iron and manganese key factors of NO3-N attenuation in shallow groundwater of the nitrogen attenuation

The key layers for NO3-N attenuation were the silty clay in the vadose zone and the water table fluctuation zone, with dissolved organic carbon (DOC) and Fe(II) as the predominant electron donors, respectively. Enzyme activity and microbial analysis corroborated that Fe(II) in the WTF zone was involved in NO3-N reduction. These findings underscore the significant role of Fe(II) in NO3-N reduction. Future studies could provide a basis for differentiated fertilizer nitrogen regulation by dividing the NAZ and exploring the nitrogen loading thresholds that the nitrogen attenuation capacity of different NAZ can endure.