Denitrification rates and community structure of denitrifying bacteria in newly constructed wetland

Constructed wetlands are generally created for water quality amelioration using natural biogeochemical processes including denitrification. To have maximal denitrification rates in constructed wetlands, both optimal environmental conditions and activation of denitrifiers are required. In this study, we monitored temporal dynamics of the community structure of denitrifying bacteria by terminal restriction fragment length polymorphism (T-RFLP) in newly constructed wetlands over 2 growing seasons. We also measured denitrification rates and denitrifying enzyme activity (DEA) using an acetylene blocking method. Community structure of denitrifying bacteria differed between 2 years, and dominant T-RFs changed over the period. In addition, the composition of denitrifying bacteria became simplified in the second year. Along with changes in community structure of denitrifying bacteria, DEA increased substantially in the second year compared with that in the first year. This result suggests that several dominant and active denitrifiers may induce higher potential for denitrification as wetlands became stabilized. However, actual denitrification rates did not exhibit an annual difference, but were more strongly influenced by environmental conditions such as temperature, pH, and DOC concentrations. Overall results of this study indicate that active denitrifiers may dominate and denitrification potentials increase as a newly constructed wetland becomes stabilized, but actual denitrification rates are mainly constrained by environmental conditions such as temperature, pH and carbon availability.

Research highlights
► DEA (Denitrifying enzyme activity) increased substantially as a constructed wetland stabilized.
► This accompanies simplified community of denitrifiers, suggesting that dominant several species may play a key role in denitrification.
► However, actually denitrification rates were strongly affected by environmental conditions such as temperature, DOC and pH.