The Myriad Sources of
Even though disasters like the recent spill off the coast of Spain sometimes still occur, double-hull tankers and tougher international standards have led to a significant drop in the amount of oil spilled by ships since 1989, when the Exxon Valdez ran aground off the coast of Alaska. That's the good news. The bad news is that 29 million gallons of oil, more than twice the amount that leaked from the Valdez, still winds up in North American ocean waters each year as a result of human activity, according to a new report from the National Research Council. But instead of coming from tankers, the vast majority of this oil arrives in the sea via such sources as land-based runoff, polluted rivers, jet skis, and even airplanes that jettison fuel over the water. Typically, only about 10 percent comes from tanker and pipeline spills, or is released during the oil-drilling process.
Oil in the Sea
"The oil you see glistening on the road when it starts to rain runs off the pavement and eventually finds its way to the sea," explained Nancy N. Rabalais, a professor at the Louisiana Universities Marine Consortium and member of the committee that wrote the report. Oil runoff from cars and trucks is a particular problem in coastal regions where more roads and parking lots are being built to accommodate dramatic population growth. Oil that is in wastewater or that has been improperly disposed of also finds its way to the ocean. Two-stroke engines manufactured before 1998 discharge significant amounts of unburned fuel and can still be found on many recreational boats and jet skis. And bigger ships may release oil from their engines while in port or at sea.
Scientists studying the aftermath of the Valdez spill discovered that the environmental devastation caused by an oil spill of that magnitude lasts much longer than previously thought. Researchers have also learned, however, that the impact of an oil spill is not always proportional to its size, since even a small spill in an ecologically sensitive area can have long-term effects. And there is growing evidence that toxic compounds found in oil can adversely affect marine species even at very low concentrations.
But while scientists have gained new insight into the damage caused by an acute oil spill, less is known about how the ocean ecosystem is affected by chronic releases from land-based sources or boat engines. To learn more, a major research effort should be launched by the federal government, the report says. Such research could be aided by a closer look at how marine life is affected when oil seeps naturally into the ocean. About 180 million gallons of oil seeps into the ocean from the seafloor each year, the committee estimated.
The report says federal and state agencies should collaborate on a new system for documenting sources of runoff to better monitor how much oil is seeping into the sea. And the U.S. Environmental Protection Agency should continue efforts to phase out older two-stroke engines. Rabalais said consumers can do their part by following municipal guidelines for discarding oil and by maintaining their car engines.
The fact that most of the oil entering the ocean comes from land or small watercraft does not mean, however, that governments can ignore tanker safety since the potential is still there for a large spill, especially in regions of the world with lax safety controls, the report notes. --Bill Kearney
Oil in the Sea III: Inputs, Fates, and Effects. Committee on Oil in the Sea: Inputs, Fates, and Effects, Ocean Studies Board, Division on Earth and Life Studies, and Marine Board, Transportation Research Board (2002, approx. 446 pp.; ISBN 0-309-08438-5; available from the National Academies Press, tel. 1-800-624-6242; $54.95 plus $4.50 shipping for single copies).
The committee was chaired by James M. Coleman, Boyd Professor, Coastal Studies Institute, Louisiana State University, Baton Rouge. The study was funded 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.