In : Perspectives on the Marine Environment , Proceedings from a Symposium on the Marine Environment of Southern California ,

Many twes of environmental impact asses~nt studies aim to detect effects of localized impacts. Most of the assessment (or compliance monitoring) designs uscd in such studies fail to distinguish effects of anthropogenic . ersus natural origins. and thus might lead to incorrect interpretations. The Before-AfterControl-Impact-Paired (BACIP) design surmounts this and other problems. }et has rarely been used in assessment studies. For the past three }ears. ~e ha\e used BACIP to study possible effects of nearshore discharge of produced water. an aqueous waste generated during oil production. Results from po~r analyses suggest that environ~ntal impacts are more likely to be detected for physical and chemical par~ters than for biological measures; ~thin biological parameters. effects on individualbased propenies (e.g. growth. fecundity) are more likely to be detected than changes in population densities. Ho~. er. regulatory agencies and resource managers ultimately are concerned ~th impacts on populations and communities. Our results emphasize the need to: (i) collect adequate (time-series) data before a localized penurbation begins. (ii) understand mechanisms that lead to population change and (iii) de.elop comprehensi.e models of processes leading to eD\ifonmental impacts. ,. ~ INTRODUCTION . ;" There continues to be considerable debate regarding localized effects of anthropogenic disturbances on marine biotic resources. Controversy arises. in part. from equivocal data obtained from poorly designed environmental assessment studies. Despite great efforts to obtain reliable information. most assessment designs currently in use fail to provide rigorous and convincing tests of possible effects [I]. Most of these studies fall short because the assessment designs employed do not separate changes in ecological systems caused by the putative impact from changes resulting from natural spatial and/or temporal variation [1.2. 3.4]. Consequently. it is often difficult to draw scientifically defensible conclusions about the existence or magnitude of a localized environmental impact. Even when seriously flawed, many assessment designs may be sufficient to "demonstrate"large, severe impacts. However, such dramatic (qualitative) changes in marine ecosystems are unlikely to be common due to regulatory steps such as strict permitting conditions and relatively stringent monitoring of effluents. Of more con76 Southern California Sea Grant cern are long-term chronic effects. which can involve quantitative changes ( e.g. reductions in population abundance) and which can accrue slowly. By their nature. chronic impacts are more insidious. less easily isolated from natural variability. and therefore demand more rigorous assessment designs to detect. Few assessment studies have used such rigorous designs. and as a result. regulatory agencies typically lack the sufficient scientific information to make environmentally sound decisions concerning management of marine resources. In this paper. we begin by discussing the goal of environmental assessment studies. and then illustrat~ how the three most commonly used assessment designs fail to satisfy these goals. We review an alternate design. which controls for many types of natural spatial and temporal variation and therefore provides a more defensible approach to environmental impact assessment. This alternate design reduces the possibility of wrongly concluding that an impact has occurred. However. a concern generic to all assessment designs -that actual impacts might go undetected -still remains whenever statistical power is low. We consider the issue of power. and suggest that the ability to detect actual effects may vary systematically with the type of parameter measured. These results have fundamental implications for interpreting results of all assessment studies. We illustrate many of our points with data from our ongoing study of possible environmental effects of nearshore discharge of "produced water. on benthic marine organisms. Produced water is an aqueous waste generated during oil production. and is contaminated with various petroleum hydrocarbons. heavy metals and other inorganic chemicals. as well as additives (including biocides) introduced to increase the separation of produced water from crude oil [5.6]. Since January 1988. we have been conducting a detailed study to assess whether environmen! :11 impacts result from the discharge of produced water. The system we focus on is:1 soft-bottom community occurring near Gaviota. California at a bottom depth ofappro~:1tely 25 m. Although the produced water study is specific in its primary intent. the message of this paper is relevant to the study of localized environmental impacts in general. THE GOALS OF ENVIRONMENTAL IMPACT ASSESSMENT In general. the question to be :1nswered byan assessment study of :1 localized perturbation (e.g., wastewater discharge) is: . How does the ecosystem at the site of perturbation differ from the ecosystem that would have existed had the perturbation never occurred? Obviously, the answer cannot be obtained by dire,"'t observation. and the goal of an assessment design should be to estimate the state of the system that would have existed in the absence of the perturbation [7]. Further, this estimate should be statistically compared to the observed condition (in the presence of the perturbation) and a probability should be assigned that the estimated effect might have arisen by chance ( i.e., due to natural variability in the :1bsence of an impact). If a statistically significant result is not obtained. it is absolutely '"Titical to estimate the . 'power" of the test, which is the probability that the an:1lysis could have detected an impact had it occurred. Environmental Assessment Studies 77