Washover events on coastal headland beaches occur when storm surge from cold fronts, high tides, tropical storms, and hurricanes move across the beach, reworking and depositing sand in the back marshes and shallow mudflat areas. On Fourchon Beach, Louisiana, a 9-mile coastal headland beach impacted by the Deep Water Horizon oil spill, these washover events have intermittently moved oil from the subtidal and intertidal portion of the beach to the supratidal mudflats and marsh areas. In order to determine the impacts of washover events on oil fate, 3 complementary studies were undertaken. First, washover areas (N=59) have been mapped and sampled for PAHs and n-alkanes in the most heavily impacted area at the eastern end of Fourchon Beach. Samples indicate the most heavily impacted segments were in areas where a physical breach of the beach developed. Second, characteristics of specific washover events and depth distribution were to establish typical categories of events (i.e., breaches, remobilization of oil on the beach and mobilization of subtidal oil mats) as well as the characteristics of oil mobilized by each category. Field measurements of washover event samples were analyzed by several weathering ratios including C30-hopane ratios, ÓPhenanthrene/ ÓChrysenes and ÓDibenzothiophene / ÓChrysenes double ratio plotting. Third, a laboratory microcosm study was conducted to understand the biogeochemical controls on oil biodegradation in the new environment (washover mudflat) and how these controls impact its ability to degrade naturally. The study used intact surface residue balls (SRBs) that were deposited on the beach and marsh from various washover events. Anaerobic and aerobic treatments consistent with the flooded mudflat areas were amended with nitrogen to determine if nutrients were limiting in the washover environment. Treatments were established for both crushed and intact SRBs. Results to date indicate that PAHs degrade optimally when the SRBs are crushed up and are placed under non-flooded conditions with C1-C4 phenanthrenes, C1-C3 dibenzothiophenes and C1-C2 chrysenes all showing a large decrease in concentration over 150 days. These studies were discussed in the context of remedial measures during the emergency response phase used on Fourchon Beach to prevent washover impacts.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-04142014-105844 |
| Date | 02 May 2014 |
| Creators | Curtis, David Nelson |
| Contributors | Pardue, John, Moe, William, Malone, Ronald |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-04142014-105844/ |
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