title: Does microbial centimeter-scale heterogeneity impact MCPA degradation in and leaching from a loamy agricultural soil?
abstract: The potential for pesticide degradation varies greatly at the centimeter-scale in agricultural soil. Three dimensional numerical simulations were conducted to evaluate how such small-scale spatial heterogeneity may affect the leaching of the biodegradable pesticide 2-methyl-4-chlorophenoxyacetic acid (MCPA) in the upper meter of a variably-saturated, loamy soil profile. To incorporate realistic spatial variation in degradation potential, we used data from a site where 420 mineralization curves over 5 depths have been measured. Monod kinetics was fitted to the individual curves to derive initial degrader biomass values, which were incorporated in a reactive transport model to simulate heterogeneous biodegradation. Six scenarios were set up using COMSOL Multiphysics to evaluate the difference between models having different degrader biomass distributions (homogeneous, heterogeneous, or no biomass) and either matrix flow or preferential flow through a soil matrix with a wormhole. MCPA leached, within 250 days, below 1m only when degrader biomass was absent and preferential flow occurred. Both biodegradation in the plow layer and the microbially active lining of the wormhole contributed to reducing MCPA-leaching below 1m. The spatial distribution of initial degrader biomass within each soil matrix layer, however, had little effect on the overall MCPA-leaching.
authors.affiliation: Geological Survey of Denmark and Greenland, Department of Geochemistry, Øster Voldgade 10, DK-1350 Copenhagen, Denmark. Electronic address: aer@geus.dk.
authors.forename: Annette E
authors.initials: AE
authors.lastname: Rosenbom
authors.affiliation: Technical University of Denmark, Department of Environmental Engineering, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Binning
authors.affiliation: Geological Survey of Denmark and Greenland, Department of Geochemistry, Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Aamand
authors.affiliation: Technical University of Denmark, Department of Environmental Engineering, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Dechesne
authors.affiliation: Technical University of Denmark, Department of Environmental Engineering, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Barth F
authors.initials: BF
authors.lastname: Smets
authors.affiliation: Geological Survey of Denmark and Greenland, Department of Geochemistry, Øster Voldgade 10, DK-1350 Copenhagen, Denmark.
authors.forename: Anders R
authors.initials: AR
authors.lastname: Johnsen
mesh_terms: D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000032:analysis / Q000378:metabolism*; D000383:Agriculture; D001673:Biodegradation, Environmental; D006540:Herbicides / Q000032:analysis / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000032:analysis / Q000378:metabolism*
chemical_list: D006540:Herbicides; D012987:Soil; D012989:Soil Pollutants; D008456:2-Methyl-4-chlorophenoxyacetic Acid
keywords: COMSOL simulations; MCPA leaching; Monod-kinetics; Preferential transport; Spatial biodegradation