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

Abstract

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.

Nitrate fate and transport through current and former depressional wetlands in an agricultural landscape, Choptank Watershed, Maryland, United States

“…Oxic groundwater was common beneath upland fields surrounding the depressions (figures 8c and 10; table 1). Water chemistry reflected agricultural influences similar to those observed elsewhere on the Delmarva Peninsula (Denver 1989;Debrewer et al 2008) and the wider Coastal Plain (Ator 2008), including elevated concentrations of Ca, Mg, NO 3 , and Cl, presumably from agricultural applications of lime, fertilizer, manure, and potash (figure 9b). Nitrate concentrations generally exceeded 10 mg NO 3 -N L -1 (10 ppm NO 3 -N) beneath agricultural uplands, and the addition of ions from agricultural sources resulted in the specific conductance of groundwater being elevated relative to the dilute baseline conditions seen in upland forested areas (figures 8b and 9; table 1).…”

Suburban Groundwater Quality as Influenced by Turfgrass and Septic Sources, Delmarva Peninsula, USA

“…Use of nitrate concentration alone to determine sources can be appropriate when groundwater is monitored for nitrate immediately below the water table or in areas where only one land use has dominated the landscape for many decades. However, nitrate concentrations alone are often not sufficient for understanding the source of N because of the slow movement of groundwater, potential for redox changes over time in aquifers, and transport of ions from upgradient land uses to deeper depths in down-gradient parts of the groundwater system (Böhlke and Denver, 1995;Debrewer et al, 2008).…”

Response of barley to root colonization byPseudomonassp. DSMZ 13134 under laboratory, greenhouse, and field conditions

“…However, the negative side-effects of agrochemicals (for example, contamination of ground water, suppression of beneficial insect populations, selection of resistant strains, and health hazards for humans) have driven farmers to seek alternative means of pest control (Debrewer et al 2008;Costello et al 2009;Landgren et al 2009). The use of rhizosphere bacteria [plant growth-promoting bacteria, PGPB (Bashan and Holguin 1998)] organically improves crop yield and plant health.…”