land cover data 1992 (NLCD 92), available at

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., Wylie, B.K., and Van Driel, N., 2001, Completion of the 1990’s National Land Cover Dataset for the conterminous United States from Landsat Thematic Mapper data and ancillary data sources: Photogrammetric Engineering and Remote Sensing, v. 67, p. 650-662.

For more information contact:

Jo Ann M. Gronberg, NAWQA Nutrient Synthesis
U.S. Geological Survey
345 Middlefield Road
Mail Stop 470
Menlo Park, California 94025
Voice: 650-329-4423
Fax: 650-329-4463


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