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SOURCES, FATES, AND EFFECTS OF SHIPBORNE GARBAGE 48 zations. In addition, the University National Oceanographic Laboratory Systems fleet has some two dozen ships, while the National Oceanic and Atmospheric Administration (NOAA) has 18 in active service, the largest government research fleet. The EPA conducts most of its oceanographic research from a single vessel. Much of the information available about this fleet comes from NOAA. Typically, a NOAA vessel spends perhaps 250 to 295 days a year away from port. A single voyage may last two or three weeks and may linger in remote locations, including special areas, where no garbage except food may be discharged overboard. These vessels operate out of home ports, although on long voyages they may visit civilian or foreign ports. No data have been collected on the garbage generated by these ships or discarded in ports. Personnel aboard NOAA research ships include uniformed officers, merchant mariners, and visiting scientists. Approximately two-thirds of the garbage generated is thought to be food and other domestic waste (Art Anderson Associates, 1993); much of it is similar to that found in landfills, because research vessels are provisioned individually for each voyage, and consumable items are purchased at local markets. Other garbage, including used scientific instruments and their packing materials, may result from research activities. FATES OF SHIPBORNE GARBAGE Before the 1987 ratification of Annex V, it was assumed widely that the garbage generated aboard vessels was tossed into the sea. In 1975, a National Research Council committee prepared an initial approximation of all potential ocean pollutants, including marine litter, based on the assumption that all vessel wastes were discarded at sea (National Research Council, 1975). Clearly, this assumption is no longer valid. Vessel garbage generally is disposed of in one of two places: at sea, or in port reception facilities. (Recreational boaters may take their garbage home, for disposal with municipal solid waste.) This section describes what is known about the fates of garbage discarded at sea. The use of port reception facilities is addressed in Chapter 5. General Observations The fate of garbage after it is discharged overboard depends on a number of factors, including whether it is loose or bagged and the physical and chemical characteristicsâparticularly the densityâof the solids (Swanson et al., 1994). Large, dense particles, such as ground glass and shredded metal, quickly sink. In areas where there is a strong pycnocline,12 small particles tend to disperse in the 12 A pycnocline is a region of rapidly increasing density in the ocean caused by a decrease in temperature or an increase in salinity. It is a stable layer, usually found beneath the well-mixed, neutrally stable surface layer.
SOURCES, FATES, AND EFFECTS OF SHIPBORNE GARBAGE 49 surface layer, while emulsified particles may remain in the water column for long periods of time. Pulped paper may tend to settle, and unpulped paper may float for a time. Little research has been completed on the degradation of paper in the marine environment (Swanson et al., 1994). Organic material may or may not sink; garbage and sewage-related discharges have been observed in windrows up to 5 kilometers long in the coastal ocean and often "wash ashore as waves of debris" (Swanson et al., 1994). Regardless of how materials are predicted to flow in the ocean, washups of some types of debris on beaches (e.g., World War II munitions that would be expected to sink to the bottom and remain there) seem to defy logical explanation. A member of the Committee on Shipborne Wastes has found numerous containers and appliances on beaches that had been weighted or holed expressly to ensure sinking. Clearly there are forces, such as oceanic currents, that influence the fate of debris in ways that have yet to be explained fully. Many materials in vessel garbage are persistent. This is obviously the case for glass, cement, brick, metals, and rigid and film plastics, but even timber, hemp, sisal, and cloth can persist for a long time. It is well known that cigarette butts persist; they have been used for decades as markers for sewage sludge deposited in sediments (Swanson et al., 1994). But plastic is the primary concern, as is reflected in Annex V regulations. This material is not only persistent, but also abundant. Plastics dominate the debris found on beaches (see Table 2-5) and in sediments. It is appropriate, therefore, to focus here on the fate of plastics. According to results of a study carried out in Panama, the time frames for the movements of plastics into and out of beach areas appear to be on the order of months or a year (Garrity and Levings, 1993). The residence time of marked items on beaches appeared to be about a year. The marked items were replaced at the same place where they were found; there was little evidence of down- shore or TABLE 2-5 Plastic Contributions to Beach Debris (% of Total Items Found)a Location Plastic Olympic National Park 98% (1,350/1,385 items) Cape Cod National Seashore 95% (1,322/1,396) Channel Islands National Park 94% (953/1,013) Canaveral National Seashore 92% (1,095/1,192) Assateague Island National Seashore 86% (395/458) Gulf Islands National Seashore 85% (681/803) Cape Hatteras National Seashore 75% (165/220) a These data were collected in 1990-1991 by the National Park Service in quarterly surveys at 36 segments of beaches in seven parks and seashores. (Data also were collected at Padre Island in Texas, but those results are not included here because a different methodology was used.) Source: Cole et al., 1992.