Poster: E. Coli in urban streams: Season, land use, and hydrologic drivers.
 
Belt, K. T., Readel, K. Higgins, J. and P. Groffman

 
Escherichia Coli bacteria were enumerated from weekly stream samples (2000 to 2004) in 15 streams of the Baltimore Ecosystem Study LTER using a dye-based gel plating method. There was a wide range of site mean concentrations (<100 to 116,000 organisms/100 ml) with lowest dry weather counts in the forested, forested- suburban, and agricultural reference sites (62-288 org/100 ml). Suburban/urban sites had high dry weather levels (218-5,000 org/100 ml)/(867-117,000), with highest seasonal means in the summer (3,500) and fall (2,800) and lowest in the winter (150). Although seasonal effects dominated, drought and wet periods tended to yield lower and higher numbers, respectively. Interestingly, post runoff periods yielded highly elevated E. coli concentrations. These high levels of E.coli in post runoff samples, and their ubiquitous distribution in urban catchments suggests and their high concentrations in dry weather flow suggest sources other than leaks from civil infrastructure (e.g., soils, aquatic sediments.) High dry weather concentrations in storm drains suggest groundwater or pools of material in pipes as a possible source of bacteria. Higher concentrations in summer suggest that E.coli may thrive in the warmer environments of urban areas. The finding of significant seasonal and hydrologic effects suggests that more needs to be known regarding the ecology of E. coli, especially with respect to how effective it is as an indicator organism for public health investigations.