Human and non-human landscape characteristics relating to nutrient concentrations in streams vary regionally. Understanding the nature of these variations is necessary for the development of nutrient criteria in surface waters. In different parts of the country, geographic phenomena such as soils, vegetation, climate, and geology, cause nutrient concentrations to be different. Patterns in past and existing land use are also commonly related to these regional differences. 
Fourteen regions have been delineated in which there are broad scale similarities in ecosystems as well as in human and non-human related factors associated with nutrient concentrations in streams (U.S. EPA, 1998a). These 14 regions comprise aggregations of U.S. EPA Level III Ecoregions (Omernik, 1987; U.S. EPA, 1998b). Patterns in the spatial coincidence of characteristics including geology, soils, land use, geomorphology, and vegetation that are associated with geographic patterns in ecosystems, ecoregions, as well as these 14 aggregated ecoregions, are also spatially correlated with general patterns in nutrient concentrations in streams. It should be noted that while the Aggregated Level III Ecoregions are roughly the same level of detail as Level II Ecoregions, the Aggregated Level III Ecoregions are a new and different aggregation due to the narrower focus of the framework on landscape factors associated with nutrient concentrations in streams. Descriptions and further discussion of the regions can be found in Rohm et al., (2002).

	Rohm, C.M., J.M. Omernik, A.J. Woods, and J.L. Stoddard. 2002. Regional characteristics of nutrient concentrations in streams and their application to nutrient criteria development. Journal of the American Water Resources Association 38(1):1-27.

	U.S. EPA (U.S. Environmental Protection Agency), 1998a. National Strategy for the Development of Regional Nutrient Criteria. U.S. Environmental Protection Agency, Office of Water, Washington, D.C., EPA 822-R-98-002, 47 p.

	U.S. EPA (U.S. Environmental Protection Agency), 1998b. Level III Ecoregions of the Continental United States (revision of Omernik, 1987). U.S. Environmental Protection Agency, National Health and Environmental Effects Laboratory, Western Ecology Division, Corvallis, Oregon.

Comments and questions regarding the Level III and IV Ecoregions should be addressed to Glenn Griffith, USGS, c/o US EPA., 200 SW 35th Street, Corvallis, OR 97333, (541)-754-4465, email:griffith.glenn@epa.gov Alternate: James Omernik, USGS, c/o US EPA, 200 SW 35th Street, Corvallis, OR 97333, (541)-754-4458, email:omernik.james@epa.gov

 These aggregations of Level III Ecoregions help managers and researchers develop appropriate nutrient criteria and restoration methods.

Ecoregions were digitized at 1:250,000 scale and are intended for large geographic extents (i.e. states, multiple counties, or river basins). Use for smaller areas, such as individual counties or a 1:24,000 scale map boundary, is not recommended.

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Aggregated ecoregions for nutrient concentrations and criteria development are single purpose regions.  Although they are roughly at the same level of detail as Level II Ecoregions, they are a new and different aggregation due to the narrower focus of nutrient concentrations in streams.  The hierarchical levels of other ecoregion products is not preserved.

Shapefile name

USEPA

Tests for integrity have not been performed.

Features represented have not been tested for completeness

Data were collected using methods that have unknown accuracy (EPA National Geospatial Data Policy [NGDP] Accuracy Tier 10). For more information, please see EPA's NGDP at http://epa.gov/geospatial/policies.html)

Downloadable Data

Although these data have been processed successfully on a computer system at the Environmental Protection Agency, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data to evaluate data set limitations, restrictions or intended use. The U.S. Environmental Protection Agency shall not be held liable for improper or incorrect use of the data described and/or contained herein.

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