Experimental microcosm study of the effects of Deepwater Horizon MC-252 oil on the geochemistry and microbiology of Gulf Coast sediment
Abstract
Microcosm experiments were conducted to examine the impact of oil contamination on Gulf Coast sediment geochemistry and microbial population dynamics. Coastal sediment and seawater were collected from a salt marsh at Bayou la Batre, Alabama, which was not severely impacted by the BP Deepwater Horizon accident of April 2010. Sediment/seawater microcosms were set up in glass jars combusted for 5 hours at 450 degrees C. Non-sterile microcosms spiked with 500 ppm of MC-252 oil were sacrificed in duplicate at various time intervals over a 14 day period to establish a data time series. Sterile controls with and without oil and a non-sterile control without oil were sacrificed in duplicate at 14 days for comparison with the time-series experiments. Solid and aqueous phases were separated by centrifugation and prepared for analysis. Sediment mineralogy was determined using X-ray diffraction and acid-extractable sediment chemistry determined using EPA Method 3051A and ICP-OES analysis. The aqueous phase chemistry was analyzed by ICP-OES and ion chromatography. The mineralogy of the salt marsh sediment is predominantly quartz, but includes reactive phases such as clays (smectite, illite), feldspar, and iron oxide. Iron-bearing clays and iron oxides can serve as electron acceptors for the growth of Fe(III)-reducing bacteria. Microwave digestions of the microcosm substrate samples were performed in triplicate and show no significant variation in major element chemistry over the course of the two week experiment, suggesting that observed temporal trends in aqueous geochemistry may be due to ion exchange processes, rather than mineral dissolution reactions. Microcosm substrate trace element data which indicate possible differences with time are being analyzed for statistical significance. Analysis of aqueous solution geochemistry reveals several interesting temporal trends. Iron and manganese were released to solution after 2 days, suggesting the presence of facultative anaerobic bacteria which are utilizing iron-bearing minerals in the sediment as an electron receptor. Analysis of the bacterial communities present in the experimental substrates is ongoing. Preliminary results using PCR amplification of biodegradative genes relevant to the crude oil show that the 14 day oil-contaminated substrate exhibits positive detection of alkene hydroxylase (alkB), catechol 2,3-dioxygenase (C23DO) and biophenyl dioxygenase (bph) genes. Positive amplification of the bph gene in the uncontaminated non-sterile control confirms that hydrocarbon-degrading microorganisms naturally exist in the sediment. Bacterial tag-encoded FLX-titanium amplicon pyrosequencing is underway to evaluate microbial diversity and function, and is expected to explain observed trends in iron, manganese and trace element geochemistry. Microbial diversity analysis will also include taxonomic and biochemical characterization of bacterial isolates plated on 0.5 Marine Agar and 0.5 R2A and minimal media with MC-252 oil.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B13E0626D
- Keywords:
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- 0448 BIOGEOSCIENCES / Geomicrobiology;
- 0463 BIOGEOSCIENCES / Microbe/mineral interactions;
- 0465 BIOGEOSCIENCES / Microbiology: ecology;
- physiology and genomics;
- 0478 BIOGEOSCIENCES / Pollution: urban;
- regional and global