Environmental study design and the ability to detect impacts: studies after the Exxon Valdez oil spill

Green R., . (2003) Environmental study design and the ability to detect impacts: studies after the Exxon Valdez oil spill. [Proceedings Paper]

This is an edited extended version of an abstract of a published paper. For the original tile abstract and citation see www.int-res.com/abtracts/meps/v210/p255-283.html. Initial sampling design decisions in environmental impact studies using observational field assessments influence the ability to detect and accurately estimate impacts. The design can dictate in advance whether the study will be able to detect even large impacts that truly exist. Following the Exxon Valdez oil spill in 1989 four separate studies of effects of the spill on the intertidal biota were conducted. The SEP Shoreline Ecology Program supported by Exxon and the CHIA Coastal Habitat Injury Assessment funded by the Exxon Valdez Oil Spill Trustee Council shared a core approach of establishing a stratified random design of site selection. The Exxon-supported GOA Gulf of Alaska study and the NOAA National Oceanographic and Atmospheric Administration Hazmat Hazardous Materials study both chose to employ subjective choices of fixed sites. The studies overlapped sufficiently in geographic area shoreline habitat and biological response variables to permit comparisons among the studies showing how the different design decisions led to differences in conclusions. Despite many common goals the four studies differed greatly in : 1 sampling effort area covered per sample quadrat sample replication within sites numbers of study sites per category numbers of samplings and total areas sampled and sampling design philosophy of targeting sampling effort complete randomization vs. matched pair designs sampling frame treatment of habitat heterogeneity within sites interspersion of sites and control of shoreline treatment and oiling intensity2 statistical analysis methods analysis of covariance vs. paired designs treatment of subsamples as replicates in F-ratios logic of inferring recovery and power calculationsand 3 choice of biological response variables taxonomic level of analysis aggregating vs. splitting separate communities and scope of communities and habitats examined. The non-Exxon studies CHIA and NOAA Hazmat made several decisions to enhance detection power and in the end concluded that there were large reductions in total biotic cover of intertidal space Fucus cover museel abundance abundance of the limpet Tectura persona and a balanoid barnacle and increases in open space and abundance of an opportunistic barnacle Chthamalus dalli. In contrast the Exxon SEP study of this same habitat and geopraphic region made design choices resulting in lower power to detect oil spill impacts in most tests. The SEP study was able to detect declines only in Fucus cover and occasionally in total limpet abundance but not in total epitaunal or mussel or balanoid barnacle abundance. Unlike the results of the CHIA and NOAA Hazmat studies nost of the taxa analyzed showed apparent increases rather than decreases from oiling and shoreline treatment. The more powerful GOA and CHIA studies of impacts of oiling in the Gulf of Alaska where oil grounded 1-8 weeks later and in more weathered condition than in Prince William Sound showed more consistent and larger reductions in intertidal biota in the sheltered rocky habitat than did the SEP study. Thus the combined effects of many design decisions that reduced power to detect impacts in the SEP study led to failure to demonstrate large impacts of the spill documented by other studies of the same habitat in the more remote region as well. In summary design made at the beginning of an impact study can influence the outcome. Decisions which increase or lower power to detect biological responses to impact may be conscious or unconscious but in the litigious atmosphere which often surrounds such studies in the aftermath of a major accident there is often divergence in study designs and corresponding divergence in study conclusions.

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Abstract

This is an edited extended version of an abstract of a published paper. For the original tile abstract and citation see www.int-res.com/abtracts/meps/v210/p255-283.html. Initial sampling design decisions in environmental impact studies using observational field assessments influence the ability to detect and accurately estimate impacts. The design can dictate in advance whether the study will be able to detect even large impacts that truly exist. Following the Exxon Valdez oil spill in 1989 four separate studies of effects of the spill on the intertidal biota were conducted. The SEP Shoreline Ecology Program supported by Exxon and the CHIA Coastal Habitat Injury Assessment funded by the Exxon Valdez Oil Spill Trustee Council shared a core approach of establishing a stratified random design of site selection. The Exxon-supported GOA Gulf of Alaska study and the NOAA National Oceanographic and Atmospheric Administration Hazmat Hazardous Materials study both chose to employ subjective choices of fixed sites. The studies overlapped sufficiently in geographic area shoreline habitat and biological response variables to permit comparisons among the studies showing how the different design decisions led to differences in conclusions. Despite many common goals the four studies differed greatly in : 1 sampling effort area covered per sample quadrat sample replication within sites numbers of study sites per category numbers of samplings and total areas sampled and sampling design philosophy of targeting sampling effort complete randomization vs. matched pair designs sampling frame treatment of habitat heterogeneity within sites interspersion of sites and control of shoreline treatment and oiling intensity2 statistical analysis methods analysis of covariance vs. paired designs treatment of subsamples as replicates in F-ratios logic of inferring recovery and power calculationsand 3 choice of biological response variables taxonomic level of analysis aggregating vs. splitting separate communities and scope of communities and habitats examined. The non-Exxon studies CHIA and NOAA Hazmat made several decisions to enhance detection power and in the end concluded that there were large reductions in total biotic cover of intertidal space Fucus cover museel abundance abundance of the limpet Tectura persona and a balanoid barnacle and increases in open space and abundance of an opportunistic barnacle Chthamalus dalli. In contrast the Exxon SEP study of this same habitat and geopraphic region made design choices resulting in lower power to detect oil spill impacts in most tests. The SEP study was able to detect declines only in Fucus cover and occasionally in total limpet abundance but not in total epitaunal or mussel or balanoid barnacle abundance. Unlike the results of the CHIA and NOAA Hazmat studies nost of the taxa analyzed showed apparent increases rather than decreases from oiling and shoreline treatment. The more powerful GOA and CHIA studies of impacts of oiling in the Gulf of Alaska where oil grounded 1-8 weeks later and in more weathered condition than in Prince William Sound showed more consistent and larger reductions in intertidal biota in the sheltered rocky habitat than did the SEP study. Thus the combined effects of many design decisions that reduced power to detect impacts in the SEP study led to failure to demonstrate large impacts of the spill documented by other studies of the same habitat in the more remote region as well. In summary design made at the beginning of an impact study can influence the outcome. Decisions which increase or lower power to detect biological responses to impact may be conscious or unconscious but in the litigious atmosphere which often surrounds such studies in the aftermath of a major accident there is often divergence in study designs and corresponding divergence in study conclusions.

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Item Type:	Proceedings Paper
Additional Information:	Summary only En
AGROVOC Term:	PETROLEUM
AGROVOC Term:	POLLUTION
AGROVOC Term:	WATER
AGROVOC Term:	ENVIRONMENTAL IMPACT
AGROVOC Term:	ENVIRONMENTAL IMPACT ASSESSMENT
AGROVOC Term:	ENVIRONMENTAL PROTECTION
AGROVOC Term:	ENVIRONMENTAL TEMPERATURE
AGROVOC Term:	POLLUTION CONTROL
AGROVOC Term:	BIOLOGICAL ANALYSIS
AGROVOC Term:	MALAYSIA
Geographical Term:	MALAYSIA
Depositing User:	Ms. Norfaezah Khomsan
Last Modified:	24 Apr 2025 05:27
URI:	http://webagris.upm.edu.my/id/eprint/16112

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