Denitrification in estuarine sediments determined by membrane inlet mass spectrometry

Abstract

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. Denitrificafion was independent of salinity over the range of 1-13 ppt and was directly dependent on nitrate concentration over the range of O-200 μM in the overlying water. Denitrification was observed when the water-colunto nitrate concentration was <1 μM, 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 denitrificafion in this river can respond rapidly and directly to episodic events that cause changes in water-column nitrate concentration.