Abstract:

The fate of crude oil components in eroding marsh substrates was examined by performing field measurements across a transect in a heavily oiled marsh in Bay Jimmy, Louisiana. Polycyclic aromatic hydrocarbon (PAHs) concentrations were measured in cores collected onshore, nearshore and offshore the marsh environment. The nearshore sample was just adjacent to the marsh edge (<1 m) in a shallow embayment while the offshore sample was located further into the bay (10 m) from the shoreline. Nutrient concentrations were measured in dialysis samples placed when the cores were taken and incubated for approximately 2 months. Microbial populations were measured using DNA extraction followed by Illumina Mi-Seq analysis followed by bioinformatics conducted using the Mothur protocol.

Suggested Citation:

Coronel, William, John H. Pardue, and Vijaikrishnah Elango. 2021. Fate of crude oil in eroding marsh substrates: field measurements. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/49WWTH44

Purpose:

The purpose of these measurements was to measure the differences in PAH concentrations, microbial populations and geochemical characteristics across a transect encompassing a rapidly eroding marsh shoreline.

Data Parameters and Units:

Date (yyy-mm-dd), Lat (latitude), Long (longitude), Sample Depth from surface (inch), Inverse Simpson Diversity Index, Non-metric Multidimentional Scaling, Average percent relative abundance of each core, PAH concentrations in soils/sediments (mg/kg), Nutrient concentrations in porewater (mg/L), Microbial abundance in samples (OTUs/gram), Depth below the surface (cm), Ammonia (mg-N/L), Nitrate (mg-N/L), Sulfate (mg/L), Phosphate (mg PO4/L).

Methods:

Core Sampling Three sets of sediment cores (10 cm diameter, 30 cm depth) were taken across transects of the marsh in the summer of 2017. Coring locations were recorded using Global Positioning System (GPS). The first set was taken on the marsh shoreline. The next two sets were taken 5’ and 20’ from the marsh shoreline. The sediment cores were brought back to the lab, sectioned, and stored at 3 °C prior to oil and DNA extraction. PAH Extraction and Analysis PAHs were extracted from sediment using Dionex Accelerated Solvent Extraction (Thermo Scientific). The sediment samples were homogenized and then subsampled for approximately 10 grams. The subsamples were mixed with diatomaceous earth for moisture removal and finally placed in a cell for extraction. The extractor pressurize and heats the cell containing the sample to 1700 PSI and 100 °C while extracting the oil constituents with 1:1 hexane and acetone as the solvents. The resulting extract of approximately 50 mL was then concentrated to 10 mL using a RapidVap N2 Dry Evaporation System (Labconco, USA). 1 mL of extract plus 5 µL of deuterated internal standard (naphthalene, acenapthylene, phenathrene, and chrysene) were added to a 1.5 mL Agilent vial. One µL from each vial was injected to Hewlett Packard 6890N gas chromatograph equipped with a HP series autosampler, DB 5 capillary column (30 m x 0.25 mm x 0.25 μm film), and 5973N mass selective detector. Helium was used as the carrier gas at a rate of 5.7 mL/min. The temperature program was as follows: injector 300°C, detector 280°C, oven temperature: 45°C for 3 min then increased at 6°C/min to 315°C and held for 15 min. For each set of samples, the QA/QC included adding blanks (1 mL hexane/acetone at 1:1 with 5 μL internal standard), using internal standard within each sample and running a calibration check sample. Weathering Ratios In order to analyze weathering trends for PAHs present, weathering ratios (WRs) are used. Weathering ratios (Equation 1 & 2) compare more readily degradable compounds to recalcitrant compounds where the 3-ringed PAHs phenanthrene and dibenzothiophene are compared to the 4-ringed chrysene. The WRs computed will be compared to a reference WR from crude oil collected at the surface of the DWH site (Diercks et al. 2010). Equation 1 PWR=((ΣPHEN))/((ΣPHEN+ΣCHRY) ) Equation 2 DWR= (( ΣDBZ))/((ΣDBZ+ΣCHRY) ) DNA Extraction and Analysis Bacterial community characterization for sediment samples was done by genomic DNA extraction using a PowerSoil DNA Isolation Kit® (MoBio Laboratories Inc.). Each sediment sample was homogenized and a 0.5 subsample was taken for genomic DNA extraction with a couple modifications to amplify the resulting extraction, (i) removing 200 μL of solution in the Powerbead tubes and adding 200 μL of phenol before adding the sample into the tube (ii) combining duplicate samples into one collection tube at the very end of extraction. DNA concentration as well as 260/230 and 260/280 purity ratios were measured using Thermo Scientific NanoDropTM spectrophotometer. After measuring the quality of the DNA extraction samples, samples were sent to Michigan State University for sequencing by PCR targeting the V4 region of the 16S rRNA gene on the Illumina Mi-Seq Platform. Sequenced data will be processed and analyzed using mothur v.1.34.4 (Kozich et al. 2013). The differences in bacterial population were shown quantitatively using non-metric multidimensional scaling (NMDS). Furthermore, analysis of molecular variance was done to compare bacterial populations. Nutrient Porewater Profiles Sampling of porewater was done at each of the three transects using 2.5’ long dialysis samplers constructed from plexiglass (Hesslein, 1976). Dialysis samplers have 70 cells filled with deionized water held by a HT-200 0.2 µm pore size membrane (Pall Corporation). This allows for diffusion sampling of water across the membrane. The samplers were inserted vertically at each transect and retrieved after approximately 2 months. However, the marsh and nearshore samplers were lost and only the offshore sampler was retrieved. During the retrieval process, water from the sampler cells was removed using a syringe, placed into 1.5 mL Agilent screw-top vials, and stored in a cooler with ice until laboratory analysis. In the lab, samples were stored no longer than 1 week at 3°C before analysis. A SmartChem 170 Discrete Analyzer (Unity Scientific Inc.) was used to measure ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), orthophosphates (PO43-), and sulfate (SO42-) concentrations using EPA methods #353.2, 353.3, 365.1, 350.1 and 375.4, respectively. QA/QC included blanks and 5-point calibration before every run.

Provenance and Historical References:

Diercks, Arne-R., Raymond C. Highsmith, Vernon L. Asper, DongJoo Joung, Zhengzhen Zhou, Laodong Guo, Alan M. Shiller, Samantha B. Joye, Andreas P. Teske, Norman Guinasso, Terry W. Wade, and Steven E. Lohrenz. 2010 Characterization of subsurface polycyclic aromatic hydrocarbons at the Deepwater Horizon site. Geophysical Research Letters 37(20): L20602. DOI:10.1029/2010GL045046. Hesslein, Raymond H. 1976. An in situ sampler for close interval for pore water studies. Limnology and Oceanography 21(6): 912-914. DOI: 10.4319/lo.1976.21.6.0912. Kozich James J., Sarah L. Westcott, Nielson T. Baxter, Sarah K. Highlander, and Patrick D. Schloss. 2013. Development of a dual-index sequencing strategy and curation pipeline for analyzing amplicon sequence data on the MiSeq Illumina sequencing platform. Applied Environmental Microbiology 79(17):5112–5120. DOI: 10.1128/AEM.01043-13.

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