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Nitrate Movement in Shallow Ground Water from Swine‐Lagoon‐Effluent Spray Fields Managed under Current Application Regulations
Author(s) -
Israel Daniel W.,
Showers William J.,
Fountain Matthew,
Fountain John
Publication year - 2005
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2004.0338
Subject(s) - nitrate , denitrification , environmental science , effluent , groundwater , hydrology (agriculture) , riparian zone , surface water , water quality , water table , nitrogen , environmental chemistry , environmental engineering , chemistry , ecology , geology , geotechnical engineering , organic chemistry , habitat , biology
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 δ 15 N 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 δ 18 O and δ 15 N enrichment of nitrate in ground water throughout the WAF–riparian system indicated that denitrification has not caused significant 15 N enrichment of nitrate. Over a 24‐mo period, δ 15 N ratios for nitrate N in the stream approached δ 15 N 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.