Monday, 7 November 2005
5

Land Use Effects on Bacteria Concentrations in Six Small Georgia Watersheds.

Karin P. Lichtenstein, David E. Radcliffe, Mark Risse, Mark Bakker, James K. Bradshaw, and Peter Hartel. University of Georgia, Department of Crop and Soil Science, 3111 Miller Plant Science Building, Athens, GA 30602

There are over 600 stream, river and lake segments that have been placed on the Georgia EPD 303(b) list for TMDL development due to poor water quality. Most of these streams are listed because they violate the state standard for fecal bacteria (a geometric mean of 200 CFU/100mL). However, this standard is being questioned because there is little information on background concentrations on streams in Georgia and more research is needed to identify potential sources of bacterial contamination. Appropriate reference streams with minimum development may be a way to determine what the bacteria standard should be for impaired streams in Georgia. This study was initiated to compare bacteria concentrations in six streams of similar basin size with differing land use. Two reference streams drain areas that are entirely forested, two streams drain areas that are predominately agricultural (one dairy and the other a combination of poultry and cattle), and two streams drain areas that are in subdivisions with septic systems. Fecal coliform and Escherichia coli (or E.coli) were measured weekly from 2002 through 2005 and analyzed using the EPA membrane filtration system and IDEXX Enterolert TM system (ENT). Bacteria counts were highest at the dairy stream and lowest at the forested sites. The bacteria standard was never exceeded in the forested streams, exceeded infrequently in the subdivision streams, and exceeded most of the year in agricultural streams. It is clear that no relationship exists in any stream between bacteria and flow, turbidity, or suspended sediment concentration. The application of the membrane filtration and the IDEXX system also consistently provided higher values in E.coli than the corresponding fecal coliform counts, suggesting a need for a standard methodological approach for the enumeration of bacteria in Georgia's waters.

Handout (.pdf format, 193.0 kb)

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