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Is the Oil Gone?
Surface oil at our study sites had all but disappeared by 1992, 3 years after the spill, as the graph below illustrates.
Decline in Surface Oiling
Decline in surface oiling at middle and upper intertidal elevations of the study sites, 1989-1997. The three lines in each plot represent the three different oiling and shoreline treatment classifications we use in the monitoring program.
Two graphs show the percent surface oil cover observed at NOAA study sites each year from 1989 to 1997. The upper graph shows oil cover for control sites, oiled/unwashed sites, and oiled/washed sites at upper intertidal elevations. The lower graph shows oil cover for control sites, oiled/unwashed sites, and oiled/washed sites at middle intertidal elevations. With the exception of an increase in oiling noted in 1990 in the upper intertidal areas, the data show that surface oil at our study sites had all but disappeared by 1992, 3 years after the spill. In the upper intertidal areas, the data for oiled/unwashed sites and oiled/washed sites were close, beginning at over 15% cover in 1989, rising to about 30% in 1991, then diminishing to less than 1% by 1992. In the middle intertidal areas, the percent surface oiling visible at oiled/washed sites was nearly 100% in 1989, dropping to less than 1% by 1992. The surface oiling visible at oiled/unwashed sites was less than 10% in 1989, also dropping to less than 1% by 1992.
However, today there is still residual oil to be found in the impacted areas we study. The remaining oil generally lies below the surface of the beaches in those places that are very sheltered from the actions of wind and wave (which help to break down and remove stranded oil), and those beaches where oil initially penetrated very deeply and was not removed.
Residual Oil
Liquid oil and sheen mobilized at the Bay of Isles, Knight Island, observed by researchers collecting clams in June 1998.
Heavy residual oiling in sediments of Smith Island, June 1998. Oil sheens were observed at this site in undisturbed tide pool water.
Chemical Profiles
Chemical profiles (chromatograms) of alkane compounds in fresh Exxon Valdez oil (top) and residual oil collected in the Bay of Isles in 1996 (bottom). Fewer and lower "spikes" reflect fewer compounds and lower concentration levels.
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Chemical Profiles of Fresh and Residual Oil Profiles (chromatograms) of alkanes in fresh oil from the Exxon Valdez and in residual oil collected in 1996.
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Two graphs show the abundance (x 10,000) of alkane compounds. The top graph shows the chemical profiles (chromatograms) of alkane compounds in fresh Exxon Valdez oil and the bottom graph shows the profiles of residual oil collected in the Bay of Isles in 1996. The top graph shows many high "spikes," indicating more compounds and higher concentration levels in the Exxon Valdez oil. The bottom graph shows few high "spikes," reflecting fewer compounds and lower alkane levels in the residual oil.
Interestingly, despite the fresh appearance of oil at these sites, chemical analysis and biological observations indicate that the oil is actually highly weathered and of such reduced acute toxicity that many intertidal species can tolerate its presence even though it can accumulate in their tissues. Comparing the chemical profiles of fresh Exxon Valdez oil and the oil found at the excavations illustrated below reveals substantially less oil and fewer numbers of oil components remaining.
Other pages in this series
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