In addition, most studies of streams have focused on those with permanent flow while few studies have examined kinase inhibitors denitrification in ephemeral streams during times of continuous water flow. Thus, it is largely unknown how varying hydrologic regimes in agriculturally impacted streams and riparian buffer zones affect the denitrifying community and denitrification rates. Prior studies demonstrate that inundation of floodplains enhances denitrification in agriculturally impacted watersheds; such inundations occur frequently in tile-drain fed streams of the agricultural midwest. Moreover, restoration practices that promote riparian inundation can enhance floodplain denitrification and reduce N loads. Varied hydrologic and moisture regimes, such as drying and flooding, can alter nitrogen concentrations, ammonia diffusion, and oxygen concentrations. Water regime fluctuations can directly control duration of oxic and anoxic phases in soil, consequently affecting denitrification. Floods in riparian zones can result in pulses of denitrification and the magnitude of this response varies with flood duration. Soil moisture also impacts responses of denitrification to oxygen concentration and the pulse of denitrification post-flood can be sustained by addition of organic compounds. Many prior studies on denitrification have measured biogeochemical processes but have not considered the underlying bacterial community responsible for this process Varying moisture content and altered redox potential of seasonally flooded soil and sediment may alter both the community composition and function of the denitrifier community. In this study, we examined the effect of hydrologic regime on bacterial community composition and denitrification rates in agriculturally impacted streams. The inter-connection between bacterial community structure and function was also examined, as several studies suggest a relationship between rate of denitrification and denitrifier community composition. Exploration of such relationships is important because variation in denitrification potential may be related to properties of the denitrifier community. As environmental conditions become favorable to denitrification increased N removal by denitrification may occur because of: 1) increases in the rate of denitrification per cell and/or 2) changes in structure of the denitrifier community. For the latter possibility, the manifestation of these changes could be increases in number of denitrifiers or changes in composition of the denitrifier community. We predict that the physiological response will immediately follow flooding whereas changes in the structure of the denitrifier community will lag behind. Two agriculturally impacted streams in the Sugar Creek watershed in Indiana, USA were used as study sites and sampled periodically. The streams exhibit different hydrologic regimes; one stream is seasonally ephemeral because of its source, whereas the other stream has permanent flow throughout the year. Previous research on these streams, at times when both had flowing water, revealed significantly different denitrifier community composition and denitrification rates between streams. Additionally, a simulated flooding experiment was performed on the riparian benches of the ephemeral stream.