Vertical Distribution and Probability of Encountering Intertidal Exxon Valdez Oil on Shorelines of Three Embayments within Prince William Sound, Alaska

Abstract

We examined 32 shorelines selected at random in 2003 from shorelines in Herring Bay, Lower Pass, and Bay of Isles in Prince William Sound, Alaska, to examine the vertical distribution of oil remaining from the 1989 Exxon Valdez oil spill and to estimate the probability that sea otters and ducks would encounter oil while foraging there. On each shoreline, sampling was stratified by 1-m tide height intervals and randomly located 0.25 m2 sampling quadrats were examined for evidence of surface and subsurface oil. Oil from the T/V Exxon Valdezwasfound on 14 shorelines, mainly in Herring Bay and Lower Pass, with an estimated 0.43 ha covered by surface oil and 1.52 ha containing subsurface oil. Surface and subsurface oil were most prevalent near the middle of the intertidal and had nearly symmetrical distributions with respect to tide height. Hence, about half the oil is in the biologically rich lower intertidal, where predators may encounter it while disturbing sediments in search of prey. The overall probability of encountering surface or subsurface oil is estimated as 0.0048, which is only slightly greaterthan our estimated probability of encountering subsurface oil in the lower intertidal of Herring Bay or Lower Pass. These encounter probabilities are sufficient to ensure that sea otters and ducks that routinely excavate sediments while foraging within the intertidal would likely encounter subsurface oil repeatedly during the course of a year.

Slightly Weathered Exxon Valdez Oil Persists in Gulf of Alaska Beach Sediments after 16 Years

“…Within PWS during the early stages of the spill, less viscous oil readily percolated into the generally finer-grained beaches (10). As the spill progressed along the GOA, the often greater porosity of more exposed beaches allowed the increasingly viscous oil to percolate into them as well (11,12).…”

“…The percent of oiled quadrats classified as HOR, MOR, LOR was 6, 41, and 53% in 2001, compared with 7, 20, and 73% in 2005, a change that was not statistically significant ( 2 ) 2.09, P ) 0.35, df ) 2). The apparent increases in oiled beach areas and masses between 2001 and 2005 reflect sampling error because no crude oil had been added to these beaches, and the high viscosity, high adhesion, and low concentration of the oil in these sediments preclude substantial diffusive spreading (10,21). For these reasons, we assumed that the actual proportion of beach area that is oiled, p, is constrained to decline monotonically with time.…”

Cytochrome P4501A biomarker indication of the timeline of chronic exposure of Barrow’s goldeneyes to residual Exxon Valdez oil

“…Exxon Valdez spill, although we recognize that as long as oil remains in the environment, some individuals are likely to encounter it (Short et al, 2006). In the case of Barrow's goldeneyes, it appears that the incidence and degree of any remaining exposure was low by 2009.…”

“…Trust et al (2000) found that Barrow's goldeneyes (Bucephala islandica), a common sea duck in the area contaminated by the 1989 Exxon Valdez oil spill, had elevated EROD activity during winter 1996-97, which was interpreted as evidence of continued exposure to lingering oil. Wintering Barrow's goldeneyes in Prince William Sound inhabit nearshore areas and forage primarily on blue mussels (Mytilus trossulus) in the intertidal zone (Esler, 2000;Koehl et al, 1982;Vermeer, 1982) where much of the residual Exxon Valdez oil persisted (Short el al., 2004;Short et al, 2006).…”

“…Some of the oil released during the 1989 Exxon Valdez oil spill has remained in intertidal sediments of Prince William Sound, Alaska over the subsequent two decades (Boehm et al, 2008;Short et al, 2004;Short et al, 2006). Estimates of the quantity remaining (Boehm et al, 2008;Short et al, 2004) represent a small fraction of the oil that originally settled on Prince William Sound beaches following the spill (Wolfe et al, 1994), with residual oil in intertidal areas estimated to exceed 50,000 kg in 2001 (Short et al, 2004).…”