APPLICATION OF STABLE ISOTOPE ANALYSIS TO UNDERSTAND THE BEHAIVOR OF NITROGEN IN RECLAIMED WASTEWATER THROUGH THE SOIL COLUMN EXPERIMENT
Abstract:Reclaimed wastewater (RW) will be introduced for dry-farming on Okinawa Island, Japan in the near future. Nitrate (NO3 −) is a likely pollutant due to the irrigation of RW production on the island because RW contains about 18mg N/L of ammonium (NH4 +). In order to investigate the isotope effect on the belowground behavior of nitrogen contained in RW, nitrogen stable isotope analyses were conducted for the influent, effluent and soil of two laboratory soil columns and a field lysimeter, applied with RW as the influent. The relationships between the nitrogen stable isotope ratio (δ15N) and nitrogen behavior were evaluated. The NH4 +−δ15N and NO3 −–δ15N of influent and effluent of the two soil columns applied with RW continuously and intermittently, were measured. Both NH4 +–δ15N and NO3 −–δ15N increased during the percolation of RW through soil. There was a good relationship between NO3 −–δ15N and NO3 −concentration of the effluent. The results verified the nitrification of influent NH4 + and denitrification of NO3 −, especially the increase of denitrification in the continuous case (CC). The comparison of δ15N of initial and final soil at various depths of the two columns supported the increased denitrification in CC. The δ15N analysis of the percolated water from the lysimeter indicated that NO3 − originating from RW percolated through the soil. We conclude that the nitrogen stable isotope is a good indicator of the belowground behavior of nitrogen supplied by the RW irrigation.
Document Type: Research Article
Publication date: January 1, 2007
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