Tidal Forcing of Enterococci at Marine Recreational Beaches at Fortnightly and Semidiurnal Frequencies

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• 作者：Alexandria B. Boehm and Stephen B. Weisberg
• 刊名：Environmental Science & Technology
• 出版年：2005
• 出版时间：August 1, 2005
• 年：2005
• 卷：39
• 期：15
• 页码：5575 - 5583
• 全文大小：338K
• 年卷期：v.39,no.15(August 1, 2005)
• ISSN：1520-5851

文摘

Marine beach water quality is typically monitored in earlymorning once a week without respect to tidal condition.To assess the effect of tide on this public health warningsystem, we analyzed enterococci (ENT) data from 60southern California marine beaches with differinggeomorphology, orientation, and proximity to runoffsources. ENT concentrations during spring tides weresignificantly higher (p < 0.1) than those during neap tidesat 50 of the beaches, and at the majority of these,water samples were also more than twice as likely to beout of compliance with the ENT single-sample standardduring spring tides compared to neap tides. When tide range(spring/neap) and tide stage (ebb/flood) conditions wereconsidered together, spring-ebb tides yielded the highestENT concentrations and the greatest chance of exceedingthe single-sample standard at the majority of beaches.The proximity to a terrestrial runoff source, the slope ofthe runoff source, the slope of the beach, and the orientationof the beach had minimal influence on the tidal modulationof ENT concentrations. The presence of spring and spring-ebb tide signals at such a great percentage of beachessuggests that tide should be considered in the designand interpretation of beach monitoring program data. Italso suggests that ENT delivered by tidally forced sourcesother than terrestrial surficial runoff are widespread.Possibilities include ENT-laden groundwater (saline andfresh) from the beach aquifer as well as ENT-enriched sands,decaying wrack, and bird feces near the high water line.