The laboratory experiment with amphipods suggested a similar effect to Bernhardt's field data. More food supplied as leaf discs apparently caused oxygen levels to drop, creating conditions favorable for denitrification, with consequent decrease in nitrate concentrations. Decreasing nitrate concentrations would be favorable for conditions downstream in the lake, where eutrophication from nitrates might otherwise occur. Oxygen concentrations were not dropped enough to increase mortality though, so as not to cause an undesirable side effect.
The laboratory experiment with amphipods done in 2008 using Oxyrase® showed that decreased oxygen levels caused decreased nitrate-N levels. Since experimental jars showed the greatest decrease in nitrate-N, then some of this decrease must be due to increased denitrification, as there is no apparent reason why decreased oxygen would lead to increased assimilation although Ambler et al.(2001) suggested lower levels of oxygen might be required for denitrication.
Ambler, Pelovitz, Ladd, and Steucek. 2001. A demonstration of nitrogen dynamics in oxic & hypoxic soils & sediments. The American Biology Teacher 63(3): 199-206.