Reactive transport of different dissolved organic nitrogen components in an unconfined aquifer

Dissolved organic nitrogen (DON) is often an overlooked form of nitrogen that can leach from the soil into aquifers. The reactive transport and dispersion of DON in aquifers can contribute to regional nitrogen contamination. The current body of research has primarily focused on the vertical leaching process of DON through the vadose zone. However, these studies have largely ignored the broader reactive transport of DON within aquifers under the influence of groundwater flow. In this study, we investigate the reactive transport of DON under groundwater flow conditions. Utilizing molecular biological technologies, we aim to reveal DON's intrinsic role in the nitrogen cycle within aquifers. Our findings reveal that urea exhibits greater mobility compared to amino acids and proteins. The transport of amino acids and proteins reduces the NO₃^--N concentrations (44.6 % and 89.6 %) compared to the blank control, while urea leads to the accumulation of NO₃^--N in groundwater (10.1 %). Amino acid and protein columns show higher relative abundances of Pseudomonas (10.1 % and 7.3 %) and Thermomonas (3.9 % and 5.1 %) with denitrification functions, facilitating denitrification in groundwater. Conversely, the presence of urea increases the relative abundances of Nitrosomonadaceae and Nitrophilus (0.33 % and 0.67 %), posing a potential NO₃^--N contamination risk. Biotransformation has the greatest effect on protein transport (19.6 %), while adsorption mainly influences amino acid transport (12.4 %). The study provides fundamental insights into the reactive transport of different DON components in aquifers, which holds important implications for regional groundwater environment protection.