Unusual Source Of Ocean Water Contamination
A team of California researchers may rewrite environmental textbooks after uncovering evidence that a saltwater marsh is a source of potentially hazardous fecal bacteria that is contaminating the swimming and surfing waters of one of the Golden State's most popular beaches.
The team's conclusions, which contradicts accepted environmental science theory that wetlands should purify contaminants flowing into the ocean, are reported in the June 15 issue of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
The research shows that bacteria generated in Talbert Marsh, a man-made saltwater marsh near Huntington Beach, Calif., may be partially responsible for fecal bacteria levels thousands of times over the legal limit, according to Stanley Grant, Ph.D., who led the research team from the University of California-Irvine. Grant identified droppings from resident sea gulls as the source of the contamination, which spreads from the marsh to the shallow ocean water near the beach.
"Depending on a wetland's size and water flow rates, some 4.6 million saltwater marshes in the continental United States could be affected similarly", Grant said. "Research, to that effect ,could throw those favoring the expansion of wildlife habitats for a loop -- to say nothing of the environmental scientists", he suggested.
"One scenario is that anywhere along the coast in the United States you might run into this problem," he said. "We thought there were multiple sources for the bacteria at Huntington Beach, but what we've found is that the marsh is just one of those sources. This beach is ground zero of what could be a national problem."
"Elevated fecal bacteria levels were discovered in California after a 1999 state law set uniform bacteria standards for the state's beaches and required additional water testing", Grant said. "The tests in Huntington Beach forced the beach closures. Federal legislation calling for similar standards nationwide are currently under consideration in the U.S. Congress", Grant said.
"While not ruling out the possibility of contamination from additional sources". Grant also said emanations from the marsh alone were sufficient to close the beaches. "Paradoxically, the marsh, designed as a wildlife habitat, was expected to help clean the water", he added.
Previous studies failed to find the cause of the contamination in Huntington Beach, and data from virtually all previous studies said wetlands should filter pollutants. Those studies were based on freshwater wetlands, however, which may function differently from the saltwater wetland at Huntington Beach. More information is needed on saltwater marshes.
"The irony is that we may be introducing a source of contamination where one didn't exist before," said Mark Sobsey, Ph.D., a professor of environmental microbiology at the University of North Carolina. "We're trying to help the environment, but we may also be adding to a wildlife population that can lead to pollution where we want to swim."
"The researchers found that Talbert Marsh regularly flushes millions of gallons of bird droppings into the Pacific Ocean. Its rapid flow sweeps water from the marsh into the ocean in less than 40 minutes, according to his study. A slower flow rate would likely prevent most contamination, since longer exposure to salt water and sunlight kills the bacteria", Sobsey said.
In Huntington Beach, the researchers measured more than a dozen sites and found enterococci bacteria levels up to approximately 5,700 bacteria per 100 milliliters of water. Nearly 15 percent of approximately 2,000 samples taken ranged above the 104 parts per 100 milliliter standard that requires surf zone postings.
"We have to be smarter about how we build these marshes," Sobsey said. "If they are designed so that the water goes through them very rapidly, like it does here, the chances are pretty high that you'll have the same kinds of problems. When properly designed, though, these wetlands might improve water quality."
The research cited above was funded by a grant from the National Water Research Institute with matching funds from Orange County and the cities of Huntington Beach, Newport Beach, Costa Mesa, Santa Ana, and Fountain Valley, all in California.