Exxon Valdez Oil Spill Shoreline Treatment Effects Study

NOAA

Prince William Sound, Alaska

Prince WilliamSound

Hart Crowser conducted field sampling, analyzed the data, and reported on the biological recovery of the Prince William Sound shorelines from the effects of the 1989 Exxon Valdez oil spill and subsequent shoreline treatments. This process was a long-term program conducted for Exxon in 1989 and jointly by NOAA and Hart Crowser from 1990 through 1997. Two areas of great uncertainty and misunderstanding about the effects of oil and cleanup treatments on shorelines were investigated:

  • The length of time required for damaged ecosystems to recover and the effects of treatment activities on marine life
  • The extent to which treatment enhances or delays recovery

During this study period, we sampled biota at sheltered rocky and mixed-soft sites subjected to three degrees of disturbance:

  • Unoiled
  • Oiled but not hot water washed
  • Oiled and hot water washed

The majority of the community dominants, including rockweed, mussels, barnacles, limpets, drills, and littorines, survived 1989 on oiled rocky shores that were not high-pressure hot water washed. These areas appeared to be nearly completely recovered by 1991, although subsequent monitoring has revealed oscillations in species abundances that exceed those on unoiled beaches.

Hot water treatments used to remove crude oil from the beaches in 1989 had severe short-term impacts on intertidal epibenthos. Some high-pressure hot water treated rocky shores that were stripped of biota in 1989 showed very slow colonization through 1995; other areas that appeared to be nearly recovered in 1992 suffered severe declines in dominant taxa in 1995. The dominant age class of rockweed, which began life following hot-water treatment, matured and died off resulting in declines of associated fauna. Effects of hydraulic flushing of oil from mixed gravel/sand/silt beaches in 1989 remained evident in the infauna through 1994. Hardshelled clam populations and other taxa (bivalves, polychaetes, gastropods) decimated by the beach washing were very slow to recolonize despite the absence of oil in the sediments since 1990. Unwashed areas with high residual oil content have experienced excellent recolonization by these organisms. Factors influencing these recovery patterns through 1996 results were explored.
In 2010, we participated in field surveys of clam and infauna assemblages on oiled beaches that were washed or not washed following the Exxon Valdez oil spill. This study included sites sampled in the years following the oil spill and examined the relationship between geomorphologic changes resulting from the cleanup and clam populations 20 years later.