Effects of high nitrate input in the denitrification-DNRA activities in the sediment of a constructed wetland under varying C/N ratios

In constructed wetlands (CW), denitrification usually accounts for >60% of nitrogen removal and is supposedly affected by the inflow water and the wetland management practices. Fluctuations in nutrient concentration of inflow water can cause an impact in sediment properties and microbial communities living therein. We have estimated the effects of a high input of nitrate or nitrite (simulating an eutrophication event) on dissimilatory nitrite reduction by analysing the activities of nitrite reducing bacteria (denitrification and dissimilatory nitrite reduction to ammonia) at different C/N ratios in compartmentalized microcosms. Denitrification was always the predominant pathway for nitrite removal (>60%) and eventually led to the complete removal of nitrate. Dissimilatory nitrite reduction to ammonia was negatively affected by the input of nitrogen, and more severely due to a transient increase of nitrite. Analyses of the nir genes sequences based on DNA and cDNA analyses revealed the importance of uncultured phylotypes as main contributors to nitrite reduction in wetlands. Our results highlight a high recovery rate of the ecosystem service after a severe event of potential eutrophication and point to metabolic redundancy of denitrifiers.

Automated summary

This study found that denitrification is the primary pathway for nitrogen removal in constructed wetlands, with high inputs of nitrate or nitrite impacting sediment properties and microbial communities. Recovery of ecosystem services after eutrophication events was high, indicating metabolic redundancy of denitrifers.