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Has Prince William Sound Recovered From the Spill?
Controversial, contentious, and complex, this is the $2 billion question. Our answer is a firm and unequivocal, "It depends." This is, it depends on the resources of concern and, perhaps more importantly, it depends on the definition of "recovery." In Prince William Sound, there are many different and sometimes conflicting definitions of recovery. If you ask a fisherman from Cordova, a villager from Chenega, an Exxon USA corporate attorney from Houston--and, yes, a NOAA biologist--you are likely to receive such different answers that you may wonder if they heard the same question.
Shoreline Cleanup
Left is an aerial photo of workers flushing oil from an oiled Prince William Sound beach back into the water. Flushing, sometimes with high-pressure hot water, sometimes with ambient-temperature and/or low-pressure water, was a common cleanup method used on many shorelines in Prince William Sound. Boom (a floating barrier to oil, visible in the lower part of this photo) was placed around the beach section where the cleanup crews worked, so that oil flushed from the beach could be collected, rather than escaping back into the Sound. Collected oil was skimmed from the water surface. However, in this procedure, not all the oil refloated from a shoreline could be collected and skimmed.
The immediate, or short-term, adverse effects of oil and some of the cleanup techniques are probably less arguable than is the longer-term question of recovery. It is well-documented that fresh oil can kill shoreline plants and animals, and it is obvious that aggressive cleanup methods can stress or kill, as the photos below illustrate.
Healthy and Stressed Fucus Plants
Below are photos showing healthy rockweed (Fucus gardneri) plants, and plants stressed by washing with high-pressure hot water (Fucus is a common intertidal algal species).
 | Healthy Fucus gardneri (rockweed) plants in
Prince William Sound. |
 | Heavily-stressed Fucus after washing with
high-pressure hot water. |
See the link, Northwest Bay Study Site, at page bottom for photos of a rocky beach treated with high-pressure, hot-water washing.
The most commonly held definition of recovery probably is this: return to the way things were before the spill. Simple in concept, it is also intuitive and can be judged anecdotally or experientially by people who live and work in the Sound. Unfortunately, this benchmark is also vague and hard to quantify. In the case of Prince William Sound, it is particularly difficult to apply this standard of recovery because there is little information about "the way things were" before the spill.
Moreover, things change. Even in the absence of a major disturbance like an oil spill and cleanup, the physical and biological conditions that once characterized any given site, impacted or not, are likely to shift considerably over time. Prince William Sound is a highly dynamic environment, and we note with regularity the substantial changes occurring even from year to year in the same locations.
Parallelism
The high degree of variability in the Prince William Sound environment, the special (sometimes frantic) circumstances of site selection during an oil spill, and the fairly rigorous requirements of traditional statistical methods have led us to develop and apply new ways to assess recovery at sites affected by the Exxon Valdez spill and cleanup. For example, we compare the shape and direction of plant and animal abundance trendlines to determine if they "parallel" each other, with parallelism representing one measure of recovery.
In the graph below, we see a plot of the abundance of Fucus gardneri (rockweed). In the first years following the spill, the patterns of abundance (measured as percent cover of the rocky shores) between unoiled sites and those that were oiled and washed with high-pressure hot water bore little resemblance to each other: the washed sites had much less Fucus cover immediately following shoreline cleaning. This is not terribly surprising, as we have seen from the previous photos contrasting healthy Fucus plants with plants that had been stressed and killed by the washing treatment. However, the graph shows that, despite the very noticeable short-term impacts to the rockweed, rapid increases in plant cover between 1989 and 1991 at the oiled and washed sites significantly reduced the trendline differences between those sites and the unoiled sites. In fact, from 1991 on, the patterns have been effectively the same.
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Parallelism in Fucus Cover
Analysis of parallelism in Fucus gardneri cover, 1989-1997, comparing abundance trends at (1) oiled, washed sites and (2) unoiled (control) sites. Following the rapid increases between 1989 and 1991 at the oiled and washed sites, trendline differences between the two categories of sites were significantly reduced; i.e., the trends became more parallel. |
We see similar trends for infauna, the animals living in gravel beach sediments. The following plot shows abundance over time between unoiled sites and sites that were oiled and washed. Once again, a rapid increase in abundance before 1993 was followed by an ongoing period of parallelism. However, in this case, parallelism does not also include the same levels of abundance. The graph shows that, despite a return to a trend pattern similar to that at unoiled sites, actual numbers were lower at oiled and washed sites and the two lines have not intersected. It is, therefore, a mixed message: we see one indication of recovery and one indication of non-recovery.
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Parallelism for Infaunal Abundance
Analysis of parallelism in the abundance of infauna (organisms that live in the substrate or soft sea bottom), 1990-1997, comparing abundance trends at (1) oiled, washed sites and (2) unoiled (control) sites. Despite a return to a trend pattern similar to that at unoiled sites (i.e., parallelism), actual numbers were lower at oiled, washed sites. |
Keeping all this in mind, then, what can we say about conditions in Prince William Sound? Has it in fact recovered? Strictly speaking, we cannot extrapolate the conditions we observe in the selected areas we monitor to the Sound as a whole. But for our set of sites, we in NOAA Emergency Response Division's (ERD) monitoring program have our own perspective and our own answer to the questions.
That answer is a definite, "Yes and no." On the one hand... our work in the field, laboratory, and on the frontlines of statistical theory indicate that, yes, by many criteria, a number of the intertidal communities we study can be considered recovered. Does that mean all traces of the largest spill in U.S. history are gone and the Sound is recovered? No, not necessarily.
We have seen that oil remains in Prince William Sound. The extent to which it may be having an adverse impact is subject to debate and investigation, but for some people the fact that it remains at all is evidence that recovery has not taken place.
Some of the data and results from the NOAA ERD monitoring program also show differences between unoiled and cleaned sites: as we discussed above, infauna abundance trends at unoiled and oiled/washed sites are parallel but not absolutely equal. What is the reason for this difference? It might be a fluke of nature or of the way we selected and grouped our study sites, but we are also investigating the possibility that physical changes in the sites caused by the washing process (e.g., removal of the silty material in the beaches) may be preventing convergence in abundance as noted above.
Recovery, therefore, is in the eyes, the context, and the special interests of the beholder. While it is safe to say that nearly all of us are impressed by the degree to which Prince William Sound has rebounded from the spill and its aftermath, it would also be a fairly good bet that there will be disagreement for some time on the nature and details of that rebound and how far it needs to progress for recovery to be considered complete. Based on the perspective we in NOAA ERD have gained through two decades of spill response and from the results of our intertidal monitoring program, we consider Prince William Sound to be well along the road to recovery--but not yet recovered.
For more information
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- Northwest Bay Study Site One of our study sites shortly after high-pressure, hot-water washing in 1989, and again in 1998.
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Other pages in this series
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