Modelling assessment of carbon supply by different macrophytes for nitrogen removal in pilot vegetated mesocosms

The aim of this study was the evaluation of carbon supply by different macrophytes for nitrogen removal in constructed wetlands, using a dynamic numerical model previously developed by our work group to assess the results of a recently published meso-scale experiment. The experiment consisted of 12 mesocosms (five different macrophytes plus an unvegetated control, two cells each) drained once a week and immediately fed again until complete submersion with a solution of ammonium nitrate. To leave out any external carbon supply, no carbon substrate was added to the feed flux and no organic soil was included in the support media. The numerical simulations were obtained by calibration of the nitrification and denitrification processes driven by the alternate aerobic-anoxic phases generated by the weekly filling-emptying cycles. The carbon supplied by plants was demonstrated to be the main parameter affecting the denitrification rates observed in the experiments. It ranged in summer from 5.76 to 7.02 g/(m(2) d), while the control accounted for 5.11 g/(m(2) d). A winter test showed a 54% reduction of the summer supply of the same plant. The observed evapotranspiration rates were also simulated, and were shown to significantly affect the behaviour of the mesocosms planted with different species. Finally, the different vertical root-density distributions of the plants were found to play a relevant role in the development of nitrogen removal