Surfers at beaches where stormwater drainage pipes discharge into the ocean risk catching more than waves on a rainy day.
By Monmouth University’s Urban Coast Institute
Monmouth University researchers studying the influence of weather and ocean conditions on microbial pollution found that within 6-24 hours of moderate rainfall, enterococcus bacteria levels exceeded state health safety standards about half the time at tested beaches. While rain is a known driver of illness-causing microbial pollution at New Jersey beaches, this was the first peer-reviewed study to formally investigate the linkage.
Endowed Professor of Marine Science Jason Adolf and Specialist Professor Jeff Weisburg of Monmouth University’s Biology Department collected water samples with students on dry days and following storms at five Monmouth County beaches with outflow pipes in 2019 and 2020. The research was conducted both in the summer bathing season when the state monitors pollution levels weekly, and in September-May, which is not regularly monitored by the state. Although the throngs of beachgoers largely vanish after Labor Day, the fall and winter months are considered prime surfing season for the Jersey Shore and its waters remain crowded with riders taking advantage of hurricane swells.
“Without a system on the beach to warn them, surfers could unknowingly be exposed to bacteria that can cause respiratory infections, nausea, abdominal pain, and fevers,” said Dr. Weisburg, whose research focus is immunology and disease. “Since the restrictions on which beaches you’re allowed to surf at are lifted in the offseason, surfers should take advantage of the other beaches open to them and steer clear of outfall pipes during and after rains.”
The samples were tested for enterococcus levels and checked for relationships with data for three important drivers: precipitation, which transports animal waste and other pollutants to beaches via stormwater discharges; water temperature, which determines how easy it is for bacteria to thrive; and tide stage, which can control whether the pollutants are diluted or concentrated.
The research found that rainfall within 6-24 hours of sampling and higher water temperatures were the best predictors of high enterococcus counts, although exceedances of the state regulatory threshold of 104 colony-forming units (CFU) per 100 mL seawater were found in all seasons – even in seas as cold as 44 degrees, following rainy periods. Although not an explicit part of this study, observations during sampling suggested that these bacteria spikes subsided quickly at these sites, within one or two days of occurring.
The researchers created a model that could predict the likelihood of bacteria spikes at the sampling sites with accuracy based on data for rainfall accumulations, water temperature, and water levels. When the model focused on sites having stormwater drainage in the surf zone, its predictions that levels would exceed the state threshold were correct 69 percent of the time; it was a perfect 100 percent when it predicted levels would stay safely below the threshold.
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