National Water-Quality Assessment--Potomac River Basin: Benthic-Macroinvertebrate Communities and Water Quality in Agricultural and Urban Subbasins in the Great Valley Carbonate Subunit of the Potomac River Basin
By Humbert Zappia and S. K. Sorenson
Ecological surveys were conducted in the late summer of 1993 at 25 stream sites, as part of a synoptic sampling that related water quality to ecology and land use in the carbonate region of the Great Valley of the Potomac River Basin. The surveys included habitat assessments and benthic-macroinvertebrate sampling. Water samples were analyzed for physical properties, nutrients, major ions, and pesticides.
The Great Valley carbonate subunit encompasses about 2,500 square miles, or about 17 percent of the Potomac River basin. Drainage areas for the 25 sampling sites range from 3.6 to 20 square miles. Eighteen of the 25 drainage areas are dominated by agricultural land use, and the other 7 are strongly affected by local urban areas.
Sampling reaches at each site included two representatives of each geomorphic channel unit present in the stream segment--riffle, run, or pool. Composite benthic-macroinvertebrate samples were collected from the richest-targeted habitat, usually a riffle. Habitat assessment consisted of geomorphic characterizations of the channel, bank, and flood plain. Ecological conditions were described using community structure information, including taxa richness, diversity, functional feeding groups, and mode of existence.
Zappa, Humbert, and Sorenson, Stephen K., 1994, Benthic-macroinvertebrate communities and water quality in agricultural and urban subbasins in the Great Valley carbonate subunit of the Potomac River basin [abs.] : in Sorenson, Stephen K., ed., 1994, Proceedings Abstracts, American Water Resources Association's symposium on the National Water-Quality Assessment Program--November 7-9, 1994, Chicago, Illinois: U.S. Geological Survey Open-File Report 94-397, p. 18.