Biodegradation of MC252 oil in oil:sand aggregates in a coastal headland beach environment

Abstract

Unique oil:sand aggregates, termed surface residue balls (SRBs), were formed on coastal headland beaches along the northern Gulf of Mexico as emulsified MC252 crude oil mixed with sand following the Deepwater Horizon spill event. The objective of this study is to assess the biodegradation potential of crude oil components in these aggregates using multiple lines of evidence on a heavily-impacted coastal headland beach in Louisiana, USA. SRBs were sampled over a 19-month period on the supratidal beach environment with reasonable control over and knowledge of the residence time of the aggregates on the beach surface. Polycyclic aromatic hydrocarbons (PAHs) and alkane concentration ratios were measured including PAH/C30-hopane, C2/C3 phenanthrenes, C2/C3 dibenzothiophenes and alkane/C30-hopane and demonstrated that biodegradation was occurring in SRBs in the supratidal. These biodegradation reactions occurred over time frames relevant to the coastal processes moving SRBs off the beach. In contrast, submerged oil mat samples from the intertidal did not demonstrate chemical changes consistent with biodegradation. Review and analysis of additional biogeochemical parameters suggested the existence of a moisture and nutrient-limited biodegradation regime on the supratidal beach environment. At this location, SRBs possess moisture contents <2% and molar C:N ratios from 131–323, well outside of optimal values for biodegradation in the literature. Despite these limitations, biodegradation of PAHs and alkanes proceeded at relevant rates (2–8 year−1) due in part to the presence of degrading populations, i.e., Mycobacterium sp., adapted to these conditions. For submerged oil mat samples in the intertidal, an oxygen and salinity-impacted regime is proposed that severely limits biodegradation of alkanes and PAHs in this environment. These results support the hypothesis that SRBs deposited at different locations on the beach have different biogeochemical characteristics (e.g., moisture, salinity, terminal electron acceptors, nutrient, and oil composition) due, in part, to their location on the landscape.

Input of organic matter enhances degradation of weathered diesel fuel in sub-tropical sediments

“…Following the 2010 Deep Water Horizon (DWH) oil spill in the northern Gulf of Mexico, the restoration of coastal ecosystems has focused national attention on the importance of these vital ecological locales (Allan et al, 2012;Lin and Mendelssohn, 2012;Mortazavi et al, 2013a). Although reports following the DWH spill indicated that natural attenuation processes were occurring at many sites (Allan et al, 2012;Beazley et al, 2012), weathered oil may remain trapped in the area sediments, posing potential long-term risks to the environment (Allan et al, 2012;Lemelle et al, 2014;Elango et al, 2014).…”

Potential Environmental Factors Affecting Oil-Degrading Bacterial Populations in Deep and Surface Waters of the Northern Gulf of Mexico

“…For example, nitrate and phosphate are enriched in deep water, but depleted in surface water. Inorganic nutrients are often a limiting factor during hydrocarbon degradation in natural environments, and may regulate the development of oil-degrading bacterial communities (Edwards et al, 2011; Dubinsky et al, 2013; Elango et al, 2014). Ambient bacterial community may also be important as oil encounters different communities during the transit from deep to surface ocean.…”

Formation, Fate, and Impacts of Microscopic and Macroscopic Oil‐Sediment Residues in Nearshore Marine Environments: A Critical Review

“…Due to the magnitude of SOA and SOM contamination along the northern Gulf coast following the Deepwater Horizon spill, several studies have been carried out to understand the distribution, transport dynamics, and physical and chemical characteristics of these agglomerates, most notably in Louisiana (Elango et al, ; Lemelle et al, ; Urbano et al, ), Alabama (Clement et al, ; Hayworth et al, ; Wang & Roberts, ; Yin et al, ), and some in Florida (Wang & Roberts, ). SOAs resulting from this spill were typically found on the range of 0.5–8 cm in diameter, while SOMs spanned up to several meters in length and were up to 20 cm thick (Dickey & Huettel, ; Hayworth et al, ; Michel et al, ).…”

“…Typically, the oil that forms SOAs and SOMs undergoes significant weathering prior to reaching the shoreline, in some cases losing up to 50–60% of its mass including many alkanes and PAHs (Liu et al, ; Stout et al, ). Therefore, the oil that is derived from macroscopic agglomerates will always show reductions in alkanes, saturates, and PAHs compared to fresh oil; however, the reductions in the rate of degradation of these compounds once they are trapped in SOAs and SOMs have been a major concern (Elango et al, ; Evans et al, ; Gros et al, ; John et al, ; Stout et al, ; Urbano et al, ; Yin et al, ).…”