Spatial distribution characteristics of dissolved n₂o in unconfi ned groundwater of an agricultural catchment affected by signifi cant fertilizer application

Spatial distribution characteristics of nitrous oxide (N²O) in an unconfi ned aquifer were examined, based on changes in concentrations of N²O, nitrate-nitrogen (NO^3--N) and other chemical components with the groundwater fl ow of an agricultural catchment affected by signifi cant fertilizer application. N²O concentrations were about 4μgN L^-1 in the upstream area, and were positively correlated with NO^3--N concentrations. These results suggest that the nitrifi cation process infl uences N²O concentrations in upstream areas. In the downstream area, N²O concentrations in deeper groundwater (> 15 m) were signifi cantly higher (13 μgN L^-1), but they were very low in shallower groundwater (< 15 m), below the detection limit. Spatial distributions of dissolved oxygen (DO) and dissolved organic carbon (DOC) suggest that shallower groundwater is characterized by a strong reducing condition and high organic carbon content compared to deeper groundwater. These results suggest that a complete denitrifi cation process (NO^3- → N²) occurs in shallower groundwater, whereas an incomplete denitrifi cation process causes the increase of N²O concentrations found in deeper groundwater.