Spatial variation of waterborne Escherichia coli – implications for routine water quality monitoring

Abstract

Escherichia coli are often used as faecal indicator bacteria (FIB) to provide a measure of microbial pollution in recreational and shellfish harvesting waters. However, although model forecasts for predicting the concentrations of FIB in surface waters are becoming more robust, they suffer from an inconsistency in quantification methods and an understanding of the spatial variation of FIB within a water course. The aim of this study was to investigate the transverse spatial variation in E. coli numbers (as an indicator of faecal pollution) across the estuary of the River Conwy, UK. Water samples were collected from four transverse transects across the estuary. Spatial variation of E. coli was significantly different from one side of the river to the other, although was not correlated with depth or the physiochemical properties of the water. Subsequently, microbial water quality classifications on the two opposite banks suggested very different levels of pollution coming down the river. This work has shown that the side of the river that routine water monitoring samples are taken from can make a significant difference to the classification of microbial water quality. This has important implications for sampling strategies and the use of microbial source tracking (MST) techniques.

Evaluating a microbial water quality prediction model for beach management under the revised EU Bathing Water Directive

“…While the results indicate a reasonable accuracy in E. coli prediction using the real-time prediction tool, inconsistencies between measured and predicted E. coli concentrations may still occur due to model accuracy limits and the well-recognised high spatial and temporal variability inherent in observed E. coli concentrations (Boehm, 2007;Rosenfeld et al, 2006;Whitman and Nevers, 2004;Quilliam et al, 2011;Cui et al, 2013). Therefore the authors are of the view that beach managers should be judicious when interpreting results from such models for decisions regarding the public's use of bathing waters.…”

Developments in water quality monitoring and management in large river catchments using the Danube River as an example

“…As a result, there is limited evidence of good practice and lessons learned for the design of sampling regimes for complex transnational river basins. However, using experience gained in JDS 2, microbiological monitoring in JDS 3 was expanded to include source tracking and to sample at three stations across the width of the river at each sampling location (Liska et al, 2015) because significant differences in FIOs at opposite sides of a river have been shown in other studies (Quilliam et al, 2011). Unfortunately, implementing the JDS in the summer months only, with constant low flow conditions, could lead to a systematic bias to base-flow conditions (Kay et al, 2005;McKergow and Davies-Colley, 2010).…”

Faecal Coliform Levels in Mountain Streams of Winter Recreation Zones in the Cairngorms National Park, Scotland

“…Whilst this is an important point to note, the differentiation of sources was not an aim of this study. Furthermore, Quilliam et al (2011) identify major limitations with MST, particularly the fact that it does not deal well with the complexity associated with the persistence and survival of indicator species within the environment. They also raised concerns over the spatial and temporal heterogeneity within these different environments, and suggest that spatial heterogeneity can confuse attempts to identifying the source, particularly when water bodies are not well mixed.…”