DENITRIFICATION IN ESTUARINE SEDIMENTS DETERMINED BY MEMBRANE INLET MASS-SPECTROMETRY

Steady-state and transient-state denitrification rates were measured i n sediment cores from a brackish river of the Chesapeake Bay using hig h-precision, membrane-inlet mass spectrometry. Denitrification was ind ependent of salinity over the range of 1-13 ppt and was directly depen dent on nitrate concentration over the range of 0-200 mu M in the over lying water. Denitrification was observed when the water-column nitrat e concentration was <1 mu M, indicating that nitrification in the sedi ments was occurring. There was no detectable lag in the response of de nitrification to an abrupt increase in nitrate in the overlying water column; moreover, the enhanced rate under nitrate enrichment was eithe r stable or changed slowly over periods of days. Thus, the microbial f lora remained poised to utilize increased nitrate supplies, suggesting that the denitrifiers were facultative. An analysis based on diffusio n theory supports a view that denitrification was controlled by proper ties that affected the physical transport of nitrate from the water to the sites of denitrification. Our results indicate that denitrificati on in this river can respond rapidly and directly to episodic events t hat cause changes in water-column nitrate concentration.