In the spring of 2010, the MC 252 Deepwater Horizon well blow out lead to nearly five million barrels of Gulf of Mexico light sweet crude to be released into the northern Gulf at a depth of 1500 meters. Dispersant injected into the plume at the wellhead helped little to keep the oil below the surface. This dispersant inefficiency, coupled with the limited effectiveness of sea surface mitigation, allowed an estimated 150,000 barrels to impact the shores of the Northern Gulf of Mexico, from East Texas to the Western Florida Panhandle. Nearly half of the impacted coastline is comprised of permeable sandy beaches. The surface oil took several months to reach the shore, and over that time it was degraded by heat, UV light, oxygen, and microbes. The weathered oil final reached the shores of Pensacola Beach, Florida on June 22, 2010. In the surf zone, the weathered oil was mixed with sand to form Sediment-Oil-Aggregates (SOA) that sank in the swash zone between the beach and longshore bar. This SOA material was transported with longshore currents, and repeatedly buried and exhumed. The weathered oil also came ashore at the same time as Tropical Storm Lee, whose increased wave action cause some of the SOA material to be deposited and buried into the dry beach sediment above the high-water line. The goal of this dissertation is to investigate the fate of MC252 crude oil from the Deepwater Horizon accident on Northern Gulf of Mexico permeable sandy beaches. Sampling trips to Santa Rosa Island, Florida were performed monthly from July 2010 to July 2011, where sediment cores from the dry beach above the high-water line were taken. These cores were sectioned and incubated to measure microbial activity in response to the buried oil, using oxygen as a proxy, over the year after the oil came ashore. On these trips, SOA material on the beach and in the surf was collected, homogenized, and use for lab incubations to investigate the role of microbes, temperature, and mechanical stress due to wave action, on the degradation of SOA material in the surf zone. Column experiments were also performed to investigate the aerobic decomposition of SOA material in the coastal water column and permeable sediments. The time series incubations showed that clearly oiled sections of sediment had significantly higher oxygen consumption rates, compared to sections that were visibly clean. In October of 2010, beach cleaning crews used heavy machinery to exhume the top meter of beach, sieve out the large SOAs, and in the process homogenized the smaller oil particles throughout the top meter of beach sand, increasing the surface area available to microbes for degradation. By April of 2011, a clearly oiled layer in the beach was no longer visible. Along with decreasing visible oil in the dry sediment, SOA material in the swash zone also decreased during the year. In laboratory incubations, it was found that microbes play a large part in the degradation of the SOA material, with microbes accounting for 80% of the oxygen consumption in SOA incubations. Higher temperatures increased the rate of oxygen consumption, with warmer summer temperatures causing a 4-fold increase in oxygen consumption rates over winter temperatures. The mechanical stress of wave action also causes the SOA material to quickly fall apart. In incubations, SOA material was rotated at 0.5rpm, and SOAs were disintegrated within 24 hours. In column experiments, it was found that increased fluid front velocity increased the oxygen consumption rates of sediment with artificially weathered crude oil. In columns amended with SOA material, there was no difference in oxygen consumption compared to sediment with no SOA material. There was also very little DOC release in SOA columns where the water was amended with Corexit 9500®, suggesting that the small surface area to volume ratio of larger, intact SOAs buried in the sediment develop a tough crust of highly degraded hydrocarbons, protecting the more labile inside from microbial degradation. This research shows the importance of microbial activity, wave action, and temperature on the degradability of the Deepwater Horizon oil. The wave energy of the environment, coupled with the permeable sandy sediments and warm temperature of the Florida summer, all contributed to the rapid degradation of the oil. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2019. / April 12, 2019. / Beach, Corexit, Deepwater Horizon, Oil, SOA / Includes bibliographical references. / Markus Huettel, Professor Directing Dissertation; Thomas E. (Tom) Miller, University Representative; Jeffrey P. Chanton, Committee Member; William Dewar, Committee Member; Olivia Mason, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_709299 |
| Contributors | Kaba, John (author), Huettel, Markus (Professor Directing Dissertation), Miller, Thomas E. (University Representative), Chanton, Jeffrey P. (Committee Member), Dewar, William K. (Committee Member), Mason, Olivia Underwood (Committee Member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean and Atmospheric Science (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, doctoral thesis |
| Format | 1 online resource (87 pages), computer, application/pdf |
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