| Cleaning Up Our Beaches -- Inside Science
Reported July 2006
BACKGROUND: A new study of 60 beaches in southern California suggests water pollution varies with the lunar cycle, reaching the highest levels when tides are ebbing during the new and full moon. The findings could help beachgoers and managers swim when the water is cleanest.
WHAT THEY FOUND: The researchers found that in the full and new phases of the moon, levels of bacteria called enterococci were higher at the vast majority of the beaches studied. During so-called "spring tides," when water levels vary the most between high and low tides, a beach is twice as likely to be out of compliance with water quality and have high levels of bacteria. Now beach managers can use the phase of the moon and the tide stage to decide whether swimmers are more or less likely to get sick while swimming. Coastal water quality is affected by numerous factors, so monitoring beach water quality can be difficult -- bacteria levels can change within minutes. Incorporating data about tidal changes into existing models gives a much more detailed analysis of those factors.
TIDES AND THE MOON: The strength of gravity depends on the distance from the source; the closer you are, the stronger the "pull" that you feel. The moon's gravity acts on the earth, but the earth is large enough that only one side of our planet -- the one nearer the moon -- feels the moon's gravity much more strongly than the side further away from the moon. In effect, the earth is "stretched" by the difference in the moon's gravity across the earth, and this gives rise to the tides. That's why there are two tidal bulges on the earth, one on the near side, and one on the far side.
WHAT ARE ENTEROCOCCI? Enterococci are bacteria found in human and animal feces. These can commonly cause urinary tract and wound infections, since the bacteria can colonize in open wounds and skin ulcers. They are among the most resistant strains to antibiotics, and serious infections often require long treatment.
HOW WATER IS TESTED: Water samples are collected weekly and analyzed specifically for high levels of bacteria, which can cause skin irritation, infections in the eyes, ears, and throat, or intestinal illness. The bacterial level is deemed unacceptable when there are more than 100 bacteria per 100 milliliters of water.
The American Society for Microbiology and the American Geophysical Union contributed to the information contained in the TV portion of this report.
If you would like more information, please contact:
Alexandria Boehm, Ph.D.
Department of Civil and Environmental Engineering
Stanford University, CA
(650) 724-9128
ali.boehm@gmail.com
American Geophysical Union
Washington, DC 20009-1277
(800) 966-2481
http://www.agu.org
American Society for Microbiology
Washington, D.C. 20036-2904
(202) 737-3600
http://www.asm.org
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