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. 15N-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 15N values requires site-specific isotope characterization of the potential source. Feed and fresh manure and urine 15N values indicate that most N isotopic fractionation occurs after excretion. Lagoon management clearly affects enrichment. 15N-total Kjeldahl N (TKN) and 15N-NH4+ within each lagoon were not statistically different. 15N-NH4+ within the top 1.5 m of the lagoons was spatially uniform (CV [coefficient of variation] 5%).