Fate of herbicides in cropped lysimeters: 2. Leaching of four maize herbicides considering different processes

Abstract This study investigates the contamination potential of herbicides to groundwater with help numerical modeling (HYDRUS‐1D) and stable carbon isotopes for characterizing biodegradation. Four herbicides, metolachlor, terbuthylazine, prosulfuron, nicosulfuron, were applied over a period 4.5 years on two lysimeters located in Wielenbach, Germany, monitored by lysimeter drainage. These contained soil cores dominated sandy gravel (Ly1) clayey silt (Ly2) both cropped maize ( Zea mays ). In preceding study, we characterized flow within using water unsaturated models. Building up these findings, models extended describing reactive transport investigating process contributions. At end experiment, 0.9%–15.9% (up 20.9% if including metabolites) recovered Metabolite formation accumulation was observed, biodegradation also indicated small changes isotope signals (δ 13 C) between leached herbicides. Model setups could describe dynamics herbicide concentrations drainage well. Concentration peaks partly linked strong precipitation events, indicating preferential influence. The core coarser texture showed less leaching than finer (Ly2), which can be explained larger mobile phase Ly1. Overall, our approaches findings contribute understanding multi‐process vadose zone potentials groundwater, where δ C provide valuable hints microbial degradation.