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Nitrogen Loss from Freshwater and Saline Estuarine Sediments¹

ABSTRACT

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.

Key Words: denitrification • nitrogen-15-1abeled ammonium-N • acetylene inhibition • nitrogen-15 balance

¹ Contribution from the Laboratory for Wetland Soils & Sediments, Center for Wetland Resources, Louisiana State University, Baton Rouge, LA 70803.

² Assistant Professor and Associte V, respectively, Louisiana State University.

Received for publication February 22, 1983.