Abstract
On recreational sandy beaches, there are guidelines for the management of bacterial pollution in coastal waters regarding untreated sewage, urban wastewater, and industrial wastewater. However, terrestrial plant debris on coastal beaches can be abundant especially after floods and whilst it has rarely been considered a concern, the bacterial population associated with this type of pollution from the viewpoint of public health has not been adequately assessed. In this study, microbes associated with plant debris drifting onto Kizaki Beach in Japan were monitored for 8 months throughout the rainy season, summer, typhoon season, and winter. Here we show that faecal-indicator bacteria in the plant debris and sand under the debris were significantly higher than the number of faecal bacteria in the sand after a 2015 typhoon. When we focused on specific pathogenic bacteria, Brevundimonas vesicularis and Pseudomonas alcaligenes were commonly detected only in the plant debris and sand under the debris during the survey period. The prompt removal of plant debris would therefore help create safer beaches.
Highlights
Likely source of bacterial contamination on beaches
The amount of plant debris that drifted onto Kizaki Beach varied from 5 to 200 kg over 10 m up to the high-water line due to flooding caused by the rainfall
Vibrio is a common bacterial Genus in coastal s ubstrates[15]. These results suggest that plant debris has the highest potential to hold pathogenic bacteria on sandy beaches
Summary
Likely source of bacterial contamination on beaches. The same genotype of Enterococci identified in river water has been detected in beach seawater after flooding[22]. No study to date has investigated bacterial contamination associated with terrestrial plant debris drifting onto beaches based on continuous monitoring and bacterial florae analysis. As a model area for this study, we evaluated Kizaki Beach, which faces the Hyuganada Sea in the Pacific Ocean and borders the Kyushu District in Japan, and is an important recreational base where the 2019 International Surfing Association World Surfing Games were held. The amount of plant debris drifting onto the beach and the number of faecal-indicator bacteria in the plant debris and the sand below the plant debris were monitored. Detection of pathogenic bacteria was attempted for each sample using bacterial florae analysis targeting the 16S rRNA gene. Laboratory experiments examined the survival of bacteria due to drought stress of plant debris and regrowth after the addition of water to simulate the conditions of dry weather and rainfall
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