July 1, 2006 By washing decomposing plants into the ocean, high tides could contribute to the increased levels of Enterococci that are often responsible for beach closures. Scientists have now established a clear link between pollution levels and lunar cycles. While lab tests usually take a day -- meanwhile exposing beachgoers to risks such as diarrhea and skin rashes -- forecasting could help authorities take preventative measures.
PALO ALTO, Calif. -- Some scientists say they can predict when beach pollution will be the worst by monitoring the moon. And that could mean safer beaches for people all over the world.
Summer at the beach ... Fun for many college students, but these Stanford students are not building a sand castle. They're trying to figure out if the beach is safe for you and your children.
"The bacteria that I'm talking about are fecal indicator bacteria, so these are the organisms that cause beach closures," Stanford environmental engineer Alexandria Boehm tells DBIS.
She says the answers may not all be below your feet. She actually looked up to gather the facts. Boehm found a correlation between beach pollution, lunar cycles, and spring tides.
"The spring tides occur during the full and new moons, so during the full and new moon, the bacteria levels are higher at the beach," Boehm says. That means beachgoers are more likely to get diarrhea, skin rashes, and sore throats.
Today, health officials must wait one day for water samples to be tested before shutting down beaches. But Boehm says by the time they put up that sign, it's one day later, and the pollution event is usually gone. She says by looking at the moon, health officials could predict when pollution will be highest without that one-day delay.
The next step in the process is Boehm finding the source of the contamination. Back at the lab, she and her students test the groundwater samples. Fluorescence means contamination.
She also says decaying plants on the sand could be the source of pollution. Since spring tides are higher, they wash further up the beach and wash more contaminants into the surf.
"It's one thing to be able to predict when beach pollution levels are going to be high, but the better thing to do would be able to know what the source is so the problem can be fixed at the source," Boehm says ... And that would mean safer beaches for everyone!
BACKGROUND: A new study of 60 beaches in southern California suggests that 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 gwet 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 ml of water.