Occurrence of fecal and non-fecal sources bacteria during several overlap rainfall events at Fujiazhuang bathing beach in Dalian, China

With an aim to provide guidance for public health swimming in the beach, as well as provide a scientific basis for beach safety management, a continuous 16-day monitoring after the first rainfall and 6-day monitoring after the last rainfall in the swimming season in 2015 was carried out at Fujiazhuang bathing beach in Dalian to evaluate the effects of rainfall on typical fecal sources (enterococci, human specific bacteroides) and non-fecal bacteria (staphylococcus aureus) contamination. The results showed that the concentration of enterococci using culture dependent method and human bacteroides using real-time PCR always fluctuated with six overlap rainfalls, which had a severe impact on fecal bacteria indicators. During sampling period, the water quality exceeded the single sample standard for enterococci (<35 cfu/100 mL) and human specific bacteroides (<8.6 × 10² copies/100 mL) in 100% and 96% of the samples, respectively, higher concentrations were consistently distributed near the drain outlet, indicating that most of the stormwater flowed to the drainage system discharging into the marine. The fecal sources bacteria, enterococci and human specific bacteroides were significantly correlated with each other, both of them have a strong relationship with rainfall (p<0.01), while non-fecal contaminated bacterial concentration showed no correlation with rainfall (p>0.05). Swimmer density is another major factor affecting the concentration of both fecal and non-fecal sources bacteria in seawater. Considering from the public health, it is recommended to reduce the swimming frequence during continuous rainfall period, as well as to increase periodic surveying of highly frequented beaches, especially during periods of peak bather density.