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Chiu Cheng

My primary research involves the investigation of solute flux in coastal, sandy habitats, with study sites primarily in the gulf coast of northern Florida at St. Joseph Peninsula State Park, bay side.  Specifically, my objectives are to quantify the flux of nutrients (NO2, NO3, PO4 and NH3) form the process of the ebullition of air bubbles that form as a result of photosynthesis.  In contrast to muddy, impermeable sediments that can trap large volumes of air in pockets and cracks before release, sandy environments allow for more exchange of pore water as the medium is less compact and not capable of trapping large volumes of gas.  From my preliminary lab experiments, the exchange of flourescein dye between the pore water and overlying water was observed to occur more quickly the shallower bubbles were released.  Closer to the sediment-water interface, bubbles were released more frequently, but were also smaller in volume compared to the ones released at slightly deeper depths at more-infrequent intervals.  The results suggest that ebullition may have a more significant impact on nutrient transport in environments conducive to these types of conditions of gas movement. 

These permeable sands dominate the coastal shelf and the numerous occurrence of free gas in surface sand layers should induce the transport of pore water.  Presumably, particulates such as nutrients, reduced metals and contaminants from the sediment are carried out into the water column, suggesting that ebullition may have an important biogeochemical role in the distribution of these nutrients.  Throughout the year, multiple deployments of 19-cm chambers will occur at St. Joseph Bay where an inert gas (nitrogen) will be pumped through the sediment in some of the chambers to compare differences between ebullition and diffusion.  Samples will be collected at designated time intervals for each of the 4 nutrients.  Br will be added as a tracer to measure the exchange of pore water and overlying water.  Additionally six 50-cm domes have been constructed to collect naturally-produced gas bubbles from the field to analyze for gas composition via a GC.   


Chiu on cruise