Simultaneous Determination of Nitrification and Nitrate Reduction in Sediment-Water Columns by Nitrate-15 Dilution1
- R. D. DeLaune and
- C. J. Smith2
The magnitude of N loss from nitrification-denitrification reactions in sediment-water columns of a freshwater lake of Louisiana Gulf Coast drainage basin receiving elevated N loading from agricultural runoff was determining using 15NO3 dilution. Isotope dilution using added labeled NO3 allowed for the simultaneous determination of nitrification and NO3 reduction in the sediment-water column. The contribution of internal NH4 pools in bottom sediment to NO3 content in water column through diffusion and nitrification was measured. Nitrate reduction averaged 134 µmol m−2 h−1 over a 50-d incubation period in the sediment-water columns. Nitrification averaged 90 µmol m−2 h−1, approximately 70% of the denitrification rate. Nitrification and ammonium assimilation were also determined in lake water using 15N-labeled NH4 as a tracer. The nitrification rate determined in the water (0.9–1.4 mmol N m−3 d−1) was less than the rates measured in the sediment-water columns (1.4–3.3 mmol N m−3 d−1) using 15NO3 dilution. The results presented and isotope dilution technique used are applicable for use in understanding the fate of N in sediment-water systems of other aquatic environments.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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