Exxon valdez oil spill thesis
If a VEC is spatially heterogeneous, then extra care needs to be taken in selecting reference sites to be used as surrogates of the oiled site in the absence of oiling. For example, as discussed later, this issue is a problem for assessing effects of EVOS on harlequin ducks in PWS: oiled and unoiled site comparisons have been used by some researchers to conclude continuing EVOS effects, when the data seem to indicate sufficient differences before EVOS in abundances between the oiled and reference sites to explain current patterns.
Similarly, temporal scale can be important in assessing ecological effects. Obviously, given enough time, PWS or any other ecosystem will change, but our time frame for assessing ecological recovery is the period from the aftermath of the EVOS event up to the present, some 17 y later. Intrinsic time lags in the VEC recovery response may also be critical.
An important case in point is the VEC killer whale, where an acute response of increased mortality in an exposed pod may take many years to diminish because of the long life spans, low fecundity, and social dynamics of the species. By organizational scale, we refer to addressing effects on levels of organization higher than the individual except for orcas in order for there to be an ecologically significant effect; this issue is discussed in more detail elsewhere.
However, a similar issue that also relates to spatial and temporal scales is referred to here as ecological scale. By that we mean issues like deciding on the particular population or subpopulation that is appropriate to assess. For example, for the sea otter, as discussed later, 1 subpopulation on northern Knight Island may have numbers lower than 1 unpublished prespill estimate.
Even if one accepts the numbers, the issue remains whether this is the appropriate scale to assess sea otter effects from EVOS. By contrast, resident killer whales in PWS are organized into essentially permanent discrete pods, one of which was directly exposed and affected by EVOS. But the AB pod has not yet recovered, so we characterize that as a continuing ecologically significant effect from EVOS.
- Exxon Valdez Oil Spill Biography!
- radio the movie summary essay.
- daniel mellinger thesis.
- Exxon Valdez Oil Spill Disaster!
Finally, Gentile and Harwell have proposed the use of reasonable expert judgment to assess ecological significance using criteria they developed. The intent is not to rely upon rigorous or quantitative metrics for determining ecological significance because, in most cases, there are insufficient data on one or more VEC for such an exercise. Prince William Sound is a case in point: hundreds of millions of dollars have been spent in research on ecological attributes selected by the Trustees for recovery assessment, but in very few cases are there sufficient data to make a quantitative statistical assessment of the dynamics of the attribute's response since EVOS.
In the majority of cases, requiring precise quantitative metrics in order to make judgment is impractical. Further, we believe that by making the criteria and the information used to make judgments transparent, others who might reach different conclusions would have a common basis for discussion. One final point to keep in mind: there can be no absolute conclusions about ecologically significant effects.
Our approach, using multiple lines of evidence and a reasonable application of assessment criteria, we believe, allows defensible judgments to be made in the face of uncertainties, natural spatial and temporal variability, multiple stressors, and limited information. Issues related to the characterization of exposure include the following: 1. Identifying and quantifying the sources of stress, whether physical, chemical, biological, anthropogenic, or natural;. The spatial and temporal scales of exposure, including the frequency, duration, and persistence of the stressor at a given location;.
Transformations of the stressor in the environment e. Bioavailability of the stressor e. Conversely, the stressor, which results from the mobilization and release of materials constituting the source, is in direct contact with a biological receptor and is responsible for eliciting a response in the receptor.
Essay Exxon Valdez Oil Spill
Measures of exposure can include concentrations in the surrounding medium or measures of biological responses e. Assessing the significance of a chemical stressor's exposure profile in a regional ecosystem involves understanding the magnitude and distribution of sources, the spatial and temporal extent and intensity of the stressor in the environment, and its persistence and bioavailability. The objective of this approach is to address the issue of whether the residual EVO is a continuing and significant source of hydrocarbon exposure in PWS. Hydrocarbons derived from natural and anthropogenic sources are widespread in the marine coastal environments Brassell and Eglinton Petrogenic hydrocarbon sources in PWS include eroding Tertiary sedimentary rocks and associated oil seeps in the eastern GOA, commercial and pleasure vessel operations e.
Pyrogenic inputs include combustion products from burning of coal, fuel oil, and wood and atmospheric inputs from forest fires and global industrial sources Page et al.
In addition, there is a wide range of current and historic activities that release petrogenic and pyrogenic hydrocarbons into PWS, including recreation, fish processing plants, sawmills, mining, and the rupture of petroleum storage tanks during the earthquake Kvenvolden et al. Characterizing and quantifying the proportional contribution of the multiple sources and their stressors constitute a major challenge, particularly in PWS.
- book report on the boy who lost his face?
- analytical essay on silence of the lambs.
- is there a site that does homework for you.
While there has been considerable research on identifying sources, there appears to be no systematic, quantitative estimate or comparison of the total mass contributions from these sources that can be compared with residual EVO. Consequently, the wide variation and uncertainty in the mass contributions of these multiple sources to the coastal environment of PWS, particularly subtidal sediments, have made it difficult to determine their relative contributions with an acceptable degree of confidence.
At issue is the relative proportion of the sum of the natural and anthropogenic sources to the recently estimated quantity of residual EVO remaining in the intertidal and nearshore subtidal sediments. The seminal question is not whether sources of hydrocarbons from EVOS continue to exist, as clearly they do, but whether they pose a significant risk to the populations and communities comprising the PWS ecosystem.
What is needed to address this question is a comparison of the current contributions of the various sources of hydrocarbon exposure to the PWS ecosystem. Subtidal sediments —Hydrocarbons sequestered in subtidal sediments have been hypothesized to provide a continuous chronic source of contamination to the intertidal and nearshore subtidal biological communities of PWS Short et al.
Three questions regarding the contaminant composition of these sediments need to be addressed: 1 Can different prespill sources of petrogenic PAHs be identified i. Distinguishing the individual contributions among these multiple sources is essential to evaluating current and future risk. Four sources dominate the petrogenic hydrocarbon inputs to the PWS marine environment: 1. Eroding Tertiary sedimentary rocks petroliferous shales and associated natural oil seeps in the eastern GOA coast;.
Heavy Monterey fuel oil and asphalt released to the Sound in the earthquake Kvenvolden et al. A further confounding factor is the hydrocarbons from the eroding sedimentary rocks and natural seeps contain the same suite of PAH compounds found in EVOS. Further, 32 of 84 nearshore sediment samples collected from sites that had been heavily oiled in had detectable residual EVOS residues in Page et al. These results suggest that the vast majority of the approximately 4.
This contrasts with the natural petrogenic PAH background concentrations in subtidal sediments, which are present at levels in excess of 1. Where currently present, EVOS residues constitute a relatively small addition to the natural petrogenic background at specific nearshore 10—50 m locations. The importance of oil seeps and eroding petroliferous shales as primary sources of hydrocarbons in subtidal sediments has been challenged by Short et al. While there are coal particles in the sediments of PWS, their PAH and chemical biomarker contributions are overwhelmed by those of seep oil residues and organic particles e.
Huggett et al. Therefore, the dominant sources of petrogenic hydrocarbon background in benthic sediments of PWS are eroding Tertiary shales and residues of natural oil seeps Page et al. Intertidal sediments —In , a shoreline survey of 91 sites estimated the vertical distribution of oil remaining in western PWS areas that were heavily or moderately oiled in by EVOS Short et al.
The authors estimated that the beach surface area contaminated by subsurface oil in was 6.
- best american essays 5th college edition?
- glass menagerie themes essay;
- edit my thesis statement.
- Recovery Still Incomplete After Valdez Spill - The New York Times!
- organized person essay;
- Exxon Valdez 25th Anniversary: 5 Facts About the Historic Spill?
This survey also determined that the mean mass of oil per unit area of beach ranged from 0. The residual volume of oil estimated from this study represents about 0. Human activity sites —Recently, there has been an increasing awareness of the importance of sites associated with historical human activity HA sites as potential sources of hydrocarbons. Boehm et al. Assessing the relative importance of residual EVO as a hydrocarbon source —Spatial extent of contamination is one of the important lines of evidence that can be used to estimate the significance of residual EVO in PWS.
Those issues do not seem to be relevant here. The lines of evidence chosen to assess the significance of residual EVO as a hydrocarbon source in PWS include 1 the linear extent of residual oiled shoreline Wolf et al.
Exxon Valdez Oil Spill Biography: [Essay Example], words GradesFixer
Changes in the length of oiled shoreline in PWS from to are summarized in Table 1. By , only 10 km of PWS shoreline 0. Using the estimates for the residual areal extent of subsurface EVO of The presence of a source of potential chemical stressors e. Furthermore, even if there is demonstrated toxicity under the conditions of an experimental design in the lab, these observed effects must be extrapolated to the field and then placed within the larger ecological context that addresses the issues of scale and complexity.
Unlike human health, where the focus is on the individual, ecological effects must be manifested at the population level in order to raise concern except as noted previously for certain endangered or protected species, such as, in PWS, killer whales.
Therefore, we have to look at the scale, duration, intensity, and persistence of exposure to ecological systems in order to interpret the significance of hydrocarbon stress in PWS. Concentrations of EVO declined rapidly in both sediments and biota within a few years after the spill Boehm et al. In the previous sections, we identified the magnitude and spatial extent of residual sources of contamination that are critical to evaluating the importance of residual EVO. The purpose of this section is to examine multiple lines of evidence to infer the current magnitude and extent of persistent residual EVO exposure in PWS, drawing on sediment toxicity bioavailability and biomarker data.
The intent is to view these data as lines of evidence to be used to accept or reject the hypothesis that residual EVO is a continuing source of PAH exposure that continues to pose a threat to PWS biota. This toxicity test, along with sediment chemistry, has been widely used and accepted as an indicator of benthic community health Long et al.