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Use of nitrogen-15 natural abundance method, other tracers, and water chemistry

Use of nitrogen-15 natural abundance method, other tracers, and water chemistry to evaluate movement of irrigated treated wastewater through loess soils, Dodge City, Kansas M.A. Townsend, M. A. Sophocleous, S. A. Macko, R.Ghijsen, M. Magnuson, and D. Schuette

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Use of nitrogen-15 natural abundance method, other tracers, and water chemistry

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  1. Use of nitrogen-15 natural abundance method, other tracers, and water chemistry to evaluate movement of irrigated treated wastewater through loess soils, Dodge City, Kansas M.A. Townsend, M. A. Sophocleous, S. A. Macko, R.Ghijsen, M. Magnuson, and D. Schuette NRCS Personnel: J. Warner, S. Graber, R. Still, T. Cochran; C. Watts NRCS Conference 2008

  2. Site description Evidence of macropores in soils Soil profiles of nitrate and chloride Water quality at site variability Nitrogen-15 isotope background Nitrogen-15 isotope results groundwater soils and lysimeters plants

  3. Wastewater Treatment Plant system schematic Dodge City packing plant collection station anaerobic digesters Waste water treatment facility aerobic treatment storage lagoons crop land

  4. Irrigated acreage 1987 1,430 acres 13 fields 2004 2,730 acres 25 fields

  5. R8 N7 20 mi 0 30 km 0 High Plains Aquifer Overlain by loess Soils are silt loams Macropores (indicated by dye tracing) permits preferential flow Depth to water ranges from 75 ft to 120+ ft Groundwater flow from west to east Rainfall approximately: 16-20 in/yr Evaporation approximately: 30 in/yr

  6. Deep soil monitoring Multi-level suction lysimeters and neutron access tube 5 – 12 ft 15-16 ft 30 – 50 ft 50 ft 50 ft

  7. Bulk density sampling Soil coring Hydraulic conductivity & water retention sampling

  8. Soils Evidence of Macropores

  9. ridgetillage- corn Minimum or no tillage practice • Minimum incorporation of pesticides and fertilizers to soil • Increased soluble chemicals in surface flow that can enter macropores • Plant residues on the surface and no tillage • enhance worm activity • allow worm holes and other macropore channels to stay open at the surface

  10. Finger flow Funnel flow N7 R8 Results from Dye Tracing

  11. 50 ft 29-30 ft Site R8 Macropores in Cores 7 – 12 in 24 – 30 in

  12. Site N7 Macropores in Cores 8 – 10 ft 12– 14 ft 10 – 10.5 ft

  13. Concentrations mg/kg and mg/L an μS/cm

  14. Water Quality Overall chemistry

  15. Water Quality Tracers Boron and Chloride Sulfate and Chloride Bromide/Chloride and Chloride

  16. 1 1 7 E W

  17. Kendall test for trend Nitrate-N Chloride

  18. Kendall Test for Trend Nitrate-N 1985-2005

  19. Kendall Test for Trend Chloride 1985-2005

  20. Source Identification Nitrogen-15 Natural Abundance Method

  21. Occurrence of Nitrogen Isotopes in air: 0.37 % 15N 99.63 % 14N 15N (‰) = [(15Nsample/14Nstandard air) – 1] x 1000

  22. Source Identification Nitrate-N Water Quality

  23. Animal Waste Volatilization Enrichment Denitrification Enrichment Fall 2007 Res Fall 06 Spring 06 Fall 2006 N7, 12 ft Res 7-05 R8, 15 ft Fall 05 Y8, 24 ft Fertilizer Y8, Irr

  24. Source Identification Soil Nitrogen Soil-Water Lysimeters

  25. Values from sites R8 and N7 Soils Total Nitrogen (including organic) Extracted Nitrate δ15N ‰ Extracted Total Inorganic N Extracted Ammonium

  26. Monitoring wells Spring 2006 Soils Site R8 Spring 2006

  27. Site Y8 Site R8 1986 Site N7 1998 0 12 ‰ corn corn 5.5 ‰ 6 2 milo 11 ‰ 12 4 9.3 ‰ 8.5 ‰ alfalfa 18 19.8 ‰ 6 7.5 ‰ 1.8 ‰ 24 8 Mid-Depth (ft) Mid-Depth (ft) 12 ‰ Dryland wheat/fallow corn 30 10 9.5 ‰ 36 12 42 14 2.4 ‰ 48 16 50 0 10 20 30 40 50 50 0 100 150 200 0 50 100 150 Nitrate-N Nitrate-N mg/kg Nitrate-N mg/L Soil Water Nitrate-N mg/L

  28. Source Identification Plant Nitrogen

  29. Wastewater Fertilizer only

  30. Summary of Results 1) Yearly nitrate-N and chloride show an increasing trend at most of the monitoring wells (1985-2005). 2) Decreasing trend of nitrate and chloride observed at edges of the irrigated fields suggesting possible dilution effects occurring over time 3) Boron, sulfate, and Br/Cl are good indicators of mixing of wastewater and ground water and evapoconcentration 4) Macropore flow impacts nitrate-N distribution in soil 5) Nitrogen-15 values support idea of macropore flow in the soils (higher lysimeter values than soil nitrogen)

  31. Summary of Results (cont.) 6) 15N values of ground water are different seasonally (fall versus spring) 7) Differences in values may be related to: a) recharge of fertilizer irrigation (pre-1986) increased wastewater application (post-1986) b) seasonal impacts of varying wastewater temperatures cold versus warm temperature impacts on bacterial nitrification rates 8) Plants utilize the wastewater as indicated by the δ15N values

  32. Acknowledgments KWRI: Funding source NRCS: J. Warner, S. Graber, R. Still, T. Cochran; C. Watts Servi-Tech: David Shuette; Fred Vocasek KSU-Extension: Fay Russett OMI (Dodge City): Peggy Pearman, Cliff Mastin Farm operator: Chuck Nicholson KGS: J. Healey, B. Engard, D. Thiele; J. Charlton Grad. students: Ashok KC (KGS current), Nick Schneider Amanda Feldt (KSU-Extension)

  33. Questions?

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