The drinking water of Izeh city in northeastern Khuzestan province is supplied from limestone wells in the Nal-e-asbi Karst aquifer south of the plain, which is in direct hydrogeological communication with the alluvial aquifer. Due to nitrate pollution infiltration from the alluvial aquifer to the Karst aquifer, determining the nitrate status in the aquifer and the effect of the natural denitrification process on reducing nitrate concentration is very important. In this research, temporal changes in nitrate, ammonium, and nitrite, and spatial changes in nitrate in the urban aquifer of Izeh were investigated to determine the denitrification mechanism. Over a one-year period (December 2023 - November 2024), samples were taken from 9 wells over 6 periods. Then, nitrate isoconcentration maps were prepared, and along with temporal changes of nitrogenous species, the nitrate chemograph was interpreted. Finally, spatial zoning of denitrification and the relationship between denitrification and other hydrogeochemical parameters was analyzed using composite diagrams. The results showed that with the leaching of pollutants from the surface and chemical fertilizers applied to agricultural lands, which are mainly applied in January and February in the Izeh region, the nitrate concentration in the urban aquifer of Izeh had a sharp increasing trend from December 2023 to April 2024, but decreased throughout the aquifer from April to June 2024. Groundwater in the north of Izeh city and adjacent to Miangaran wetland, due to severe contamination with Izeh city sewage, is under reducing and severe denitrification conditions and has the lowest nitrate concentration among the water wells. Based on the denitrification zoning map, the highest and lowest constant rate of denitrification are related to the northeast and southwest of Izeh city, respectively
