Tsega Gsilassie, University of Maryland, Eastern Shore

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Abstract:

N₂, O₂ and Ar are the three most concentrated gases in aerobic waters. N₂ and O₂ are affected by both biological and physical processes, whereas Ar is affected strictly by physical processes. Deviation of these dissolved gases from equilibrium concentrations are common and reflect biological activates such as denitrification and photosynthesis acting on the system. These deviations also reflect the presence of physical processes such as bubble formation. Current methods for measuring denitrification sediments are hampered by bubble formation which can occur under illuminated conditions with an algal layer on the sediment surface. Bubbles stop N₂ and affect the relationship between concentration of N₂ and denitrification. The project investigates the processes of denitrification, photosynthesis and respiration by measuring the intensity of dissolved gases in samples using the membrane inlet mass spectrometer (MIMS). Sediment core samples were taken from the Choptank River and were setup in a temperature-controlled cylindrical chamber with 170ml of headwater. Test tube samples were taken from the headwater and run by mass spectrometer, water temperature, salinity, and depth profile were monitored to determine the relationship of these factors with the results of the experiment.
The experimental results show that the concentration dissolved O₂ levels kept increasing and dissolved N₂ has insignificantly fluctuated, supporting the fact that that denitrifying bacteria in the sediment core do not denitrify during the day. The research project has identified both advantages and disadvantages of the MIMS and provides a method to measure to investigate an overall system metabolism of a natural aquatic system.