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

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

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

Irrigated acreage 1,430 acres 13 fields ,730 acres 25 fields 2004

20 mi 30 km 0 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: in/yr Evaporation approximately: 30 in/yr N7 R8

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

Bulk density sampling Hydraulic conductivity & water retention sampling Soil coring

Soils Evidence of Macropores

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 ridge tillage - corn

N7 R8 Finger flowFunnel flow Results from Dye Tracing

Site R8 Macropores in Cores 7 – 12 in 24 – 30 in ft 50 ft

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

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

Water Quality Overall chemistry

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

1 7 1 W E

Kendall test for trend Nitrate-N Chloride

Nitrate-N Kendall Test for Trend

Chloride Kendall Test for Trend

Source Identification Nitrogen-15 Natural Abundance Method

 15 N (‰) = [( 15 N sample / 14 N standard air ) – 1] x 1000 Occurrence of Nitrogen Isotopes in air: 0.37 % 15 N % 14 N

Source Identification Nitrate-N Water Quality

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

Source Identification Soil Nitrogen Soil-Water Lysimeters

δ 15 N ‰ Values from sites R8 and N7 Extracted Total Inorganic N Extracted Ammonium Extracted Nitrate Soils Total Nitrogen (including organic)

Monitoring wells Spring 2006 Soils Site R8 Spring 2006

50 Soil Water Nitrate-N mg/L 150 Site N corn Dryland wheat/fallow 11 ‰ 8.5 ‰ 7.5 ‰ 19.8 ‰ Nitrate-N Site Y8 milo 9.3 ‰ 1.8 ‰ 9.5 ‰ Mid-Depth (ft) 50

Source Identification Plant Nitrogen

Wastewater Fertilizer only

Summary of Results 1) Yearly nitrate-N and chloride show an increasing trend at most of the monitoring wells ( ). 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)

Summary of Results (cont.) 6)  15 N 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 δ 15 N values

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)

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