Hydrologic pulsing has a considerable impact on both biogeochemical processes and microbial communities in wetlands. Since denitrifying bacteria play a key role regarding water quality improvement in wetlands, changes in their activities and communities related to hydrologic pulsing could be an important issue. Therefore, we investigated the responses of in situ denitrification rates (estimated by acetelyne reduction), denitrifying bacterial community structure and their quantities using nitrate reductase (nir) S gene under different hydrological pulsing conditions created by a short-term hydrologic drawdown and reflooding of 40 days duration in 1-ha created experimental wetlands at the Olentangy River Wetland Research Park in central Ohio.

Results/Conclusions Denitrification rates were significantly impacts by water depth. Average denitrification rates were 302, 133, 71 and 271 μg N₂O-N ·m^-2 ·hr^-1 during inundated, saturated, drying and reflooding periods, respectively. In contrast, the community structure based on terminal-restricted fragment length polymorphism (T-RFLP) analysis showed no significant change due to hydrologic pulsing. The nirS gene copy number remained relatively constant with only minor increases with water level drawdown and it deceased significantly when a sudden reflooding event occurred. These results indicate that environmental disturbances, such as hydrologic pulsing, have a dramatic impact on the denitrification process, but less of an effect on the community structure of the denitrifying bacteria. In addition, we found no relationship between denitrification and the community structure and quantity of denitrifiers, which suggests that the changes in denitrification rates during hydrologic pulsing events were not caused by the changes in community structure and quantity of denitrifiers, but rather directly by environmental conditions such as hydrology or substrate availability.