Numerical simulation of herbicide transport and biogeochemical fate in the unsaturated zone of a lysimeter

B.Sc. Amr Abouamer, BSc

Master's thesis

Abstract:

This study discusses the contamination potential for groundwater of four herbicides and their metabolites, which was evaluated by numerical modeling of unsaturated flow and reactive transport using HYDRUS-1D. The herbicides were applied to a lysimeter vegetated with maize located in Wielenbach, Germany. The soil core of the weighable lysimeter contained a sandy gravel soil. Four models (the two models of the terbuthylazine and metolachlor branches with and without root water uptake) were set up to study the fate of the herbicides, simulating transport as well as biodegradation, metabolite production, sorption, and the influence of root water uptake. The considered herbicides were metolachlor, terbuthylazine, nicosulfuron, and porosulfuron., The formation of two metabolites was simulated for (metolachlor ethanesulfonic acid, MESA, and metolachlor oxanilic acid, MOXA), and four metabolites of terbuthylazine (desethyl-terbuthylazine, MT1, 2-hydroxy-terbuthylazine, MT13, terbuthylazine 2 CGA 324007, LM5, and terbuthylazine 1 SYN 545666, LM6). Concentrations of these compounds were monitored in lysimeter discharge. The reactive transport models have been set up based on available soil hydraulic parameters. Results of modeling were correlated with the measured data, and calibration of biodegradation and sorption parameters was done using PEST. Calibrated parameters of sorption, biodegradation, and percentages of produced metabolites ‘daughters’ agree well with literature findings. Consideration root water uptake did not show high differences compared to the approach without root water uptake. Observations could be described overall well by modeling, however, concentration peaks partly under- or overestimated sometimes three- to fivefold so that improvements are recommended in future studies.

Keywords

Agrochemical Pollution, Groundwater, HYDRUS-1D, Lysimeter, Maize, Metabolites, Modelling, Numerical Simulation, PEST, Pesticides, Unsaturated Zone, Vegetation

Language used: English

Date on which the thesis was submitted / produced: 1. 4. 2023

Thesis defence

• Date of defence: 16. 5. 2023
• Supervisor: doc. Mgr. Lukáš Trakal, Ph.D.
• Reader: Petr Ouředníček, Ing.

Czech University of Life Sciences Prague

Faculty of Environmental Sciences

Master programme:
Environmental Geosciences