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Christina Siebe Institute of Geology National University of Mexico (UNAM)

R euse of untreated municipal wastewater for agriculture over a century at the Mezquital Valley, Mexico. Christina Siebe Institute of Geology National University of Mexico (UNAM). The Mezquital valley: >90,000 ha 40 m 3 s -1 untreated wastewater + 12 m 3 s -1 surface runoff

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Christina Siebe Institute of Geology National University of Mexico (UNAM)

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  1. Reuse of untreated municipal wastewater for agriculture over a century at the MezquitalValley, Mexico Christina Siebe Institute of Geology NationalUniversity of Mexico (UNAM)

  2. The Mezquital valley: • >90,000 ha • 40 m3 s-1 untreated wastewater • + 12 m3 s-1surface runoff • Overflow irrigation (1800-2200 mm) • Fodder crops and maize, mainly • Irrigation started 1912 and the area • has been growing continuously.

  3. Soilswithmediumtoveryhighfilter and buffer capacities: Rendzic/ mollic Leptosol Haplic/calcaricPhaeozem Pellic/eutric Vertisol

  4. “Long termexperiment” • Repeated sampling (1990 and 2009) of 21 to 24 fields irrigated for different lengths of time (0, 4, 8, 16, 30, 65 and 80 years). • SoilpropertiesCropquality: • Soilorganicmatter total biomass • Nutrientsnutrientcontents • Heavy metals heavy metal take up • Emergingpollutants Monitoring of selectedirrigationeventstofollow - leachingintogroundwater - greenhouse gas emissions

  5. Soil organic carbon Yearsunderirrigation

  6. Soil pH Yearsunderirrigation

  7. Total heavy metal contents in soil Yearsunderirrigation Yearsunderirrigation

  8. Heavy metal contents in alfalfa

  9. Antibioticconcentrations in soil Yearsunderirrigation

  10. Nitrogen balance Large N use efficiency (>85%), But, irrigationprovides more N thancrops can take up. Nitrateisleachingintotheaquifer Partial “self-cleaning” capacity of thesystemthroughdenitrificationin thevadosezone Small N2O emissionsintotheatmospheresomedaysafterirrigation

  11. Systemcomparisons: soil-aquifertreatment Lowcostwwtreatmentsystem Increaseyields of “low “ valuecrops (fodder, grains) Pathogens Excesswater, nutrients, salts Small doses of pollutants Increasesoilorganicmatter Accumulation of contaminants Groundwaterrecharge Nitrate and soluble saltleaching

  12. Treatedwastewater; dripirrigation Recovery? Investment and operationcosts Increasedproductivity of highcommercialvaluecrops Reducedhealthrisks Nutrientcontentsaccordingtoplantneeds…? Soluble salts? Largewater and nutrient use efficiency ¿Accumulation of soluble salts? Pollutantsaccumulate in sludges?

  13. Conclusions The Mezquital valley experience shows the long term effects of the use of untreated wastewater for irrigation (soil aquifer treatment). It also offers comparison with two alternative land use systems that use treated wastewater at several levels and with different irrigation technology. It serves for demonstration and training.

  14. Thankyou!

  15. Variación del error estándar

  16. Variación de la diferencia 2009-1990

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