Oceanographic Studies in Support of the EPA (Environmental Protection Agency) Designation of Deep Ocean Dredged Material Disposal Sites in Hawaii,
CORPS OF ENGINEERS FORT SHAFTER HI PACIFIC OCEAN DIV
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The results of oceanographic studies conducted at deep ocean sites in Hawaii between 1976-1983 have revealed that ocean disposal of dredged materials has not had any significant adverse or long term impact on the marine environment in Hawaii. Impacts to the water column are only short term, confined to a matter of hours for each individual dump. The major water column impact is the temporary increase in suspended sediments and turbidity. The small volumes of dredged materials, the infrequent interval for disposal operations, and the relatively clean nature of the dredged materials further reduces the overall magnitude of impacts. Although the most significant impacts of disposal operations occurred to the benthic environment at the disposal sites, little long term adverse effects were noted and some beneficial effects may also have occurred. All of the deep ocean disposal sites in Hawaii are located in water depths in excess of 300m, and the benthic environment at these sites is well below the the photoic zone, thermocline, and surface mixed layer where most primary production is taking place. As a consequence, the primary sources of food to support the deep sea benthic ecosystems at the sites must directly or indirectly be carried down from shallow water, in the form of migrating fish and other nekton, drifting plankton, detritus, the carcasses of dead organisms, turbidity currents, etc. As a consequence, the biomass of the deep benthic communities is lower than what is observed in shallower water, lacking plants altogether.