Seasonal Variation in Populations of Nitrogen-Transforming Bacteria and Correlation with Nitrogen Removal in a Full-Scale Horizontal Flow Constructed Wetland Treating Polluted River Water

We investigated seasonal variations in the removal of NH4+, NO3−, and organic nitrogen from a full-scale horizontal subsurface flow constructed wetland located in Beijing, China, together with the species and number of associated bacteria. Urease activity, nitrifying enzymatic activity (NEA), and denitrifying enzymatic activity (DEA) were also analyzed in each season. The removal of NH4+, NO3−, and organic nitrogen varied seasonally, with higher values in summer and autumn. The bacterial species responsible for ammonification, nitrification, and denitrification also varied seasonally, with denitrifying bacteria changing the most and nitrifying bacteria changing the least. Bacterial numbers also changed seasonally, with higher numbers in the warm seasons (summer and autumn) and lower numbers in the cold seasons (spring and winter). Nitrogen transformation was more sensitive to urease, NEA, and DEA activity than to the number of bacteria. The activity levels of these enzymes were strongly correlated with the composition of the influent water, temperature, and the number of bacteria. The three enzymatic activities also correlated with each other. NEA and DEA were strongly correlated with temperature, suggesting that these enzymatic activities may be the limiting steps for removal of nitrogen in the cold seasons.