Nitrogen Loss from Freshwater and Saline Estuarine Sediments1
- C. J. Smith and
- R. D. De Laune2
The magnitude of ammonium-N (NH4+-N) loss from nitrification-denitrification reactions in bottom sediments collected from saline and freshwater Louisiana Gulf Coast lakes was determined. Studies were conducted in the laboratory and field. Maximum gaseous N accumulation, from fresh-water and saline sediment amended with 4.5 µg nitrate-N (NO4−-N) g−1 (on dry-wt basis), was 1.6 and 1.4 µg N g−1, respectively. The addition of 50 µg NH4+-N g−1 stimulated the evolution of N2O from both sediments, and represents 0.02 and 0.2% of the NH4+-N applied to the saline and fresh sediment, respectively. Nitrous oxide (N2O) emissions measured in the field were low. The annual N2O emission was 10 and 34 mg N m−2 from the saline and freshwater lakes. These values agree closely with the N2O emission rates calculated from laboratory data.
Denitrification was also estimated from NH4+-N amended sediment using the acetylene (C2H2) inhibition technique and 15N balance. Recovery of 15N decreased rapidly during the 0- to 8-week period when high denitrification rates were measured. The denitrification rate estimated from 15N recovery during the 0- to 8-week period was 3.7 mg N m−2 d−2 for each sediment. Approximately 50% of the added 15N was lost, an amount equivalent to 1.4 g N m−2 y−1. As the added 15NH4+-N was incorporated into the organic N pool, little or no further 15N was lost.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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