Variability of Anaerobic Animal Waste Lagoon delta¹⁵N Source Signatures

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%).