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GASIR2023

27-29 September 2023, University of Bayreuth (UBT)

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Characterization of pesticide fate in the unsaturated zone using numerical transport modeling and stable carbon isotopes

Anne Imig1, Lea Augustin1, Jannis Groh2, Thomas Pütz3, Martin Elsner4, Florian Einsiedl1, Arno Rein1
1 Chair of Hydrogeology, Technical University of Munich
2 Institute of Crop Science and Resource Conservation – Soil Science and Soil Ecology, University of Bonn, Bonn, Germany; Institute of Bio- and Geoscience (IBG-3, Agrosphere), Forschungszentrum Jülich GmbH, Jülich, Germany; Research Area 1 “Landscape Functioning”, Working Group “Hydropedology”, Leibniz Centre for Agricultural Landscape Research (ZALF), Müncheberg, Germany
3 Institute of Bio- and Geoscience (IBG-3, Agrosphere), Forschungszentrum Jülich GmbH, Jülich, Germany
4 Chair of Analytical Chemistry and Water Chemistry, Faculty of Chemistry, Technical University of Munich

O 4.1 in Environment and Pollution

28.09.2023, 15:30-15:45, H 36

Agrochemicals including nitrate and pesticides pose threats to ecosystems and groundwater. A field study was conducted at two lysimeters located in Wielenbach, Germany, with different soil textures within the soil cores (sandy gravel and clayey sandy silt). The lysimeters were vegetated with maize, and four different herbicides were applied according to common agricultural practice. Over a period of 4.5 years, concentrations of the herbicides and some of their metabolites were monitored in lysimeter discharge. Stable carbon isotopes (δ13C) were analyzed for investigating biodegradation influences. Numerical modeling with HYDRUS-1D was carried out for describing unsaturated flow and reactive transport of the herbicides, and simulations were interpreted in combination with measured δ13C. 

At the end of the observations, 0.9 to 15.9% of the applied herbicides (up to 20.9% for herbicides plus metabolites) were recovered in lysimeter drainage. Metabolites were observed to accumulate, and biodegradation was indicated by small changes in δ13C between applied herbicide solution and leached herbicides. Results point towards a higher biodegradation activity when infiltrated (herbicide-contaminated) water was residing a longer time in the unsaturated zone. Herbicide dynamics in lysimeter discharge could be covered well by modeling. Compound-specific isotope analysis using δ13C provided valuable hints for microbial degradation of herbicides in the unsaturated zone.



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