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

^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

View larger version (31K): [in a new window]   Fig. 1. Map of the study site.

View larger version (41K): [in a new window]   Fig. 2. Water table contours (meters above sea level) for Waste Application Field (WAF) 1 with horizontal gradient vectors at two different dates to show seasonal consistency. Black symbols indicate location of well nests and dashed line represents the stream. The contour interval is 0.5 m. The length of vectors represents size of the hydraulic gradient. Transect 1, ; Transect 2, •; Transect 3, .

View larger version (37K): [in a new window]   Fig. 3. Water table contours (meters above sea level) for Waste Application Field (WAF) 2 with horizontal gradient vectors at two different dates to show seasonal consistency. Black symbols indicate location of well nests and dashed line represents the stream. The contour interval is 0.2 m. The length of vectors represents size of the hydraulic gradient. Transect 1, ; Transect 2, •; Transect 3, .

View larger version (29K): [in a new window]   Fig. 4. Chloride concentrations in ground water from shallow and deep wells averaged over the 36-mo sampling period.

View larger version (31K): [in a new window]   Fig. 5. Nitrate N and Cl concentrations and [Cl] to [nitrate N] ratios in shallow ground water moving from waste application fields (WAFs) to stream. Values are means for all samples taken from the shallow wells at each nest over a 36-mo period.

View larger version (14K): [in a new window]   Fig. 6. Dissolved organic carbon (DOC) concentrations in shallow ground water moving from waste application fields (WAFs) to the stream. Values are means for all samples taken from the shallow wells of each nest over a 36-mo period.

View larger version (25K): [in a new window]   Fig. 7. 15N natural abundance ratios for nitrate N in shallow ground water moving from waste application fields (WAFs) to the stream. The horizontal dashed lines represent the upper end of the range of 15N natural abundance ratios reported for fertilizer N sources.

View larger version (23K): [in a new window]   Fig. 8. Relationships between 18O of nitrate and 15N of nitrate in shallow ground water moving from waste application fields (WAFs) to the stream. Solid line represents the predicted 18O-nitrate vs. 15N-nitrate relationship when nitrate N is denitrified in the system. Dashed lines represent predicted 18O-nitrate vs. 15N-nitrate relationships when fertilizer N and animal waste N are nitrified.

View larger version (14K): [in a new window]   Fig. 9. Comparison 15N natural abundance ratios for nitrate N in water from the stream and from wells in the waste application fields (WAFs) over a 24-mo period.