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To request reprints or more information from these projects, please send email to: info@ecologicalrisk.com.
Prince William Sound - Exxon Valdez
A project presently underway by Harwell Gentile and Associates, LC, for the ExxonMobil Corporation is addressing the issue of the ecological significance of any residual effects from the Exxon Valdez oil spill (EVOS) on Prince William Sound (PWS), Alaska.
The Exxon Valdez oil spill occurred on 24 March 1989, with more than 250,000 barrels of Alaska North Slope crude oil released into northeastern Prince William Sound. Within two days winds in excess of 70 mph drove much of the surfaced oil to the southwest, forming mousse, a water-in-oil emulsion that affected the fate-and-transport and exposures of the spilled oil. About half of the spilled oil landed on the shoreline or the intertidal zone of the Alaskan coast, so that almost 500 miles of Prince William Sound (about 16% of the shoreline) and over 800 miles of the Gulf of Alaska (about 14% of the shoreline) were oiled to some degree. Because Prince William Sound is such a highly dynamic system, with extreme winter storms and wave/tidal action, most of the beached oil dispersed back into the ocean within three years after the spill, and only 2% of the volume of oil spilled remained on Prince William Sound beaches by the end of 1992.
Biological effects from the spill resulted from both toxicological responses from the chemicals in the oil (particularly PAHs) and physical oiling which caused smothering and hyperthermia. Especially visible was the significant loss of seabirds from oiling, with estimates of over 375,000 seabirds being killed. However, although the PAHs were readily detectable in the water, their concentrations were well below acute toxicity levels for marine animals, even right after the spill. In addition to the stressors from the crude oil itself, a massive clean-up operation was undertaken after the spill throughout the summers of 1989-91, and more than 11,000 people and 1100 boats cleaned over 1000 miles of shorelines and intertidal areas of the Sound and Gulf using high-pressure and/or high-temperature water removal, surfactants, and manual physical removal of oil. There was clear evidence that in many cases the clean-up efforts constituted a more significant stressor to shoreline and intertidal biota than the physical and toxicological stressors from the spill. For example, some of the intertidal cleaning essentially removed all of the macroalgal community from rocky surfaces, extending the time to recovery of those areas by about two years.
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As a part of a US EPA Risk Forum project, Drs. Gentile and Harwell developed a framework for assessing ecological significance (Gentile and Harwell 1998), including criteria for the nature, intensity, spatial extent, duration, and other factors concerning a stressor, as well as criteria for distinguishing an ecological effect from the noise of natural variability. For example, if an anadromous fish population in Prince William Sound varies from one year to the next by more than an order-of-magnitude, a change of say 10% is simply not ecologically significant. Another key issue is attributable risk, i.e., assessing if any ecologically significant effects are caused by EVOS rather than some other natural or anthropogenic stressor. For example, there exist small, mostly isolated pockets of residual EVO, potentially presenting an exposure risk of PAHs to Prince William Sound biota; however, there are many other sources of PAHs in PWS, such as releases from commercial shipping, abandoned human activity sites, and natural oil seeps in the Gulf of Alaska. As a result, relating an exposure risk of PAHs in Prince William Sound to the EVOS event vs. the other sources of PAHs requires a multiple-lines-of-evidence approach.
Prince William Sound is affected by many natural stressors, such as natural climate and oceanographic variability that is largely responsible for the large differences in fish populations, and continuing effects from the massive 1964 Alaskan earthquake, which caused uplifting of more than 10 m in some areas of the Sound. In addition, there are many human stressors on PWS, such as over-fishing, harvesting sea otters almost to extinction for their fur, and global climate change. We use the attributable risk approach to assess current risks to PWS from EVOS.
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Our assessments provided an overall synthesis view of the current health of Prince William Sound to assess if any impacts today are ecologically significant and attributable to Exxon Valdez oil spill. We applied the criteria that we developed for determining ecological significance to about two dozen valued ecosystem components (VECs) of PWS, including primary producers, filter feeders, fish and bird primary consumers, fish and bird top predators, a bird scavenger, mammalian primary consumers and top predators, biotic communities, ecosystem-level properties of trophodynamics and biogeochemical processes, and landscape-level properties of habitat mosaic and wilderness quality. We concluded that none of these has any ecologically significant effects that are detectable at present, with the exception of one pod of orcas and possibly one subpopulation of sea otters; however, in both those cases, PWS-wide populations appear to have fully recovered.
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See Harwell and Gentile (2006) for the full analysis (abstract reproduced here). See also the summary for a presentation given at the SETAC Annual Meeting, November 2005 (presentation - 3M pdf file).
References Cited:
Gentile, John H. and Mark A. Harwell. 1998. The issue of significance in ecological risk assessments. Human and Ecological Risk Assessment 4(4): 815-828.
Harwell, Mark A. and John H. Gentile. 2006. Ecological significance of residual exposures and effects from the Exxon Valdez oil spill. Integrated Environmental Assessment & Management 2(3): 204-246.
The US Army Corps of Engineers, New York District conducted a comprehensive feasibility study for a project on shore protection and storm damage reduction for the southern shore of Long Island, New York, from Fire Island Inlet to Montauk Point (known as the FIMP project).
HGA facilitated a workshop in 2000 to construct conceptual models of the interactions between significant components of coastal ecosystems in the coastal region of Long Island, New York from Fire Island to Montauk Point.
The goal in developing the conceptual models was to describe the functional relationships among the natural biotic, abiotic (physical, geological, and chemical), and anthropogenic components of the South Shore ecosystem in sufficient detail to assess the ecological implications of management decisions. The geographic extent of the study area was the immediate watershed on the south shore of Long Island from Fire Island to Montauk Point, including Great South Bay, Moriches Bay, Shinnecock Bay, the larger barrier island ecosystem, and the adjacent coastal waters to a depth of 30 meters.
The initial set of these ecological conceptual models was developed at a workshop held on Long Island in June 2000, facilitated by the scientists associated with Harwell Gentile & Associates, LC (HGA).
For a more detailed overview, click here (pdf)
References:
US Army Engineer Research and Development Center and Harwell Gentile & Associates, LC. 2000. Conceptual Models for Coastal Long Island Ecosystems: Fire Island to Montauk Point Reformulation Study. Letter report, US Army Engineer Research and Development Center, Vicksburg, MS. July 2000. download report here (4.2M pdf file)
Florida Department of Environmental Protection
The Florida Department of Environmental Protection is responsible for managing the conduct assessments of the risks from the many hazardous waste sites in Florida. Parties provide assessments conducted by their contractors to FDEP for review and the basis of remedial decisions. FDEP consults with HGA to provide an independent evaluation of the ecological risk assessments that are submitted. This partnership has resulted in the review and decisions for over 15 sites to date. Part of the interpretation of the risk assessments for these sites involves putting the risks into context that is, applying criteria to determine if the risks are significant. The criteria and processed used for this assessment follow those in U.S. EPA’s report on Ecological Significance.
Mining operations over the last century have left over 10,000 square miles of heavy metal contamination in the Coeur d’Alene basin. In order to characterize the magnitude and extent of contamination and risk, a risk-based framework was used to divide the area into sub-units and to identify remedial source and ecological goals. Conceptual models were developed for each sub-unit and for rivers within those units to identify the primary sources of contamination and to allocate resources. This study involved EPA, NOAA, the Coeur d’Alene Tribal Nation, and the Department of Justice. HGAs role in this study was to conduct a series (10) of workshops that resulted in setting goals for each sub-unit and developing conceptual models to support remediation efforts.
ORIMULSION™ Comparative Risk Assessment
Florida Power and Light contracted with the University of Miami, including the expertise of Drs. Harwell and Gentile, to conduct a comparative ecological risk assessment at its Manatee power plant in Tampa bay. This study focused on the comparative risks from hypothetical spills of Fuel Oil #6 and a new fuel Orimulsion at multiple locations within the Tampa Bay ecosystem. The study employed an integrated suite of models – hydrodynamic, sea-grasses, mangroves, and fisheries – to create a wide range of possible spill scenarios. Over 100 plausible scenarios were examined and compared to determine the comparative risks of these two fuel types. The conclusion was that Fuel Oil # 6 posed a far more serious threat and risks to the shallow inter-tidal and shoreline habitats that did Orimulsion. The information developed in this study was used to support a permit application for conversion of the Manatee plant to the alternative fuel.
For a more detailed overview, click here (pdf)
Project information coming soon.
Project information coming soon.
Project information coming soon.
© HGA, LC 2006-2007
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