A Tale of Two Spills: Novel Science and Policy Implications of an Emerging New Oil Spill Model

Articles A Tale of Two Spills: Novel Science and Policy Implications of an Emerging New Oil Spill Model The 2010 Deepwater Horizon oil release posed the challenges of two types of spill: a familiar spill characterized by buoyant oil, fouling and killing organisms at the sea surface and eventually grounding on and damaging sensitive shoreline habitats, and a novel deepwater spill involving many unknowns. The subsurface retention of oil as finely dispersed droplets and emulsions, wellhead injection of dispersants, and deepwater retention of plumes of natural gas undergoing rapid microbial degradation were unprecedented and demanded the development of a new model for deepwater well blowouts that includes subsurface consequences. Existing governmental programs and policies had not anticipated this new theater of impacts, which thereby challenged decisionmaking on the spill response, on the assessment of natural resource damages, on the preparation for litigation to achieve compensation for public trust losses, and on restoration. Modification of laws and policies designed to protect and restore ocean resources is needed in order to accommodate oil drilling in the deep sea and other frontiers. Keywords: deepwater oil well blowout, natural resource damage assessment, ocean oil drilling policy change, sustaining public trust resources T he Deepwater Horizon (DWH) well blowout in the Gulf of Mexico represents a tale of two spills: the traditional shore-bound surface spill and the novel deep-ocean persistence of intrusions of finely dispersed (atomized) oil, gas, and dispersants. The discharge of oil and gas under high pressure at 1500-meter (m) water depth makes the DWH incident categorically different from all previous wellstudied crude oil releases into the sea. Implementation of legislatively mandated natural resource damage assessment (NRDA) revealed serious gaps in the baseline information on deep-sea communities, their functioning, and their ecotoxicological vulnerability, which demonstrates a need to modify the laws and policies intended to sustain ecosystem services that are at risk from oil and gas drilling. Before the DWH incident, the prevailing scientific model (figure 1a) of maritime oil behavior, fate, and exposure pathways and the consequent impacts on natural resources reflected a synthetic understanding of historical oil spills as occurring typically on the surface or in shallow, nearshore waters (NRC 2003). In traditional spills, crude oil rises rapidly to or remains at the sea surface, and gaseous hydrocarbons escape into the atmosphere with minimal residence time in the water column. Organisms that occupy or frequently encounter the sea surface, such as floating seabirds, can suffer high mortality rates (Piatt 1991). On landfall, this generally cohesive surface oil fouls intertidal and shallow subtidal habitats, which degrades ecosystem services by killing sensitive organisms, including key providers of structural habitat, such as salt-marsh macrophytes and mangroves (e.g., Jackson et al. 1989). Oil can persist when it is buried in anoxic, nutrient-limited sediments, where weathering is inhibited (Boufadel et al. 2010), leading to chronic biological exposures that can reduce production (Culbertson et al. 2008, Michel et al. 2009) or reproductive output and indirectly suppress the population recovery of exposed animals for decades (Teal and Howarth 1984, Bodkin et al. 2002, Culbertson et al. 2007, Esler and Iverson 2010) by depressing their fitness (Peterson 2001, Rice et al. 2001). In stark contrast, the DWH blowout occurred in deep (1500 m) offshore waters, where a highly turbulent discharge of hot, pressurized oil and gas entrained cold seawater under BioScience 62: 461–469. ISSN 0006-3568, electronic ISSN 1525-3244. © 2012 by American Institute of Biological Sciences. All rights reserved. Request permission to photocopy or reproduce article content at the University of California Press’s Rights and Permissions Web site at www.ucpressjournals.com/ reprintinfo.asp. doi:10.1525/bio.2012.62.5.7 www.biosciencemag.org May 2012 / Vol. 62 No. 5 • BioScience 461 Charles H. Peterson, Sean S. Anderson, Gary N. Cherr, Richard F. Ambrose, Shelly Anghera, Steven Bay, Michael Blum, Robert Condon, Thomas A. Dean, Monty Graham, Michael Guzy, Stephanie Hampton, Samantha Joye, John Lambrinos, Bruce Mate, Douglas Meffert, Sean P. Powers, Ponisseril Somasundaran, Robert B. Spies, Caz M. Taylor, Ronald Tjeerdema, and E. Eric Adams Articles high pressures and produced a variety of dispersed phases, including small oil droplets, gas bubbles, oil–gas emulsions, and gas hydrates. An injection of 0.77 million gallons of chemical dispersants at the wellhead, beginning 24 days after the well blowout, also contributed to the dispersion of the oil (Federal Interagency Solutions Group 2010). The collective buoyancy of the oil and gas created a rising plume, but unlike a continuous-phase (e.g., sewage) plume, much of the oil and gas separated from the entrained seawater as it apparently became trapped by depth-related physical discontinuities and was deflected laterally by ambient currents (Socolofsky et al. 2011). The dissolution into seawater of water-soluble petroleum compounds, including most of the methane, ethane, and propane and large fractions of water-soluble aromatic compounds, explains the elevated levels of petroleum hydrocarbons retained in the subsurface plume at a water depth of 1100 m (Reddy et al. 2012). A plume of hydrocarbon-enriched waters was observed by others at depths of 800–1200 m (Camilli et al. 2010, Valentine et al. 2010, Joye et al. 2011), at which hydrocarbons 462 BioScience • May 2012 / Vol. 62 No. 5 www.biosciencemag.org Figure 1. Contrast of (a) the traditional model for crude oil fate and effects that prevailed before the Deepwater Horizon (DWH) blowout, based on synthesis of experience with nearshore maritime spills in shallow water, and (b) the newly emerging and still-developing model of a deepwater blowout like the DWH spill. Abbreviation: m, meters. stimulated intense heterotrophic microbial activity (Kessler et al. 2011) and may have entered deep-sea food chains through pelagic primary consumers (as was exhibited by nearshore incorporation in mesozooplankton of petroleum carbon from DWH oil; Graham WM et al. 2010). The occurrence of a deepwater spill of this magnitude and with these characteristics is unprecedented and clearly warrants a new conceptual oil spill model (figure 1b). Although about half of the 4.9 million barrels of DWH oil did rise to the sea surface (Federal Interagency Solutions Group 2010), it became weathered during ascent, such that the oil reaching the surface appeared reddish-brown in color and was less cohesive than crude oil discharged onto the surface would be (figure 1a, 1b). Liquid oil droplets enriched with denser compounds, such as asphaltenes, descended toward the seafloor (Reddy et al. 2012). In (...truncated)