March 24, 2009

• Ecological Recovery of Prince William Sound Following the Exxon Valdez Oil Spill

  Depending on who one asks, the biota of Prince William Sound continue to display severe or catastrophic effects twenty years after the oil spill, or the ecology is completely recovered, or the facts are something between those extremes.

  Natives, who for generations depended on the sea harvest and what they could forage along the coastline, say that it has become difficult or impossible to subsist there in the old ways.  Commercial fishers point to the total collapse of the herring fishery, and bureaucrats say that there is no proof that it would not have collapsed anyway, even if the spill and cleanup had never occurred.

  Many researchers agree that along the coastline the cleanup had a destructive impact, but there is no consensus on what proportion of the lasting damage is from the spill, as opposed to from the cleanup.

  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.

  [from a study commissioned by Exxon]

  From 1995 through 1997, the Alaska Department of Fish and Wildlife studied harlequin ducks.  Since there was no baseline data for these ducks in the region, they compared populations in the unoiled eastern part of Prince William Sound with those in the west where the oil came ashore.

  Based on our results and the recovery criteria (Exxon Valdez Oil Spill Trustee Council 1996), harlequin ducks have not recovered from the effects of the Exxon Valdez oil spill.  A similar population structure in EPWS (unoiled) and WPWS (oiled) indicates that the population in oiled areas of WPWS has the potential to recover from the effects of the EVOS.  However, our trend analysis indicates that the population in oiled areas is still declining.

  wildlife.alaska.gov

  From the National Oceanic and Atmospheric Administration’s Office of Response and Restoration:

  Remaining Impacts

  

  Although Prince William Sound has proved to be surprisingly resilient, impacts from the spill remain:

      * Deeply penetrated oil continues to visibly leach from a few beaches, as on Smith Island .
      * In some areas, intertidal animals such as mussels are still contaminated by oil.
      * Some rocky sites that were stripped of heavy plant cover by high-pressure, hot-water cleaning remain mostly bare rock.
      * Rich clam beds that suffered high mortalities from oil and extensive beach cleaning have not repopulated to their previous levels.

  While these are mostly isolated examples, they provide a basis for gauging the overall recovery of oiled areas. Prince William Sound has made a remarkable recovery from a severe injury, but it remains an ecosystem in transition.

  report: Assessing Environmental Harm

  The Encyclopedia of Earth has the most comprehensive and authoritative coverage of the spill, cleanup, and recovery of any I have found.  I am happy that my search for data for this post turned up EOEarth.  I have a lot to learn there.

  A 2001 National Oceanic and Atmospheric Administration (NOAA) study surveyed 96 sites along 8,000 miles of coastline.

    The survey distinguished between surface and buried oil. Buried or subsurface oil is of greater concern than surface oil. Subsurface oil can remain dormant for many years before being dispersed and is more liquid, still toxic, and may become biologically available. A disturbance event such as burrowing animals or a severe storm reworks the beach and can reintroduce unweathered oil into the water. Results of the summer shoreline survey showed that the oil remaining on the surface of beaches in Prince William Sound is weathered and mostly hardened into an asphalt-like layer. The toxic components of this type of surface oil are not as readily available to biota, although some softer forms do cause sheens in tide pools.

  The survey indicates a total area of approximately 20 acres of shoreline in Prince William Sound are still contaminated with oil. Oil was found at 58 percent of the 91 sites assessed and is estimated to have the linear equivalent of 5.8 km of contaminated shoreline.

  

  In addition to the estimated area of remaining oiled beach, several other important points were evident:

     1. Surface oil was determined to be not a good indicator of subsurface oil.
     2. Twenty subsurface pits were classified as heavily oiled. Oil saturated all of the interstitial spaces and was extremely repugnant. These “worst case” pits exhibited an oil mixture that resembled oil encountered in 1989 a few weeks after the spill—highly odiferous, lightly weathered, and very fluid.
     3. Subsurface oil was also found at a lower tide height than expected (between 0 and 6 feet), in contrast to the surface oil, which was found mostly at the highest levels of the beach. This is significant, because the pits with the most oil were found low in the intertidal zone, closest to the zone of biological production, and indicate that the survey estimates are conservative at best.

  If you ask a fisherman from Kodiak Island, a villager from the town of Valdez, an Exxon engineer, or a NOAA biologist, you are likely to receive such different answers that you may wonder if they heard the same question. In particular, disagreements exist between Exxon and government-funded scientists, and unknowns persist, especially in understanding how multiple processes combine to drive observed dynamics.

  Despite this, there are some things known with a high degree of certainty: oil persisted beyond a decade in surprising amounts and in toxic forms, was sufficiently bioavailable to induce chronic biological exposures, and had long-term impacts at the population level. Three major pathways of long-term impacts emerge: (1) chronic persistence of oil, biological exposures, and population impacts to species closely associated with shallow sediments; (2) delayed population impacts of sublethal doses compromising health, growth, and reproduction; and (3) indirect effects of trophic and interaction cascades, all of which transmit impacts well beyond the acute-phase mortality.

  eoearth.org/article/Exxon_Valdez_oil_spill

  

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