University of Arkansas, Fayetteville Division of Agriculture


Denitrification in metalimnetic water was examined under different conditions to determine how addition of nitrate (NO3 -) and particulate carbon (PC), aeration, and concentrations of nitrate affect denitrification. In the first experiment, water samples from a metalimnion were treated with different combinations of NO3 - and PC. Changes in excess N2 -N concentration for 10 days were measured using membrane inlet mass spectrometry (MIMS). The second experiment used the same treatments as the first experiment after aeration of water. Besides excess N2 -N concentrations, O2 concentrations were measured for 16 days. The third experiment examined how different initial concentrations of NO3 - influenced denitrification; and changes in the samples with the four different concentrations of NO3 - were measured using MIMS for 42 days. The first experiment indicated that all samples in this experiment had completed denitrification before this experiment, and denitrification occurred only in the samples added with NO3 -. An aeration event in the second experiment resulted in low initial excess N2 -N concentrations; and excess N2 -N concentrations increased most in the samples containing both PC and NO3 - and second most in PC amended samples. Excess N2 -N concentrations did not increase in other two treatments, indicating the effect of PC on creating anoxic conditions for denitrification. Differences in initial NO3 - concentrations did not result in differences in denitrification. This study showed denitrification in metalimnion can be enhanced by adding NO3 - and PC and by repeating oxic and anoxic condition of water, which can be a way to remove nitrogen from aquatic systems.