Estimating Contributions of Nitrate and Herbicides From Groundwater to Headwater Streams, Northern Atlantic Coastal Plain, United States¹

Abstract

Groundwater transport often complicates understanding of surface-water contamination. We estimated the regional flux of nitrate and selected herbicides from groundwater to nontidal headwater streams of the Atlantic Coastal Plain (New Jersey through North Carolina) based on late-winter or spring base-flow samples from 174 streams. Sampled streams were selected randomly, and flux estimates are based on resulting population estimates rather than on empirical models, which have been used previously for similar estimates. Base-flow flux in the estimated 8,834 headwater streams of the study area are an estimated 21,200 kg ⁄ day of nitrate (as N) and 5.83, 0.565, and 20.7 kg ⁄ day of alachlor, atrazine, and metolachlor (and selected degradates), respectively. Base-flow flux of alachlor and metolachlor is <3% of the total base-flow flux of those compounds plus degradates. Base-flow flux of nitrate and herbicides as a percentage of applications is typically highest in well-drained areas and lowest in areas with abundant poor drainage and anoxic conditions. In Coastal Plain watersheds of Albemarle and Pamlico Sounds, <2% of applied nitrogen reaches headwater streams as base flow. On the Delmarva Peninsula part of the Chesapeake Bay watershed, however, more than 10% of such applications are transported through groundwater to streams, and base-flow nitrate flux represents 70% of total nitrogen flux in headwater streams.(KEY TERMS: base-flow contaminant flux; surface water ⁄ groundwater interactions; nonpoint source pollution; nutrients; pesticides ⁄ herbicides; total maximum daily load (TMDL); groundwater discharge.) Ator, Scott W. and Judith M. Denver, 2012. Estimating Contributions of Nitrate and Herbicides from Groundwater to Headwater Streams, Northern Atlantic Coastal Plain, United States.

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

“…The USEPA's TMDLs require states and local governmental agencies to decrease or limit the total loads of contaminants to water bodies from both point and nonpoint sources to achieve water-quality standards (e.g., Delaware Department of Natural Resources and Environmental Control, 1998). Groundwater discharge is the primary source of N to streams on the Delmarva Peninsula, providing as much as 70% of the N flux, predominantly as nitrate (Ator and Denver, 2012;Domagalski et al, 2008).…”

Quantifying watershed‐scale groundwater loading and in‐stream fate of nitrate using high‐frequency water quality data

“…While field-based studies [Burns, 1998;Peterson et al, 2001;Duff et al, 2008;Mulholland et al, 2008Mulholland et al, , 2009Tank et al, 2008;Hall et al, 2009;Mulholland and Webster, 2010] and modeling approaches [Jaworski et al, 1992;Boynton et al, 1995;Alexander et al, 2000Alexander et al, , 2009Seitzinger et al, 2002;Boyer et al, 2006;Runkel, 2007;Ator and Denver, 2012] have provided much needed information on reach and watershed-scale nitrate dynamics, the limited spatial extent and/or low temporal resolution of discrete data collection continues to be a challenge for quantifying loads and interpreting drivers of change in watersheds. Recent studies have demonstrated that the collection and interpretation of high-frequency nitrate data collected using water quality sensors can be used to better quantify nitrate loads to sensitive stream and coastal environments [Ferrant et al, 2013;Bieroza et al, 2014;Pellerin et al, 2014], and provide insights into temporal nitrate dynamics that would otherwise be difficult to obtain using traditional field-based mass balance, solute injection, and/or isotopic tracer studies [Pellerin et al, 2009[Pellerin et al, , 2012Heffernan and Cohen, 2010;Sandford et al, 2013;Carey et al, 2014;Hensley et al, 2014Hensley et al, , 2015Outram et al, 2014;Crawford et al, 2015].…”

Assessing the Impacts of Future Climate Conditions on the Effectiveness of Winter Cover Crops in Reducing Nitrate Loads into the Chesapeake Bay Watersheds Using the SWAT Model

“…For example, winter cover crops (WCCs) are recommended as a costeffective agricultural BMP for reducing nitrate loads (McCarty et al, 2008;Ator and Denver, 2012). Due to the high efficiency of WCCs in reducing nitrate loads, both Federal and state governments provide cost-sharing programs to encourage local farmers to adopt WCCs (McCarty et al, 2008).…”