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This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Debrewer, L. M. Articles by Denver, J. M. PubMed PubMed Citation Articles by Debrewer, L. M. Articles by Denver, J. M. Agricola Articles by Debrewer, L. M. Articles by Denver, J. M. Related Collections Agricultural Pesticides Nitrogen Water Pollution Ground Water Quality

Temporal Trends in Nitrate and Selected Pesticides in Mid-Atlantic Ground Water

U.S. Geological Survey, Maryland-Delaware-D.C. Water Science Center, 5522 Research Park Drive, Baltimore, MD 21228

^* Corresponding author (lmdebrew{at}usgs.gov).

Received for publication December 26, 2007. Evaluating long-term temporal trends in regional ground-water quality is complicated by variable hydrogeologic conditions and typically slow flow, and such trends have rarely been directly measured. Ground-water samples were collected over near-decadal and annual intervals from unconfined aquifers in agricultural areas of the Mid-Atlantic region, including fractured carbonate rocks in the Great Valley, Potomac River Basin, and unconsolidated sediments on the Delmarva Peninsula. Concentrations of nitrate and selected pesticides and degradates were compared among sampling events and to apparent recharge dates. Observed temporal trends are related to changes in land use and chemical applications, and to hydrogeology and climate. Insignificant differences in nitrate concentrations in the Great Valley between 1993 and 2002 are consistent with relatively steady fertilizer application during respective recharge periods and are likely related to drought conditions in the later sampling period. Detecting trends in Great Valley ground water is complicated by long open boreholes characteristic of wells sampled in this setting which facilitate significant ground-water mixing. Decreasing atrazine and prometon concentrations, however, reflect reported changes in usage. On the Delmarva Peninsula between 1988 and 2001, median nitrate concentrations increased 2 mg per liter in aerobic ground water, reflecting increasing fertilizer applications. Correlations between selected pesticide compounds and apparent recharge date are similarly related to changing land use and chemical application. Observed trends in the two settings demonstrate the importance of considering hydrogeology and recharge date along with changing land and chemical uses when interpreting trends in regional ground-water quality.

Abbreviations: ESA, ethanesulfonic acid • OA, oxanilic acid • tau, Kendall's tau-b correlation coefficient • SF₆, sulfur hexafluoride • USEPA, United States Environmental Protection Agency