Morales-McDevitt, Maya Erin (2017-05). Enriched Mesocosm Experiments to Study the Production of Marine Oil Snow in the Presence of BP Surrogate Oil and Corexit 9500A. Master's Thesis.
Thesis
During the Deepwater Horizon (DWH) oil spill, profuse marine snow with associated oil, termed marine oil snow (MOS) was observed but quickly disappeared. This research tested the hypothesis that in water with nutrients and microbes MOS formed in the presence of oil and oil plus dispersant. Four mesocosm experiments were undertaken as part of the ADDOMEx Consortium. Water was collected from near-shore (mesocosom 1, 2 and 4) or off-shore (mesocosm 3) in the Gulf of Mexico. Oil (Macondo surrogate oil) and oil plus dispersant (using Corexit 9500) mixtures known as water accommodated fraction (WAF), chemically enhanced water accommodated fraction (CEWAF) were generated in specially designed 170 L baffled recirculation tanks. WAF and CEWAF were then transferred to 106 L mesocosm tanks for the experiment as well as mesocosm control tanks (sea water only) and 10 times diluted CEWAF (DCEWAF) mesocosm tanks. Concentrated phytoplankton were added to mesocosm experiment 1 and 2. Nutrients were added to mesocosum 3 and 4. Estimated oil equivalents (EOE), Total petroleum hydrocarbons (TPH), including n-alkanes and pristine and phytane, NO3-, NO2-, NH4 and HPO4 concentrations of mesocosms were measured over time. Exopolyomeric substances formed within 24 hrs in all treatments including the controls. EOE concentrations decreased at similar rates in all treatments. Oil components were removed by formation and then sedimentation of MOS. Preferential removal of normal alkanes compared to branched alkanes (isoprenoid hydrocarbons) show that biodegradation was also occurring. Study results document that concentrations decreased partially due to sedimentation and biodegradation, although other weathering processes such as evaporation and photo-oxidation may also be responsible for the decrease in hydrocarbons in the mesocosms oil. Correlation between decrease in concentrations of EOE and nutrients indicate growth of microbes is important to MOS formation. The use of mesocosm studies provide a useful tool in understanding the mechanisms of MOS formation and transfer of oil from the water column to sediments.
