Effects of vegetation on ammonium removal and nitrous oxide emissions from pilot-scale drainage ditches

• The ditches vegetated with Pontederia cordata and Myriophyllum elatinoides increased NH4+-N removal rates by 50.8% and 71.4%, respectively.
• The ditches vegetated with Pontederia cordata and Myriophyllum elatinoides decreased N2O emissions by 68.3% and 70.4%, respectively.
• M. elatinoides was more effective than P. cordata at controlling N transport in drainage ditches.
• Vegetated drainage ditches (e.g., M. elatinoides) would be a simple treatment system for removing NH4+-N from agricultural runoff and reducing N2O emission.

Recently, vegetated drainage ditches have been used as one of the best management practices for controlling the transport of agricultural pollutants. In this study, a pilot-scale field experiment within a 135-km2 agricultural catchment was conducted to investigate the effectiveness of ditches vegetated with Pontederia cordata (Pontederia) and Myriophyllum elatinoides (Myriophyllum) and ditches without vegetation (Control) on ammonium (NH4+-N) removal and nitrous oxide (N2O) emissions. Compared to the control treatment, the ditches with both plant species (P. cordata and M. elatinoides) increased NH4+-N removal rates by 50.8% and 71.4% and decreased N2O emissions by 68.3% and 70.4% for NH4+-N loadings of 25 mg L−1 and 70 mg L−1, respectively. The linear mixed-effect model revealed that effluent NH4+-N concentrations were significantly decreased by 2.54% and 2.10% for each increase of one unit on sediment NH4+-N sorption and plant TN accumulations (p < 0.0001). The dominant NH4+-N removal pathways in Myriophyllum ditch were plant uptake and microbial nitrification-denitrification. However, in Pontederia and control ditches, NH4+-N was mainly removed by sediment sorption. These findings may suggest that vegetated drainage ditches (e.g., M. elatinoides) are capable of removing NH4+-N from agricultural runoff and can additionally reduce N2O emissions.