This map provides a synoptic illustration of the national patterns of surface water alkalinity in the conterminous United States. Alkalinity is the most readily available measure of the acid-neutralizing capacity of surface waters and provides a reasonable estimate of the relative potential sensitivity of lakes and streams to acidic deposition. Although the actual sensitivity of a water body depends on many watershed characteristics and processes, the low-alkalinity areas on the map indicate where sensitive surface waters are most likely to be found. 

The map is based on alkalinity data from approximately 39,000 lake and stream sites and the associations of the data values with factors such as land use, physiography, geology, and soils. Data were acquired from a variety of sources including federal and state agencies, university researchers, and private corporations. In many of the areas represented by a specific alkalinity range, an even greater range was observed in the water quality data. The shading on the map indicates the range of alkalinity within which the mean annual values of most of the surface waters of the area fall.

The mapping of surface water alkalinity began in 1981 at the U.S. EPA's Environmental Research Laboratory in Corvallis, Oregon, as a first step in a comprehensive project to identify lakes and streams potentially sensitive to acidification. A "first cut" national map, based on data from approximately 2500 lakes and streams, was published in 1982. More detailed regional alkalinity maps were developed soon after. These regional maps provided better illustrations of the patterns in low alkalinity areas and provided rationale for selecting geographic areas for more detailed studies. The sampling design of the EPA's National Surface Water Survey (NSWS) in the mid 1980’s was based heavily on these regional maps. In 1988, revision of the alkalinity maps based on EPA's NSWS data, other surface water alkalinity data, and larger-scale compilation techniques was completed, resulting in this national map. 

	Literature cited:

	Omernik, J.M., and C.F. Powers. 1982. Total alkalinity of surface waters -- a national map. EPA-600/D-82-333. Corvallis Environmental Research Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon. 7p.

	Omernik, J.M., and C.F. Powers. 1983. Total alkalinity of surface waters -- a national map. Annals of the Association of American Geographers 73(1):133-136.

	Omernik, J.M., and A.J. Kinney. 1985. Total alkalinity of surface waters: a map of the New England and New York region. EPA-600/D-84-216. Corvallis Environmental Research Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon. 11p.

	Omernik, J.M., and G.E. Griffith. 1985. Total alkalinity of surface waters: a map of the Upper Midwest region. EPA-600/D-85-043. Corvallis Environmental Research Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon. 19p. 

	Omernik, J.M., and G.E. Griffith. 1986. Total alkalinity of surface waters: a map of the Upper Midwest region of the United States. Environmental Management 10(6):829-839.

	Omernik, J.M., and G.E. Griffith. 1986. Total alkalinity of surface waters: a map of the western region. EPA-600/D-85-219. Corvallis Environmental Research Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon. 28p.

For information on the compilation and availability of the alkalinity maps, contact:  Glenn Griffith, USGS, c/o U.S. EPA, 200 S.W. 35th St., Corvallis, Oregon 97333, (541) 754-4465, griffith.glenn@epa.gov. Alternate: James M. Omernik, USGS, c/o U.S. EPA, 200 S.W. 35th St. Corvallis, Oregon 97333, (541) 754-4458, omernik.james@epa.gov.

Alkalinity maps identify areas where lakes and streams may be sensitive to acidification.

Electronic versions of maps and posters as well as other resources are available at:  http://www.epa.gov/wed/pages/ecoregions.htm.  Alkalinity maps were digitized at 1:250,000 or smaller scales 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.

http://www.epa.gov/nheerl/

Publication date

None

None. Please check sources, scale, accuracy, currentness and other available information. Please confirm that you are using the most recent copy of both data and metadata.  Acknowledgement of the EPA would be appreciated.

The AKCODE classes and microeqv_l values denote the capacity of lakes and streams to neutralize acidity.  Lower values denote greater sensitivity to acid precipitation.

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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