tion inputs dominate except where seeps occur. It should be noted that the estimates of inputs of the non-point sources have large uncertainties; thus these data indicate only the potential magnitude of the problem.

It is important to note that one of the greatest anthropogenic petroleum hydrocarbon marine polluters is the consumer. Of the total load of petroleum hydrocarbons discharged into the sea, natural seeps account for the largest load, nearly 61 percent of the total. Of the anthropogenic load, consumers account for nearly 90 percent of the discharge.

The resulting total estimated loading of PAH to the coastal ocean of North America from all sources is approximately 5,000 tonnes per year. One-half of the PAH loading comes from natural seeps, and atmospheric deposition and land-based sources account for 33 percent and 10 percent of the total PAH loading, respectively. When considering only anthropogenic sources, consumption-related activities contribute an estimated 92 percent of the PAH load. Extraction and transportation of petroleum contributes a relatively small amount of PAH to the marine environment, especially when compared to the contribution from consumption activities.

REGIONAL VARIABILITY IN INPUTS OF PETROLEUM AND THEIR SIGNIFICANCE

A major effort of the work on inputs for this report was the spatial allocation of the source loads into regions as well as into coastal and offshore waters. To highlight the differences among the sources by region, the five megaregions (i.e., the Canadian Arctic, the Atlantic coast, the Gulf of Mexico and Puerto Rico, the Pacific coast, and Alaska) are discussed in more detail.

Canadian Arctic

Inputs of petroleum hydrocarbons, in all forms, to the Canadian Arctic are extremely small. The total average annual calculated load to this area, from all sources, during the reporting period (1990-1999) was about 2,300 tonnes (or roughly 1 percent of the total load to North American waters, Table 2-5, Figure 2-12). The dominant source in the area is atmospheric deposition associated with the consumption of petroleum hydrocarbons worldwide. Spills are rare occurrences and are generally associated with tanker traffic in and around the Hudson Bay. Land-based sources make a relatively significant contribution to the coastal zone in areas where development has occurred.

The minimal level of human activity in the Canadian Arctic has resulted in relative small releases of petroleum hydrocarbons to the environment. However, as is discussed in Chapter 5, even a small release during periods of heightened biologic activity (mating, nesting, feeding) at an important site can have long-term impacts on sensitive species. Continued efforts to reduce spills of all types should be encouraged. In addition, the implications of high-latitude deposition of toxic compounds from diffuse land-based sources (whether transported by river or atmospheric processes) should be investigated.

Atlantic Seaboard of North America

The Atlantic seaboard extends from northern Canada to Florida. Table 2-6 and Figure 2-13 present the inputs for the Atlantic regions by source and location. It is very clear that consumption sources dominate the inputs and the region from Maine to Virginia has the greatest loads along the Atlantic coast. This one region has 54 percent of all the estimated land-based inputs for North America. It has the second highest inputs from recreational marine vessels. It also ranks third out of seventeen regions for inputs from tank vessel spills, with 38 percent of the inputs into coastal waters, and fourth in terms of facility spills, with nearly 30 percent of the coastal inputs. A large coastal population, high degree of urbanization, and high energy demand all contribute to these large inputs from both transportation and consumption sources. With little oil and gas production, inputs into offshore waters are dominated by atmospheric deposition. Aircraft dumping is another significant input into offshore waters along the Atlantic regions.

The elevated inputs of petroleum hydrocarbon as total petroleum hydrocarbons (TPH) and PAH, due to human activities in this portion of North America, and especially the load entering the coastal zone from land-based sources, suggest that the sensitive marine communities in these areas are at significant risk from chronic releases, as well as the long-term, sublethal exposure associated with them. The ultimate effect of this exposure remains an area of important scientific research, but greater understanding and monitoring of nonpoint sources of petroleum pollution is needed in these areas.

Gulf of Mexico and Puerto Rico

Inputs to the Gulf of Mexico and Puerto Rico are presented in Table 2-7 and Figure 2-14, and have a very different mix and loads of sources for coastal and offshore waters. Offshore, seeps dominate inputs in the Gulf of Mexico. For anthropogenic sources, the largest offshore source varies by region: around Puerto Rico and eastern Gulf of Mexico it is spills from tank vessels; in the western Gulf of Mexico it is produced water discharges followed closely by tank vessel spills; in Mexico, it is produced water. In coastal areas, once again land-based sources dominate in all regions. Despite including the Mississippi River discharge and a high concentration of coastal refineries, the western Gulf of Mexico received only 21 percent of the total inputs from land-based sources in North America. Transportation-related inputs to the western Gulf of Mexico were about 15-25 times greater than the other Gulf and Caribbean regions, and equally di



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