Water quality is a measure by
which we determine the potential for negative health impacts caused by faecal
bacteria. Bathing beaches across Europe are held to certain standards
throughout the bathing season (May-September), although the major contributing
factor is poor storm water management as this can flood sewerage systems and
cause raw sewage to enter the ocean. Some beaches have such poor water quality,
attributed mainly to poor infrastructure that local authorities must act to
reduce the health risks. One such beach in a subtropical location (the 24.8°C water
promotes growth of microbes used to the gastrointestinal environment) is Hobie
Cat in Miami. Between 2000 and 2011 Hobie Cat had >104 colony forming units
per 100ml 7% of the times tested and this high level has no point source but
many non-point sources with particular weighting being given to animal waste as
it is a dog walking beach with no anti-fouling regulations.
As could be expected the
bacterial level in sand has a direct impact on both human health and water
quality. As part of a $6.8 million renovation project, primarily to improve and
maintain access, exogenous sand was introduced as well as improvements in
storm-water management. The access road was replaced with a semi-pervious material
to reduce the amount of run-off and trash cans were moved away from the
shoreline to the parking zone, again to prevent bacteria accumulating in
garbage from being washed onto the shore. Hernandez et al., (2014) set out to test the
effectiveness of these renovations in reducing the enterococci levels in both
sediment and water. What they discovered was that enterococci levels in the new
sand were significantly lower than the old sand even 287 days after its
introduction. This was partially attributed to a recorded reduction in animal
fouling induced by the renovation. They did however find elevated levels of
enterococci at depth, i.e. in the old sand, which was thought to be from
replication of the original enterococci. Biofilm, measured by extracellular
polysaccharide content was also shown to be significantly lower in the new sand,
possibly because of changes in mineral composition. This was retained over time
so it appears that the much higher quartz content of the new sand supported
less enterococci.
As well as reductions in sand
dwelling enterococci the water quality was significantly improved with beach
advisories based on enterococci reduced by 40% and advisories based on coliform
reduced by 90%. This study provides quantitative data on how improvements to
water management leading from renovations to access can improve the quality of
water and sand thus reducing health risks. These techniques aren’t applicable
to all scenarios as some point sources may require different management techniques
but with a 50% reduction in sand bacteria levels this could provide supporting
evidence for the clean-up of other urban polluted beaches. For example, using a
sand grain that supports less biofilm may have direct impacts on the
biodiversity of the sediment but in heavily polluted areas this could be used
as a technique to reduce human health risks.
Hernandez, R. J., Hernandez, Y., Jimenez, N. H., Piggot, A.
M., Klaus, J. S., Feng, Z., … Solo-Gabriele, H. M. (2014). Effects of
full-scale beach renovation on fecal indicator levels in shoreline sand and
water. Water Research, 48, 579–91.
doi:10.1016/j.watres.2013.10.020
That's a really interesting find - like you say, it's not going to be applicable or indeed doable for many beaches, but for densely populated areas it could prove to be instrumental in increasing and maintaining high quality beaches and water quality. Trails could be run using different particle sizes and sand composition to see which is best effective. Coupled with rapid detection assays, this may be a promising technique to improve water quality, however it would only be limited to countries that were able to afford such a regeneration.
ReplyDeleteIt is true that pollution by effluence is likely to decrease with affluence so in less developed countries with poor sewage and storm water handling capabilities this new will be of little use. However I though it nicely highlighted the link between poor drainage and pollution, especially regarding the amount of flooding we've had in the UK (see last 4 months). To me it seems like a pretty logical and probably to some extent affordable solution would be better perforation, especially in car parks where a smooth surface isn't necessary. You could improve infiltration, reducing flood risk and therefore water pollution. Hopefully we will see this kind of thing implemented more in the future.
ReplyDeleteI think the deeper "old sand" retaining horrible microbes is quite interesting here - I wonder if the enterococci est. could ever be fully gotten rid of at that level, or if would matter that deep down. It would be interesting to see if other beach processes like degradation of seaweed are affected by such changes to the beach environment, or again if that would matter that much at an urban beach. If it It seems pretty good solution to me though :).
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