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