Impact of Lagoon Leakage at Confined Animal Feeding Operations in Nebraska on Shallow Ground Water Nitrate Concentrations and N-Isotope Variability

The two-year study of the environmental impact of waste lagoons on ground water quality as 13 CAFOs in the eastern two-thirds of Nebraska is complete. The investigation used the δ15N values of NH4-N and NO3-N as source indicators.A N-isotope response to different lagoon designs and management practices was apparent as the δ15N values in the lagoons, which ranged from +2.0%0 to 59.0%0. Results indicated that the anomalously low δ15N values at lagoon HB-3 were associated with continuous N-isotope dilution by the addition of fresh waste and short residence time in the lagoon. Its δ15N values in the lagoons, which ranged from +2.0%0 to +59.0%0. Results indicated that the anomalously low δ15N values at lagoon HB-3 were associated with continuous N-isotope dilution by the addition of fresh waste and short residence time in the lagoon. Its δ15N enrichment factor was -17.6. The anomalously high δ15N value (+59%0) at wastewater overflow lagoon at Wayne (HW-9-O) appears to result from volatilization during warm season when waste overflow ceases from the primary lagoon. The enrichment factor for the overflow lagoon was -15.4 and the primary lagoon was -35.9.In a newly constructed lagoon, δ15N values increased from +6.4%0 to +16.7%0 within a year and a half of operation. A strong correlation coefficient (r=0.97) between the δ15N of NH4-N and δ15N of TKN indicated that there is little isotopic fractionation in the ammonification of urea and other organic amines in the waste and / or the δ15N contribution from ammonia in much greater than that organic-N.The δ15N values of lagoon surface samples indicated that there was not a significant difference in δ15N values regardless of sampling location.During the warmer months, vertical stratification of the lagoon developed with the surface δ15N values being higher than those at the bottom. Ground water beneath ten of 13 CAFOs was not adversely impacted by lagoon leakage.NH4-N with enriched δ15N values occurred in downgradient shallow ground water at two CAGO lagoons.From a standpoint of soil texture and depth to ground water, these lagoons were constructed in highly vulnerable areas. Beneath three CAFOs, ground water DOC from lagoon leakage promoted in-situ biodenitrification and reduced downgradient NO3-N concentrations. The ground water quality beneath a decommissioned lagoon was severely contaminated by high NO3-N with enriched δ15N values leached from beneath the filled-in lagoon. Advisor:Roy F. Spaldin

Variability of Anaerobic Animal Waste Lagoon delta\u3csup\u3e15\u3c/sup\u3eN 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] \u3c5%)