NET ENVIRONMENTAL BENEFIT ANALYSIS (NEBA) OF DISPERSED OIL ON NEARSHORE TROPICAL ECOSYSTEMS DERIVED FROM THE 20 YEAR “TROPICS” FIELD STUDY1

Abstract

ABSTRACT In November 1984, non-treated Prudhoe Bay crude oil and dispersed Prudhoe Bay crude oil were intentionally released into two separate sites, representative of near shore mangrove, seagrass and coral ecosystems, as part of the TRopical Oil Pollution Investigations in Coastal Systems (TROPICS) field study in Bahia de Almirante, Panama. Data on the relative effects of non-treated crude oil and dispersed crude oil on these ecosystems (compared to a reference site) were acquired and analyzed over various periods (30 days, 3 months, and 2.6, 10, 17, 18, and 20 years). In the short term, the oil caused mortality to invertebrate fauna, seagrass beds, and corals at both sites. At the non-treated crude oil site, there was also significant mortality to the mangrove forest. Twenty-year observations and mangrove substrate core samples reveal the continued presence of oil and diminished mangrove repopulation, as well as substrate erosion, at the non-treated crude oil site. No oil was detected and no long-term impacts were observed at the dispersed crude oil and reference sites. These results provide baseline scientific data for developing a Net Environmental Benefit Analysis (NEBA) of dispersant use in nearshore tropical systems. This paper is a review of TROPICS data and its application to NEBA preparation. Data and NEBA from the 20-year TROPICS study clearly show that the use of dispersant in the near shore environment is a sound strategy for both minimizing environmental damage to tropical ecosystems and for providing the best opportunity for recovery and repopulation in this environment. Results of this work should be applicable to similar tropical ecosystems.