Nearly 85 percent of the 29 million gallons of petroleum that enter North American ocean waters each year as a result of human activities comes from land-based runoff, polluted rivers, airplanes, and small boats and jet skis, while less than 8 percent comes from tanker or pipeline spills, says a new report from the National Academies' National Research Council. Laurel Saito, an assistant professor in the Environmental and Resource Sciences Department in the College of Agriculture, Biotechnology and Natural Resources, was a consultant to the report and helped calculate the land-based sources of oil pollution to the sea.

&#8220The land-based sources are turning out to be a pretty big contribution,&#8221 Saito says, noting that this finding runs contrary to the popular belief that devastating oil spills such as the 1989 Exxon Valdez tragedy – some 10.8 million gallons crude oil spilled into Prince William Sound in Alaska after the tanker grounded on a reef – are the largest source of oil pollution in the world's oceans.

However, she notes that the data are still limited and more and better monitoring is needed: &#8220We need to set up dedicated monitoring sites on all major rivers that have significant urban development in their watersheds.&#8221 The rivers should be monitored for petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAH), which are known to be toxic to aquatic organisms and also are suspected carcinogens. These pollutants come from combustion of petroleum products.

To better monitor how much oil consumers and industry are depositing in the ocean, federal agencies should work with state and local environmental bureaus to develop a system for documenting sources of runoff, the report says. In addition, the U.S. Environmental Protection Agency should continue efforts to phase out older, inefficient two-stroke engines, which power many jet skis and other small watercraft, Saito says.

&#8220If we just switched to four-stroke engines instead of two-stroke engines, which burn fuel less efficiently, we would cut down the load significantly,&#8221 Saito says.

Together, land runoff and recreational boating account for nearly three-quarters of the 25 million gallons of petroleum released into the sea annually through the consumption of petroleum alone. More than one-half of the land-based oil contamination along the North American coastline occurs between Maine and Virginia, where there are many cities, refineries, and locations of high energy use.

Another 20 percent of the land-based petroleum reaching the sea ends up in the Gulf of Mexico.

Inland watersheds such as those that are part of the Colorado River basin in southern Nevada can be significant contributors to ocean pollution, because the majority of rivers and lakes ultimately drain into the sea. Lake Tahoe is a notable exception.

&#8220Oil spills can have long-lasting and devastating effects on the ocean environment, but we need to know more about damage caused by petroleum from land-based sources and small watercraft since they represent most of the oil leaked by human activities,&#8221 said James M. Coleman, chair of the committee that wrote the report, and Boyd Professor at Louisiana State University.

The committee found that the accuracy of the data used was much improved since the Research Council's last assessment in 1985, and the amount of petroleum released to North American and global waters was actually less than previously thought. At the same time, however, new studies show that the environmental effects of a major oil spill are longer lasting than once thought, and even small amounts of petroleum can seriously damage marine life and ecosystems.

Worldwide, about 210 million gallons of petroleum enter the sea each year from the extraction, transportation, and consumption of crude oil and the products refined from it, with an additional 180 million gallons coming from natural seepage. The study was sponsored by the U.S. Minerals Management Service, U.S. Geological Survey, U.S. Department of Energy, U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration, U.S. Coast Guard, U.S. Navy, American Petroleum Institute, and the National Ocean Industries Association. The report "Oil in the Sea: Inputs, Fates, and Effects" is available on the Internet.

Saito earned a doctorate in civil engineering from Colorado State University in 1999. Her appointment at Nevada began in February.

By Melanie Supersano, (775) 784-7030; <a href="mailto: msupersano@adv.unr.edu"> msupersano@adv.unr.edu</a>