Science Serving Maryland's Coasts

Jim Oldham, Hampshire College

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Direct Measurement of Metabolically Active Dissolved Gases, in Estuarine Waters and Sediments, Using Membrane Inlet Mass Spectrometry


Membrane inlet mass spectrometry has been employed in the study of a number of microbial processes in natural environments and proposed for other including denitrification. This paper proposes a methodology for studying metabolic activity in estuarine sediments and describes preliminary experiments designed to measure denitrification activity. N2:Ar rations were used to detect changes over time in N2 concentration in intact core samples and used to detect N2 disequilibria with depth in sediment pore waters. Denitrification was measured in a NO3- amended core in the first of three experiments but no denitrification was detected in subsequent experiments. These inconsistent results are attributed to probable variations in the microbial communities of the individual cores. Pore water samples showed a subsurface N2 peak, possibly a result of denitrification. There were also indications that physical processes may be contributing to disequilibria in sediment gas concentrations, making it difficult to draw conclusions about microbial activity.