A measurement technique of the denitrifier method

which was developed for seawater isotopic analysis

was established for analyzing nitrogen isotopic composition of nitrate in groundwater and the vadose zone sediments.Experiments were conducted using international isotopic standards of IAEA-N3 and USGS34 and field samples.δ15N analyses of the two isotopic standards showed good reproducibility

with an average precision of 0.25‰(ranging from 0.1‰ to 0.5‰).Groundwater and sediment extracts were accurately reproduced

with precisions of better 0.5‰.The results showed that the measurement technique of the denitrifier method could be used for analyzing nitrogen isotopic composition of nitrate in groundwater and sediments.A case study using the technique showed that a thick vadose zone sediment profile had no increase trend of δ 15N values in depths below the vadose zone

indicating little denitrification occurrence.