Semester of Graduation

Spring 2020

Degree

Master of Civil Engineering (MCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

Marshes impacted by the Macondo spill continue to erode, releasing crude oil in the form of a soft asphalt or emulsion to adjacent shallow embayments. This process moves highly weathered crude oil from the marsh profile to comparatively high-energy, shallow, open-water systems where geochemical and microbiological conditions may influence additional weathering. Specifically, we hypothesize that the erosion process can accelerate biodegradation by moving crude oil asphalts and emulsions from a low-energy, anoxic environment in the marsh to a higher-energy, oxic environment in these shallow embayments. Sediment samples were taken in summer 2017 and 2018 across transects which bisect the boundary between a contaminated marsh and Barataria Basin, in the vicinity of Bay Jimmy/Bay Batiste where significant oiling occurred on the marsh surface. Samples were analyzed by GC-MS and weathering ratios constructed from 2 and 3-ring PAH compound series (C1-, C2-, C3- and C4-, alkylated phenanthrenes and dibenzothiophenes) compared with 4-ring PAH series, computed from C1-, C2 and C3-chrysene data. Bacterial populations were assessed using Ilumina sequencing using MiSeq protocols and non-matrix dimensional scaling to compare microbial community structure. In addition, microbial data was mined for the abundance of sequences associated with known PAH degraders from genera such as Halomonas and Marinobacter, previously identified on the marsh surface. Dialysis samplers, placed along the same offshore transect, measured nutrients, N and P, and redox indicators like sulfate. Results indicate that secondary deposition of crude oil derived PAHs is not occurring uniformly across these embayments. A defined oil layer was absent from offshore cores. Relative PAH weathering, microbial community structure and porewater geochemistry are discussed to draw conclusions on ongoing weathering of Macondo oil in these systems.

Committee Chair

Pardue, John

DOI

10.31390/gradschool_theses.5048

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