Although enterococci are often not pathogenic they are used as an indicator because they are often found to correlate with adverse human health effects. Enterococci are most commonly associated with point source sewage pollution. In recent studies beach sediments have been shown to be capable of sustaining populations of enterococci and can contribute significantly to faecal indictor numbers even in the absence of sewage runoff. This study aimed to quantify the amount enterococci present in the beach sediment and to determine if patterns observed could be used to improve preventative measures that ensure beach safety.
Samples were taken from three tidal zones (supratidal, intertidal and subtidal zones) on eight beaches in Florida in September 2010 and February 2011by taking core samples. They assessed the number of enterococci in the sediment samples and compared them with characteristic features of the sand such as: moisture content and grain size. They also compared observed numbers of enterococci in the sediments with recordings of the faecal indictor in the water as collected by the Department of Health (DOH) in previous years.
Enterococci were found in all of the beach sediments however to varying degrees of intensity. Enterococci levels were consistently higher in the supratidal zones. This was thought to be associated with on shore non-point sources. The subtidal in intertidal zones are thought to have lower levels of enterococci because they are exposed to the energy of waves which are capable of removing these bacterial deposits. There is a strong correlation between levels of enterococci in the water measured by the DOH and in the sediments. However there was a lack of correlation in the September supratidal data set but this was thought to be the result of heavy rain fall because of frequent washing of the sand. Grain size was not observed to have a significant effect on levels on enterococci. There was a negative correlation between moisture content and indictor numbers.
This study represents an important step in improving methods of beach safety management. It is one of the first studies which have assessed multiple tidal zones on beaches in a regional area. With a greater understanding of the contributors to faecal indictors on our beaches it could help us to improve early warning systems helping to prevent adverse effects on humans. By including this data it could help account for consistent variations in enterococci levels which could help to prevent unnecessary beach closures. This paper does not discuss why the enterococci are able to persist longer in the beach sediments in comparison to the water. I assume that the sediments reduce environmental pressure by offering protection against the force of water currents and are higher in nutrient deposits which would allow communities to thrive. Further studies could be conducted to monitor other parameters that might cause increases in enterococci numbers such as number of human visitors and close monitoring of weather conditions.
A review of: Phillips, M.C., Solo-Gabriele, H.M., Piggot, A.M., Klaus, J.S., Zhang, Y. (2011). Relationships between sand and water quality at recreational beaches. Water Research. 45 6763-6769
3 comments:
Interesting, maybe I have missed it, but what are the authors suggestions of the use of there sampling method? and how with such infrequent measurements of enterococci would it improve beach management? or was the research done just to prove their sampling methods are effective at estimating safety levels? Corin
Hey Corin those are some very good points.
You are right the sampling times are infrequent which could limit the reliability of the data. However a possible explanation for this could be because the bacterial communities in the sediments are capable of persisting for longer which (as the authors described) gives them a more “time averaged” input of enterococci into the water column. This slower and more consistent release would mean there could be less variation and so could make it less important to sample so frequently.
The study was conducted to contribute to our understanding of the factors involved in the inherent variation of enterococci levels generally found in water samples. Utilising this additional information is suggested to help to account for the variation of enterococci which in turn would help with beach management strategies. They also suggest that sediment samples could be useful in the identification of high risk beaches so that management efforts can be more effectively distributed.
Hope this answers your questions.
I see interesting reasoning, thanks
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