Denitrification in estuarine sediments determined by membrane inlet mass spectrometry
Limnology and Oceanography 43:334-339
Steady-state and transient-state denitrification rates were measured in sediment cores from a brackish river of the Chesapeake Bay using high-precision, membrane-inlet mass spectrometry. Denitrification was independent of salinity over the range of 1-13 ppt and was directly dependent on nitrate concentration over the range of 0-200 mu M in the overlying water. Denitrification was observed when the water-column nitrate concentration was <1 mu M, indicating that nitrification in the sediments was occurring. There was no detectable lag in the response of denitrification to an abrupt increase in nitrate in the overlying water column; moreover, the enhanced rate under nitrate enrichment was either stable or changed slowly over periods of days. Thus, the microbial flora remained poised to utilize increased nitrate supplies, suggesting that the denitrifiers were facultative. An analysis based on diffusion theory supports a view that denitrification was controlled by properties that affected the physical transport of nitrate from the water to the sites of denitrification. Our results indicate that denitrification in this river can respond rapidly and directly to episodic events that cause changes in water-column nitrate concentration.