English: Map of alkalinity in surface waters in the U.S.

This map was made by the EPA and shows alkalinity values for surface waters the Untied States. According to the EPA, this map provides a general 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.