Variability of Anaerobic Animal Waste Lagoon delta¹⁵N Source Signatures

Abstract

High ammonium-N concentrations derived from animal wastes stored and partially treated in earthen anaerobic lagoons at confined feeding facilities can seep to groundwater. δ¹⁵N-NH₄ ⁺ values from +2.0 to +59.1‰ in 13 lagoons complicate identification of lagoon seepage as well as land-applied lagoon effluent in ground and surface waters. The spectrum of δ¹⁵N values requires site-specific isotope characterization of the potential source. Feed and fresh manure and urine δ¹⁵N values indicate that most N isotopic fractionation occurs after excretion. Lagoon management clearly affects enrichment. δ¹⁵N-total Kjeldahl N (TKN) and δ¹⁵N-NH₄ ⁺ within each lagoon were not statistically different. δ¹⁵N-NH₄ ⁺ within the top 1.5 m of the lagoons was spatially uniform (CV [coefficient of variation] < 5%).

Keywords:

• δ¹⁵N
• stable N isotopes
• N contamination
• animal waste lagoon
• source characterization

Acknowledgement

This research was supported by the Nebraska Department of Environmental Quality. This manuscript has been assigned Journal Series no. 15235, Agricultural Research Division, University of Nebraska. The authors thank B. Genna and T. McDade of the North Carolina State University Stable Isotope Laboratory for their review comments.

Notes

∗Data from Gormly and Spalding, 1974.