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Lysimeter nest

Basin-scale assessment of transport of water and agricultural chemicals through the unsaturated zone. Rick Webb, Randy Bayless, Tracy Hancock, Chuck Fisher, Tom Nolan, Rick Healy, Jack Barbash, Josh Linard, and Mike Wieczorek. Lysimeter nest. Spatial Variability  Aquifer Vulnerability.

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Lysimeter nest

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  1. Basin-scale assessment of transport of water and agricultural chemicals through the unsaturated zone Rick Webb, Randy Bayless, Tracy Hancock, Chuck Fisher, Tom Nolan, Rick Healy, Jack Barbash, Josh Linard, and Mike Wieczorek

  2. Lysimeter nest Spatial Variability  Aquifer Vulnerability Recharge vector

  3. Objective • Develop a mobility index that classifies the potential leaching of agricultural chemicals to ground water. • The mobility is dependent on properties of the agricultural compounds and the soils • The leaching of mobile compounds to groundwater can be reduced by limiting applications before rainy months or in areas where the water table is near the surface.

  4. Leaching of nutrients and pesticides to groundwater are simulated with the following considerations. Agricultural practices (crop rotation and pesticides) Physical and chemical properties of compounds. Water Balance Soil properties Total leaching for source areas to wells or surface water are estimated as follows: Identify clusters or groups of similar soils and crops (and or rotations). Construct a mechanistic model for each major cluster and run stochastically for the range of soil characteristics properties unsaturated-zone thicknesses. Aerially weight the results to estimate mass fluxes for the Morgan Creek watershed. Final goal is to construct a mobility index specific to different hydroclimatic regions of the country. Approach

  5. Morgan Creek and Weather Stations

  6. Land Use 2004 Field Site

  7. Land Use Field Survey NLCDE Rural Forest Riparian & Wetlands Pasture/Hay Crops

  8. Land Use 2004 Field Site

  9. Stratigraphy and sampler locations

  10. Corn-Soy-Wheat crop rotations at the Maryland field site showing timing and loads of nutrients and herbicides 2 5 0 2 . 5 Explanation Fertilizers Crops Herbicides Atrazine Glyphosate Metolachlor Simazine Nitrogen Phosphorus Potassium Wheat Corn Soybeans 2 0 0 2 1 5 0 1 . 5 Crop height, in centimeters, or Nutrient load, in kilograms per hectare Herbicide load, in kilograms per hectare 1 0 0 1 5 0 0 . 5 Crop height, in centimeters, or Nutrient load in kilograms per hectare Herbicide load in kilograms per hectare 0 0 1 / 1 / 0 2 1 / 1 / 0 3 1 / 1 / 0 4 1 / 1 / 0 5

  11. Metolachlor – Immobile Metolachlor Ethane Sulfonic Acid (MESA) – Mobile Metolachlor Oxanilic Acid (MOXA) – Fairly immobile Pesticide properties Simazine Paraquat Diazonon Metolachlor 0.01 1.0 100 10,000 1,000,000 1.0 10 100 1000 3 5 7 9 10 10 10 10 10 Soil adsorption coefficient (Koc) Soil metabolism half-life, in days Solubility in water, in mg/L Potential groundwater risk Higher Lower

  12. Water balance

  13. Recharge

  14. Recharge and leaching greater where the unsaturated zone is less then 2.5 meters (12000 mm of precipitation) Recharge, in mm

  15. Leaching of nutrients and pesticides to groundwater are simulated with the following considerations. Agricultural practices (crop rotation and pesticides) Physical and chemical properties of compounds. Water Balance Soil properties Total leaching for source areas to wells or surface water are estimated as follows: Identify clusters or groups of similar soils and crops (and or rotations). Construct a mechanistic model for each major cluster and run stochastically for the range of soil characteristics properties unsaturated-zone thicknesses. Aerially weight the results to estimate mass fluxes for the Morgan Creek watershed. Final goal is to construct a mobility index specific to different hydroclimatic regions of the country. Approach (General)

  16. Grid sampling for crops, soils, and unsaturated zone thickness

  17. Central Nebraska PODL Metolachlor ESA (MESA) and Metolachlor OXA (MOXA) have longer half-lives than Metolachlor. MOXA is less mobile than MESA

  18. Metolachlor and metabolites in top 50cm Mass in horizon, in mg/m² Fraction of parent + metabolites

  19. 50cm – 100cm Mass in horizon, in mg/m² Fraction of parent + metabolites

  20. 100cm – 250cm Mass in horizon, in mg/m² Fraction of parent + metabolites

  21. 250cm – 1000cm Mass in horizon, in mg/m² Fraction of parent + metabolites

  22. Grid sampling for crops, soils, and unsaturated zone thickness

  23. Land Use Field Site

  24. Soil Texture andUnsaturated Zone Thickness Field Site

  25. Streams and wetlands Percent area thinner than value Unsaturated Zone thickness, in meters

  26. 180 160 MESA 140 MOXA 120 Metolachlor 100 80 60 40 20 0 0 2 4 6 8 10 12 Leached after four applications of Metolachlor at 140 mg/m² (1.4 kg/ha) over 10 years; Total applied = 5.6 kg/ha Leached to ground water, in mg/m² Depth of UZ, in meters

  27. Grid sampling for crops, soils, and unsaturated zone thickness

  28. Metolachlor Applied Residual Leached Transformed Units are kg/ha. Five applications of Metolachlor at 1.36 kg/ha = 6.8 kg/ha

  29. MESA Produced Leached Degraded Residual

  30. MOXA Produced Leached Residual Degraded

  31. Leaching of nutrients and pesticides to groundwater are simulated with the following considerations. Agricultural practices (crop rotation and pesticides) Physical and chemical properties of compounds. Water Balance Soil properties Total leaching for source areas to wells or surface water are estimated as follows: Identify clusters or groups of similar soils and crops (and or rotations). Construct a mechanistic model for each major cluster and run stochastically for the range of soil characteristics properties unsaturated-zone thicknesses. Aerially weight the results to estimate mass fluxes for the Morgan Creek watershed. Final goal is to construct a mobility index specific to different hydroclimatic regions of the country. Approach

  32. The soils beneath agricultural fields provide a complex chromatographic media that can enhance or impede the leaching of agricultural chemicals to ground water. The soil characteristics and thickness of the unsaturated zone define the properties of the chromatographic column; The climate and agricultural management practices determine the supply rate and residence time of the agricultural chemicals. Conjecture: The spatial and temporal variations of agricultural chemicals delivered to ground water may be reflected in the water pumped from the water-table aquifer. Conclusions

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