Boehm Alexandria B, Weisberg Stephen B
Dept of Civil and Environmental Engineering, Environmental Water Studies, Stanford University, Stanford, California 94305-4020, USA.
Environ Sci Technol. 2005 Aug 1;39(15):5575-83. doi: 10.1021/es048175m.
Marine beach water quality is typically monitored in early morning once a week without respect to tidal condition. To assess the effect of tide on this public health warning system, we analyzed enterococci (ENT) data from 60 southern California marine beaches with differing geomorphology, orientation, and proximity to runoff sources. ENT concentrations during spring tides were significantly higher (p < 0.1) than those during neap tides at 50 of the beaches, and at the majority of these, water samples were also more than twice as likely to be out of compliance with the ENT single-sample standard during spring tides compared to neap tides. When tide range (spring/neap) and tide stage (ebb/flood) conditions were considered together, spring-ebb tides yielded the highest ENT concentrations and the greatest chance of exceeding the single-sample standard at the majority of beaches. The proximity to a terrestrial runoff source, the slope of the runoff source, the slope of the beach, and the orientation of the beach had minimal influence on the tidal modulation of ENT concentrations. The presence of spring and spring-ebb tide signals at such a great percentage of beaches suggests that tide should be considered in the design and interpretation of beach monitoring program data. It also suggests that ENT delivered by tidally forced sources other than terrestrial surficial runoff are widespread. Possibilities include ENT-laden groundwater (saline and fresh) from the beach aquifer as well as ENT-enriched sands, decaying wrack, and bird feces near the high water line.
通常每周清晨对海滩水质进行一次监测，且不考虑潮汐状况。为评估潮汐对这一公共卫生预警系统的影响，我们分析了南加州60个具有不同地貌、方位以及与径流源距离的海滩的肠球菌（ENT）数据。在50个海滩，大潮期间的ENT浓度显著高于（p < 0.1）小潮期间，并且在大多数情况下，与小潮相比，大潮期间水样不符合ENT单样本标准的可能性也高出两倍多。当综合考虑潮差（大潮/小潮）和潮位阶段（落潮/涨潮）条件时，大潮落潮在大多数海滩产生了最高的ENT浓度以及超出单样本标准的最大可能性。与陆地径流源的距离、径流源的坡度、海滩的坡度以及海滩的方位对ENT浓度的潮汐调制影响极小。如此高比例的海滩存在大潮和大潮落潮信号，这表明在海滩监测项目数据的设计和解读中应考虑潮汐因素。这也表明除陆地地表径流外，由潮汐驱动的来源输送的ENT广泛存在。可能性包括来自海滩含水层的富含ENT的地下水（咸水和淡水）以及高潮线附近富含ENT的沙子、腐烂的海草和鸟粪。
