Oil Remains - 0 views
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largest and most productive estuaries in North America.
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However, in 1993 the EVOS Trustee Council funded an additional survey that estimated 7 km of shoreline were still contaminated with subsurface oil.
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Because a significant survey of Prince William Sound had not been conducted since 1993 and the cumulative extent of the remaining oil was unknown, concerns were generated by the public and scientific communities about the oil’s possible continuing effects on humans and fauna potentially exposed to the oil directly or indirectly.
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Without an accurate assessment of the extent of the remaining oil, subsistence food-gatherers, consumers of commercial fish products from the area, and tourists have used mostly anecdotal evidence as the basis for economic decisions regarding resource utilization in the affected area.
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Consequently, the Auke Bay Laboratory (ABL) with funding from the EVOS Trustee Council, took on the task of assessing the remaining oil along the shorelines of Prince William Sound during the summer of 2001
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The primary objective of the project was to measure the amount of oil remaining in the intertidal zone of Prince William Sound. Secondary objectives include determining the rate of decline of oil on these beaches, estimating the persistence of the remaining oil, and correlating the remaining oil with geomorphological features.
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heavily and moderately oiled
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The 2001 survey adopted a stratified random/adaptive sampling (SRAS) design. Two random pits were excavated to a depth of 0.5 m (1.6 feet) in every stratified block (0.5-m verticle drop in tide height) within a grid system established at each site. If subsurface oil was discovered in any of the randomly stratified origin pits, then additional adaptive pits were excavated above, below, to the right, and to the left of the origin pit until the extent of the oil patch was determined.
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Buried or subsurface oil is of greater concern than surface oil.
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Subsurface oil can remain dormant for many years before being dispersed and is more liquid, still toxic, and may become biologically available.
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A disturbance event such as burrowing animals or a severe storm reworks the beach and can reintroduce unweathered oil into the water.
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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.
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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 (Table 3). 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 our estimates are conservative at best.
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The possibility of continuing low level chronic effects of the Exxon Valdez oil spill seem very real now, although measurable population effects would be very difficult to detect in wild populations.
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Sea otters and harlequin ducks fall into this category
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such as sea otters, harlequin ducks, and their intertidal prey.
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The last beach assessment was completed in September 2001. Supporting chemical analyses will be completed in fall 2002, and a final report with statistical analyses and conclusions will be completed by April 2002.
