Indicator Organisms Associated with Stormwater Suspended Particles and Estuarine Sediment

This study examined the fate of indicator organisms (fecal coliform, E. coli, and enterococci) from urban stormwater runoff associated with estuarine sediments and stormwater suspended particles. The research found a significant increase of fecal coliform, E. coli, and enterococci in the estuarine sediments at study sites following a given stormwater event. The sedimentation mechanism was linked to an increase in indicator organisms in the estuarine sediments. These indicator organisms attached to stormwater suspended particles, which then settled to the bottom sediment. A higher percentage of attachment onto stormwater suspended particles was observed for E. coli as compared to enterococci and fecal coliform. Among the three organisms, enterococci preferentially attached to the particles with diameters from 10 μ m to 30 μ m, while fecal coliform and E. coli had a broader distribution. Estuarine sediments were found to prolong survival of indicator organisms for at least seven days prior to reduction to background levels.

Keywords:

• E. coli
• Enterococci
• Sedimentation
• Suspended particles.

ACKNOWLEDGMENT

This project was financed by a grant from the Lake Pontchartrain Basin Foundation through the U.S. Environmental Protection Agency.

Notes

*Basis on the ASTM classification system: Sand particle size is greater than 0.075 mm. Silt particle size rates from 0.005 mm to 0.075 mm. Clay particle size is less than 0.005 mm.

*Average concentration of duplicate tests with standard deviation.

**Percent of adsorption rate.