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This article in JEQ

  1. Vol. 34 No. 5, p. 1828-1842
     
    Received: Sept 1, 2004
    Published: Sept, 2005


    * Corresponding author(s): dan_israel@ncsu.edu
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doi:10.2134/jeq2004.0338

Nitrate Movement in Shallow Ground Water from Swine-Lagoon-Effluent Spray Fields Managed under Current Application Regulations

  1. Daniel W. Israel *a,
  2. William J. Showersb,
  3. Matthew Fountainb and
  4. John Fountainb
  1. a USDA-ARS and Department of Soil Science, North Carolina State University, Box 7619, Raleigh, NC 27695
    b J. Fountain, Department of Marine, Earth and Atmospheric Sciences, Box 8208, North Carolina State University, Raleigh, NC 27695

Abstract

Rapid increases in the swine (Sus scrofa domestica) population in the 1990s and associated potential for nitrate N pollution of surface waters led the state of North Carolina to adopt stringent waste management regulations in 1993. Our objectives were to characterize (i) nitrate N movement from waste application fields (WAFs) in shallow ground water, and (ii) soil, hydrologic, and biological factors influencing the amount of nitrate N in the adjacent stream. A ground water monitoring study was conducted for 36 mo on a swine farm managed under new regulations. Water table contours and lack of vertical gradients indicated horizontal flow over most of the site. Nitrate N concentrations in water from shallow wells in WAFs averaged 30 ± 19 mg L−1 and δ15N ratios for nitrate N were between +20 and +25 per mil. Nitrate N concentration decreased from field-edge to streamside wells by 22 to 99%. Measurement of δ18O and δ15N enrichment of nitrate in ground water throughout the WAF–riparian system indicated that denitrification has not caused significant 15N enrichment of nitrate. Over a 24-mo period, δ15N ratios for nitrate N in the stream approached δ15N ratios for nitrate N in ground water beneath WAFs indicating delivery of some waste-derived nitrate N to the stream in shallow ground water. Nitrate N concentrations in the stream were relatively low, averaging 1 mg L−1 Dilution of high nitrate N water in shallow horizontal flow paths with low nitrate N water from deeper horizontal flow paths at or near the stream, some denitrification as ground water discharges through the stream bottom, and some denitrification in riparian zone contributed to this low nitrate N concentration.

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