Sand Island, Oahu: Assimilation Capacity at a Tropical Ocean Outfall

Municipalities of tropical oceanic islands are increasing their use of ocean outfall diffuser systems to dispose sewage. A study to document the ability of a tropical marine ecosystem to assimilate sewage is now underway at the new 75m deep outfall of Honolulu´s Sand Island treatment plant. The immediate goal of the project is to quantify the capacity of the adjacent sea floor ecosystem to assimilate settling material by constructing a mass balance budget of organic sewage-derived material that is cycled within the benthic community. The Hawaii Undersea Research Laboratory´s minisum Makali´i is being used to conduct a sampling program at very precise locations with respect to distance from the outfall structure. A unique feature of this study is surveillance of effects on deep-water hard substrates which have been generally overlooked in studies at other outfall sites.