Helen K. White

Impact of the Deepwater Horizon oil spill on a deep-water coral community in the Gulf of Mexico

To assess the potential impact of the Deepwater Horizon oil spill on offshore ecosystems, 11 sites hosting deep-water coral communities were examined 3 to 4 mo after the well was capped. Healthy coral communities were observed at all sites >20 km from the Macondo well, including seven sites previously visited in September 2009, where the corals and communities appeared unchanged. However, at one site 11 km southwest of the Macondo well, coral colonies presented widespread signs of stress, including varying degrees of tissue loss, sclerite enlargement, excess mucous production, bleached commensal ophiuroids, and covering by brown flocculent material (floc). On the basis of these criteria the level of impact to individual colonies was ranked from 0 (least impact) to 4 (greatest impact). Of the 43 corals imaged at that site, 46% exhibited evidence of impact on more than half of the colony, whereas nearly a quarter of all of the corals showed impact to >90% of the colony. Additionally, 53% of these corals’ ophiuroid associates displayed abnormal color and/or attachment posture. Analysis of hopanoid petroleum biomarkers isolated from the floc provides strong evidence that this material contained oil from the Macondo well. The presence of recently damaged and deceased corals beneath the path of a previously documented plume emanating from the Macondo well provides compelling evidence that the oil impacted deep-water ecosystems. Our findings underscore the unprecedented nature of the spill in terms of its magnitude, release at depth, and impact to deep-water ecosystems.

Sustainable energy from deep ocean cold seeps

Two designs of benthic microbial fuel cell (BMFC) were deployed at cold seeps in Monterey Canyon, CA, unattended for between 68 and 162 days. One design had a cylindrical solid graphite anode buried vertically in sediment, and the other had a carbon fiber brush anode semi-enclosed in a chamber above the sediment–water interface. Each chamber included two check valves to allow fluid flow from the sediment into the chamber. On average, power outputs were 0.2 mW (32 mW m−2 normalized to cross sectional area) from the solid anode BMFC and from 11 to 56 mW (27–140 mW m−2) during three deployments of the chambered design. The range in power produced with the chambered BMFC was due to different valve styles, which appear to have permitted different rates of chemical seepage from the sediments into the anode chamber. Valves with the lowest breaking pressure led to the highest power production and presumably the highest inputs of electron donors. The increase in power coincided with a significant change in the microbial community associated with the anode from being dominated by epsilonproteobacteria to a more diverse community with representatives from deltaproteobacteria, epsilonproteobacteria, firmicutes, and flavobacterium/cytophaga/bacterioides (FCB). The highest levels of power delivered by the chambered BMFC would meet the energy requirements of many oceanographic sensors marketed today. In addition, these BMFCs did not exhibit signs of electrochemical passivation or progressive substrate depletion as is often observed with buried anodes.

Substrate Degradation Kinetics, Microbial Diversity, and Current Efficiency of Microbial Fuel Cells Supplied with Marine Plankton

ABSTRACT The decomposition of marine plankton in two-chamber, seawater-filled microbial fuel cells (MFCs) has been investigated and related to resulting chemical changes, electrode potentials, current efficiencies, and microbial diversity. Six experiments were run at various discharge potentials, and a seventh served as an open-circuit control. The plankton consisted of a mixture of freshly captured phytoplankton and zooplankton (0.21 to 1 mm) added at an initial batch concentration of 27.5 mmol liter−1 particulate organic carbon (OC). After 56.7 days, between 19.6 and 22.2% of the initial OC remained, sulfate reduction coupled to OC oxidation accounted for the majority of the OC that was degraded, and current efficiencies (of the active MFCs) were between 11.3 and 15.5%. In the open-circuit control cell, anaerobic plankton decomposition (as quantified by the decrease in total OC) could be modeled by three terms: two first-order reaction rate expressions (0.79 day−1 and 0.037 day−1, at 15°C) and one constant, no-reaction term (representing 10.6% of the initial OC). However, in each active MFC, decomposition rates increased during the third week, lagging just behind periods of peak electricity generation. We interpret these decomposition rate changes to have been due primarily to the metabolic activity of sulfur-reducing microorganisms at the anode, a finding consistent with the electrochemical oxidization of sulfide to elemental sulfur and the elimination of inhibitory effects of dissolved sulfide. Representative phylotypes, found to be associated with anodes, were allied with Delta-, Epsilon-, and Gammaproteobacteria as well as the Flavobacterium-Cytophaga-Bacteroides and Fusobacteria. Based upon these results, we posit that higher current efficiencies can be achieved by optimizing plankton-fed MFCs for direct electron transfer from organic matter to electrodes, including microbial precolonization of high-surface-area electrodes and pulsed flowthrough additions of biomass.

Quantitative population dynamics of microbial communities in plankton-fed microbial fuel cells

This study examines changes in diversity and abundance of bacteria recovered from the anodes of microbial fuel cells (MFCs) in relation to anode potential, power production and geochemistry. MFCs were batch-fed with plankton, and two systems were maintained at different potentials whereas one was at open circuit for 56.8 days. Bacterial phylogenetic diversity during peak power was assessed from 16S rDNA clone libraries. Throughout the experiment, microbial community structure was examined using terminal restriction fragment length polymorphism. Changes in cell density of key phylotypes, including representatives of δ-, ɛ-, γ-proteobacteria and Flavobacterium-Cytophaga-Bacteroides, were enumerated by quantitative PCR. Marked differences in phylogenetic diversity were observed during peak power versus the final time point, and changes in microbial community structure were strongly correlated to dissolved organic carbon and ammonium concentrations within the anode chambers. Community structure was notably different between the MFCs at different anode potentials during the onset of peak power. At the final time point, however, the anode-hosted communities in all MFCs were similar. These data demonstrate that differences in growth, succession and population dynamics of key phylotypes were due to anode potential, which may relate to their ability to exploit the anode as an electron acceptor. The geochemical milieu, however, governs overall community diversity and structure. These differences reflect the physiological capacity of specific phylotypes to catabolize plankton-derived organic matter and exploit the anode of an MFC for their metabolism directly or indirectly through syntrophy.

Degradation of oil by fungi isolated from Gulf of Mexico beaches

Fungi of the Ascomycota phylum were isolated from oil-soaked sand patties collected from beaches following the Deepwater Horizon oil spill. To examine their ability to degrade oil, fungal isolates were grown on oiled quartz at 20°C, 30°C and 40°C. Consistent trends in oil degradation were not related to fungal species or temperature and all isolates degraded variable quantities of oil (32-65%). Fungal isolates preferentially degraded short (<C18; 90-99%) as opposed to long (C19-C36; 7-87%) chain n-alkanes and straight chain C17- and C18-n-alkanes (91-99%) compared to their branched counterparts, pristane and phytane (70-98%). Polycyclic aromatic hydrocarbon (PAH) compounds were also degraded by the fungal isolates (42-84% total degraded), with a preference for low molecular weight over high molecular weight PAHs. Overall, these findings contribute to our understanding of the capacity of fungi to degrade oil in the coastal marine environment.

Unresolved Complex Mixture (UCM) in Coastal Environments Is Derived from Fossil Sources

The unresolved complex mixture (UCM) frequently dominates organic extracts isolated from estuarine and coastal sediments in the vicinity of industrial centers. Despite an obvious link to a petroleum source, speculation exists that biogenic sources also contribute to the UCM. To determine the source of the UCM to these environments, natural abundance radiocarbon (Δ(14)C) and stable carbon (δ(13)C) isotopic composition of the UCM solvent-extracted from coastal sediments, road dust, and urban atmospheric particulate in the United States was measured. Extracts of UCM and separate saturate and aromatic fractions from all samples are predominantly (>90%) fossil-derived and hence have a petroleum source. Even the polar fraction of the UCM, which has a Δ(14)C composition reflecting contributions from recently photosynthesized carbon (-665‰), is composed of ~66% fossil carbon indicating the presence of petroleum residues that have been transformed into more polar derivatives. The δ(13)C of the UCM had consistent values (-27.65 ± 0.51‰; n = 16) for all but one sample, indicating a common origin of the UCM. We conclude that in coastal areas dominated by human activities whole fractions of the UCM, as well as separate saturate, aromatic, and polar fractions, are principally derived from petroleum sources.

Reply to Boehm and Carragher: Multiple lines of evidence link deep-water coral damage to Deepwater Horizon oil spill

Our original study (1) used visual inspection as well as biological and geochemical analyses of corals and the surrounding sediment to provide complementary and compelling evidence linking the Deepwater Horizon (DWH) oil spill to the presence of damaged deep-water corals and brittle stars 11 km from the site of the leaking oil.

Long-term weathering and continued oxidation of oil residues from the Deepwater Horizon spill

To investigate the long-term weathering of oil from the Deepwater Horizon (DWH) incident, oil-soaked sand patties were collected from Gulf of Mexico beaches from Florida to Alabama over a three-year period from 2012 to 2014. Analysis of oil residues by gas chromatography with flame ionization detection (GC-FID), thin-layer chromatography with flame ionization detection (TLC-FID), and Fourier transform infrared spectroscopy (FT-IR) indicated uniformity in their chemical composition. Some variability within and between samples was observed, arising from differences in exposure to light and water, which increase the amount of weathering. Oxygenated hydrocarbons (OxHC) produced by weathering processes dominate the majority of oil residues. These OxHC have continued recalcitrance in the environment, and increase in relative abundance over time. Analyses of the bulk characteristics of oil residues via TLC-FID and FT-IR should be continued as these techniques provide important insight into the weathering state of oil residues.

Deep-sea coral δ13C: A tool to reconstruct the difference between seawater pH and δ11B-derived calcifying fluid pH

The boron isotopic composition (?11B) of coral skeleton is a proxy for seawater pH. However, ?11B-based pH estimates must account for the pH difference between seawater and the coral calcifying fluid, ?pH. We report that skeletal ?11B and ?pH are related to the skeletal carbon isotopic composition (?13C) in four genera of deep-sea corals collected across a natural pH range of 7.89–8.09, with ?pH related to ?13C by ?pH?=?0.029?×??13C?+?0.929, r2?=?0.717. Seawater pH can be reconstructed by determining ?pH from ?13C and subtracting it from the ?11B-derived calcifying fluid pH. The uncertainty for reconstructions is ±0.12 pH units (2 standard deviations) if estimated from regression prediction intervals or between ±0.04 and ±0.06 pH units if estimated from confidence intervals. Our new approach quantifies and corrects for vital effects, offering improved accuracy relative to an existing ?11B versus seawater pH calibration with deep-sea scleractinian corals.

Partial Photochemical Oxidation Was a Dominant Fate of Deepwater Horizon Surface Oil

Following the Deepwater Horizon (DWH) blowout in 2010, oil floated on the Gulf of Mexico for over 100 days. In the aftermath of the blowout, substantial accumulation of partially oxidized surface oil was reported, but the pathways that formed these oxidized residues are poorly constrained. Here we provide five quantitative lines of evidence demonstrating that oxidation by sunlight largely accounts for the partially oxidized surface oil. First, residence time on the sunlit sea surface, where photochemical reactions occur, was the strongest predictor of partial oxidation. Second, two-thirds of the partial oxidation from 2010 to 2016 occurred in less than 10 days on the sunlit sea surface, prior to coastal deposition. Third, multiple diagnostic biodegradation indices, including octadecane to phytane, suggest that partial oxidation of oil on the sunlit sea surface was largely driven by an abiotic process. Fourth, in the laboratory, the dominant photochemical oxidation pathway of DWH oil was partial oxidation to oxygenated residues rather than complete oxidation to CO2. Fifth, estimates of partial photo-oxidation calculated with photochemical rate modeling overlap with observed oxidation. We suggest that photo-oxidation of surface oil has fundamental implications for the response approach, damage assessment, and ecosystem restoration in the aftermath of an oil spill, and that oil fate models for the DWH spill should be modified to accurately reflect the role of sunlight.