Diatom aggregation when exposed to crude oil and chemical dispersant: Potential impacts of ocean acidification

Abstract

Diatoms play a key role in the marine carbon cycle with their high primary productivity and release of exudates such as extracellular polymeric substances (EPS) and transparent exopolymeric particles (TEP). These exudates contribute to aggregates (marine snow) that rapidly transport organic material to the seafloor, potentially capturing contaminants like petroleum components. Ocean acidification (OA) impacts marine organisms, especially those that utilize inorganic carbon for photosynthesis and EPS production. Here we investigated the response of the diatom Thalassiosira pseudonana grown to present day and future ocean conditions in the presence of a water accommodated fraction (WAF and OAWAF) of oil and a diluted chemically enhanced WAF (DCEWAF and OADCEWAF). T . pseudonana responded to WAF/DCEWAF but not OA and no multiplicative effect of the two factors (i.e., OA and oil/dispersant) was observed. T . pseudonana released more colloidal EPS (< 0.7 μm to > 3 kDa) in the presence of WAF/DCEWAF/OAWAF/OADCEWAF than in the corresponding Controls. Colloidal EPS and particulate EPS in the oil/dispersant treatments have higher protein-to-carbohydrate ratios than those in the control treatments, and thus are likely stickier and have a greater potential to form aggregates of marine oil snow. More TEP was produced in response to WAF than in Controls; OA did not influence its production. Polyaromatic hydrocarbon (PAH) concentrations and distributions were significantly impacted by the presence of dispersants but not OA. PAHs especially Phenanthrenes, Anthracenes, Chrysenes, Fluorenes, Fluoranthenes, Pyrenes, Dibenzothiophenes and 1-Methylphenanthrene show major variations in the aggregate and surrounding seawater fraction of oil and oil plus dispersant treatments. Studies like this add to the current knowledge of the combined effects of aggregation, marine snow formation, and the potential impacts of oil spills under ocean acidification scenarios.

Marine Snow Aggregates are Enriched in Polycyclic Aromatic Hydrocarbons (PAHs) in Oil Contaminated Waters: Insights from a Mesocosm Study

“…Particularly, the dispersion of oil and incorporation of the hydrocarbons into aggregates depends on the amphiphilic properties of the EPS [28,34,37,39]. Laboratory studies using roller-table systems were performed to investigate the formation of sinking marine snow using oil in water concentrations ranging from 600 to 10,000 µg/L [19,[40][41][42][43][44]. These experiments showed that sinking mucus webs, flocs, and oil aggregates were formed within 1 to 7 d of incubation.…”

Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers (ADDOMEx): Toward a Synthesis of Processes and Pathways of Marine Oil Snow Formation in Determining the Fate of Hydrocarbons

“…A comparison of PAH composition in MOS from laboratory roller table (Genzer et al, 2020) and mesocosm experiments [Bacosa et al, 2020;and GRIIDC dataset (10.7266/ER1EGZ8E)] with the PAH composition examined in the sediment samples of Gulf of Mexico (Romero et al, 2015), revealed interesting findings (Figure 5). Using non-metric multidimensional scaling (NMDS), the data points of both WAF and DCEWAF from roller table and mesocosm experiments clustered together with the sediment samples, suggesting some level of consistency in the PAHs that tend to remain in marine snow.…”

“…There has been considerable work done over many decades to determine parameterizations of sinking velocities of marine snow (Alldredge and Gotschalk, 1998;Iversen and Lampitt, 2020; Dibenz[a,h]anthracene, and Benzo[ghi]perylene were used for the analysis, with concentrations of each PAH normalized to percentage of total PAHs in each sample. More details on the PAH extraction, sample collection, field site and design of the roller table and mesocosm studies can be found in Genzer et al (2020); Bacosa et al (2020), Romero et al (2015) and GRIIDC dataset (10.7266/ER1EGZ8E). Laurenceau-Cornec et al, 2020;and the review by Silver, 2015).…”

“…Data points clustered to the right are sample from the original Deepwater Horizon (DWH) Macondo oil and the Day 1 sample from surrogate oil used in the laboratory mesocosm and roller table studies, whereas the points clustered largely to the left are marine snow samples from the field and laboratory experiments. Only PAHs such as Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz[a]anthracene, Chrysene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, and Benzo[ghi]perylene were used for the analysis, with concentrations of each PAH normalized to percentage of total PAHs in each sample.More details on the PAH extraction, sample collection, field site and design of the roller table and mesocosm studies can be found inGenzer et al (2020);Bacosa et al (2020),Romero et al (2015) and GRIIDC dataset (10.7266/ER1EGZ8E).…”

A Decade of GoMRI Dispersant Science: Lessons Learned and Recommendations for the Future

“…MOS formed in the presence of dispersant appeared to contain more n-alkanes than the oil-only aggregates (Fu et al, 2014;Genzer et al, 2020). EPSs trap oil droplets (see Figure 6 in Quigg et al, 2016) and increase the bioavailability of oil components to microbial communities (McGenity et al, 2012).…”