Exxon Valdez oil continues to pollute, 13 years later
Researchers from the US National Oceanic and Atmospheric Administration (NOAA) told a conference last week that oil from the 1989 Exxon Valdez spill is continuing to damage Prince William Sound.
The Auke Bay Laboratory has been conducting ongoing research on the effects of the spill on fish and invertebrates of Prince William Sound and monitoring the persistence of the oil in the environment, and has funding to continue monitoring until 2005.
Its results so far show that oil remains in the affected area and that “intertidal and shallow subtidal habitats are still contaminated; some species have not recovered; and the production of the ecosystem appears ‘out of sync’ as major salmon and herring fisheries have not returned to stability.”
In the survey, the Auke Bay Laboratory sampled 96 beaches in western Prince William Sound to determine the amount of oil remaining in the upper inter-tidal areas. Its aim was to check recovery trends and find out if the remaining oil still had the characteristic composition of that spilled from the Exxon Valdez.
The sample sites were selected at random from over 700 sites that had been classified as heavily or moderately oiled by previous shoreline surveys, with ten additional beaches chosen from sites suggested by residents of the area. In all, around 10,000 sample pits were hand-dug in the upper inter-tidal zones, with sediments taken to check for the amount and quality of oil.
“A casual observer would not likely see signs of the oil spill today in Prince William Sound,” comments the NOAA. “However, Exxon Valdez oil persists in certain environments, especially in areas sheltered from weathering processes, such as in the subsurface under selected gravel shorelines, and in some soft substrates containing peat.”
It notes that in terms of recovery: “A commonly used definition, the ‘return to conditions as they were before the spill’ is neither practical nor ecologically realistic for changeable intertidal systems.”
NOAA’s scientists have used parallelism, a statistical test that measures whether the amount of plants and animals at oiled sites changes over time in a similar way to those at unoiled sites, to estimate recovery.
They found ongoing differences between oiled and unoiled sites, suggesting incomplete recovery, include lower populations of local creatures at oiled sites and different grain size structures in oiled beaches, though NOAA notes that some of the differences could be natural.
Oil remained on at least 53 of the beaches in various states, from fresh mousse to weathered tar balls. Preliminary NOAA estimates suggest that some 10,000 gallons of the original 11 million from the spill remain spread across 4.3 miles of shoreline, with the total reducing by around 26% per year. The oil is also most prevalent in sensitive areas below the beach surface and the lower intertidal zones where clams and other molluscs live.
“We think the oil will be detectable in some places for at least another decade, and may persist for perhaps several decades,” said Jeffrey W. Short, a research scientist at Auke Bay. “But even now, the lingering effects of this spill are confined to a relatively small area that was the most heavily impacted part of the sound initially, and are not affecting injured species at the population level.”
The clean-up also appears to have adversely affected oiled sites. “Current evidence implies that oiled and hot-water washed sites initially suffered more severe declines in population abundance than oiled and not-washed sites,” NOAA says.
The conference also heard from US Geological Survey researchers whose studies showed that sea otters and harlequin ducks in Prince William Sound also show continuing evidence of pollution, carrying high levels of enzymes associated with exposure to hydrocarbons.
The Exxon Valdez Office of Oil Spill (EVOS) Damage Assessment and Restoration manages research and monitoring projects for the Exxon Valdez Trustee Council, which administers the US$900 million that Exxon paid to settle the various charges against it. Several agencies are involved in these research and monitoring efforts, including the Auke Bay Laboratory, National Marine Fisheries Service (NMFS) and a number of contractors.