Pure and Applied Chemistry

Introduction: The use of chemical and biological agents (e.g. dispersants and bioremediation agents, respectively), as well as certain physical oil removal techniques (e.g. high-pressure, hot-water applications to oiled shorelines) during oil spill response operations requires consideration both of the gross effectiveness of such oil removal/displacement techniques and of the ecological impact of the response technique. Accordingly, the intent of response technology optimization requires the identification of suitable response agents, their application strategies, determination of mass oil removal effectiveness, and efficient coordination of alternative response strategies with conventional measures, all compared with traditional mechanical collection methods and evaluation or relative response ecological impacts. These issues often need to be examined in an experimental setting in order to acquire information required to make more effective decisions during oil spill response and cleanup operations. Controlled field studies that are designed to identify optimal response and clean-up strategies, while valuable for realism, are expensive and often difficult to implement because of regulatory barriers (Reilly et al., 1994)). Conversely, results from small scale laboratory testing do not incorporate sufficient environmental realism (variables and scale) to permit confident predictions about real-world situations. However, bounded and partly enclosed outdoor experimental units, or 'mesocosms', can closely simulate natural aquatic environments (Odum, 1984). Such test systems provide a simulation of real-world exposure without the costs of a controlled-release field study. Mesocosms can serve to bridge the gap between large-scale field experiments, with their inherent control difficulties, laboratory experiments which can be statistically replicated but suffer from a lack of environmental realism (Rodgers et al., 1996).

Mesocosms have strengths and weaknesses depending upon system design. Therefore, the type of ecological research to be conducted will dictate the choice of mesocosm design. The following discussion presents design requirements and scientific considerations for mesocosm simulations of marine environments impacted by oil spills. Two existing mesocosm systems for marine oil spill ecological research in both pelagic and nearshore environments are reviewed in some detail - the Marine Ecosystem Research Laboratory (MERL) in Narragansett, Rhode Island, and the Coastal Oil-Spill Simulation System (COSS), in Corpus Christi, Texas.