The use of Modelling to predict and assess concentrations of Enterococci sp. within the water column

For bacteria to survive within the marine water column, they must contend with several environmental factors: light, salinity, pH, Temperature and Hydrostatic pressure. In some cases bacteria enter into a ‘viable but not culturable’ (VBNC) state; the bacteria maintain a low metabolic rate and will not divide until induced by the presence of favorable conditions. This is a risky survival tactic. The dormant state makes bacteria are more vulnerable to threats; predation from surrounding phages. Some bacteria do not take the VBNC route and instead seek refuge and residence within the organic-rich sediments, settling and waiting for favorable conditions to then re-suspend into the water column.                                                                                    Gao et al. (2013) investigated the effect of the re-suspension of marine sediment bacteria: enterococci sp. on the bathing water quality in the Severn Estuary, UK. Currently the 2006 EU Bathing Directive regulates bathing water quality by using enterococci sp. as one of the  indicator organisms. Within this study the weather and tidal conditions were recorded. To test sediment-bacteria interaction a model was used, this was previously developed by the authors (Gao et al. 2011). The results indicated that concentrations of enterococci sp. were linked to sediment transport processes: deposition and re-suspension of particles (including that of marine sediment bacteria). The accuracy of this model was then tested. Using field measurements, the predictions of enterococci sp. concentrations in the Bristol Channel were subsequently supported.

This study was chosen as it demonstrates how accurate sophisticated modeling can be in quantifying the concentrations of potentially hazardous bacteria in coastal waters. The investigation also stressed the effect adverse weather conditions have on the dispersal of sediment residing bacteria. The conclusions from this study are particularly poignant as the new EU Bathing Directive plans to have all bathing waters reach a classification of ‘sufficient’ by 2015. These constructed models could play a significant role in rapid detection and monitoring of high bacterial concentrations of indicator bacteria. This would allow a swift implementation of public health warnings to bathers within affected coastal areas.                                                                                                                                                     Gao, G. Falconer, R. A. and Lin, B. (2013) Modelling importance of sediment effects on fate and transport of enterococci in the Severn Estuary, UK. Marine Pollution Bulletin. 67: 45-54.