Due to their small particle size and wide distribution, microplastics can be incorporated into the biogeochemical pathways and food webs of the marine water column and sediment. Our understanding of microplastics in these pathways is still nascent, but of fundamental importance to estimate plastic's environmental fate and potential remediation. A massive research effort across fields in the last years has brought our understanding further, but there is a strong need to streamline and converge findings. Here, we discuss evidence from controlled laboratory experiments and field studies on microbe-plastic interactions and consider the biogeochemical relevance. Particular focus is on new methods and analytical approaches to understand the two-way interactions between microorganisms and microplastics and the implications for the environmental fate of marine plastic litter. AbstractMicroorganisms drive the biogeochemical cycles that link abiotic and biotic processes in the aqueous environment and are intricately associated with plastic debris. The presence of microplastics in water and sediment introduces new concerns as small particle size allows for increased pathways of microplastics in the food web and element cycles. In this review, we present the current state of knowledge on microbe-plastic interactions and summarize the potential impact of biogeochemical processes on plastic distribution, cycling, transport, and sedimentation. We explore how microbe-plastic interactions influence the exposure of consumers to microplastics and plastic degradation products. Key methods used to elucidate biofilm development, microbial biodegradation, and microplastic detection in the aqueous environment are discussed. Finally, we comment on potential future questions and research directions needed to further define the role of microorganisms in the environmental fate of microplastics.
In contrast to other oligotrophic water bodies the Gulf of Mexico (GOM) hosts an abundance of hydrocarbon seeps, which likely influences the microbial assemblages it hosts particularly regarding the availability of labile carbon in the aphotic GOM. The aphotic zone receives direct injection of seep methane (CH 4 ), but CH 4 from an unknown source has been reported at supersaturated concentrations relative to the atmosphere in the GOM photic zone. Here we used iTag sequencing of 16S rRNA genes to characterize GOM microbial communities and to relate changes in microbial community structure to the properties inherent to their oceanic province-seafloor to the photic zone, seep and non-seep. Along this trajectory water column communities were distinct in the euphotic zone compared to the mesopelagic and deep-sea. In the euphotic zone the relative abundance of a cyanobacterial species (Prochlorococcus) was significantly correlated with both CH 4 and chlorophyll a concentrations and was abundant in some deep-chlorophyll maximum (DCM) samples. The relative abundance of microorganisms related to known hydrocarbon degraders were also significantly correlated with CH 4 in the euphotic zone, but no canonical methanotrophs were observed. In the mesopelagic to the seafloor canonical methanotrophs were identified, but only a Marine Group II Euryarchaeota was significantly correlated with CH 4 . Overall, depth and the associated environmental conditions were the primary drivers in structuring microbial communities over the GOM water column. Further, CH 4 concentrations and relative microbial abundances covaried significantly from the seafloor to the photic zone in the GOM. The lack of a significant relationship between canonical methanotrophs and CH 4 in the aphotic zone, even when sampling at seep sites, may suggest methane-oxidation by unknown microorganisms. Similarly their absence in the CH 4 maximum and DCM suggested that CH 4 is either oxidized by unrecognized methanotrophs or escapes the CH 4 biofilter and fluxes to the atmosphere.
The Deep Water Horizon (DWH) incident caused the release of an unprecedented amount of 13C‐ and 14C‐depleted oil and gas to the Gulf of Mexico (GoM), which formed surface slicks and deep oil/gas plumes that extended laterally at 1000–1200 m. We conducted three research cruises between 2010 and 2012 to study the potential assimilation of petrocarbon (C derived from oil and/or gas) into the GoM microbial food web. In 2010, we found low δ13C (−30 to −25‰) and Δ14C (−603 to −55‰) values for suspended particles at 1000–1200 m depth as far as 289 km SW of the wellhead, providing direct evidence of the spatial extent of the subsurface plumes. At those depths in 2010, methane and oil carbon accounted for up to 28% and 62% of total particulate carbon (Csp), respectively. In the total area affected by the DWH, 80 ± 56 to 104 ± 91 tonnes (t) of methane‐derived and 216 ± 174 to 292 ± 165 t of oil‐derived carbon were incorporated into Csp. In 2011 and 2012, the δ13C values were distributed throughout the water column indicating that petrocarbon was still present and recycling, especially in the section closest to the DWH, where oil supplied up to 53% and 75% of Csp, respectively. Relatively low δ15N (< 4‰) values in suspended particles at 1000–1200 m in 2010 indicate stimulation of nitrogen fixation linked to methane oxidation in the months after the spill, which accounted for up to 40% of the particulate nitrogen in the water column at those depths.
The extensive release of oil during the 2010 Deepwater Horizon spill in the northern Gulf of Mexico perturbed the pelagic ecosystem and associated sinking material. To gauge the recovery and post-spill baseline sources, we measured D We interpret this depletion period, also observed in d 13C data, as caused by the incorporation of naturally seeped oil into sinking particles. Determination of post-spill baselines for these isotopic signatures allows for evaluation of anthropogenic inputs in future.
Hydrocarbons released during the Deepwater Horizon (DWH) oil spill weathered due to exposure to oxygen, light, and microbes. During weathering, the hydrocarbons’ reactivity and lability was altered, but it remained identifiable as “petrocarbon” due to its retention of the distinctive isotope signatures ( 14 C and 13 C) of petroleum. Relative to the initial estimates of the quantity of oil-residue deposited in Gulf sediments based on 2010–2011 data, the overall coverage and quantity of the fossil carbon on the seafloor has been attenuated. To analyze recovery of oil contaminated deep-sea sediments in the northern Gulf of Mexico we tracked the carbon isotopic composition ( 13 C and 14 C, radiocarbon) of bulk sedimentary organic carbon through time at 4 sites. Using ramped pyrolysis/oxidation, we determined the thermochemical stability of sediment organic matter at 5 sites, two of these in time series. There were clear differences between crude oil (which decomposed at a lower temperature during ramped oxidation), natural hydrocarbon seep sediment (decomposing at a higher temperature; Δ 14 C = -912‰) and our control site (decomposing at a moderate temperature; Δ 14 C = -189‰), in both the stability (ability to withstand ramped temperatures in oxic conditions) and carbon isotope signatures. We observed recovery toward our control site bulk Δ 14 C composition at sites further from the wellhead in ~4 years, whereas sites in closer proximity had longer recovery times. The thermographs also indicated temporal changes in the composition of contaminated sediment, with shifts towards higher temperature CO 2 evolution over time at a site near the wellhead, and loss of higher temperature CO 2 peaks at a more distant site.
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