National Water-Quality Assessment--Potomac River Basin: Occurrence of Pesticides in Nested Watersheds in Virginia and West Virginia
By Joel D. Blomquist
Abstract
Pesticide monitoring in nested agricultural watersheds indicates that the occurrence of pesticides is scale dependent in the Shenandoah River Valley. The Muddy Creek site (14.2 square miles) contributes to the much larger watershed of the Shenandoah River site (3,040 square miles). Atrazine, deethylatrazine, simazine, and metolachlor were detected throughout the sampling period (March 1993 - April 1994) at both sites, with highest concentrations in runoff from spring storms. Alachlor and cyanazine were detected at both sites, but only during spring application. Prometone, an herbicide with widespread nonagricultural use, was detected in less than half of the samples from the Muddy Creek site, but in higher concentrations and in all samples from the Shenandoah River site. Eleven additional pesticides were detected at concentrations near or below the analytical reporting level at the Muddy Creek site, whereas only two additional pesticides were detected at the Shenandoah River site. Many pesticides are used in the Shenandoah River Valley but only those pesticides with extensive use are frequently detected in the Shenandoah River. Many additional pesticides, however, might be detectable only in small watersheds such as Muddy Creek because of less extensive use and lower application rates.
Citation
Blomquist, J. D., 1994, Occurrence of pesticides in nested watersheds in Virginia and West Virginia [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. 10.
