INDICATOR BACTERIA CONCENTRATIONS OF TWO NORTHWEST ARKANSAS STREAMS IN RELATION TO FLOW AND SEASON
1997
Concentrations of indicator bacteria such as fecal coliform (FC) and fecal streptococcus (FS) are often used
to assess the suitability of waters for their intended use(s) and to allocate resources for water quality improvement
measures. There is evidence, however, that concentrations of FC and FS can be influenced by variables such as season
and flow rate during sampling, which could lead to biased results. The objective of this study was to assess the impacts of
season and flow rate on concentrations of FC and FS. Fecal indicator bacteria concentrations were measured for
approximately three years at five sites on two Northwest Arkansas streams. Flow data were collected at two of the five
sites. Land use in the basins draining the streams was primarily pasture (57-90%) and forest (6-40%). Significant
seasonal influences on FC and FS concentrations were detected for all sampling sites, with the highest concentrations
occurring in summer. On the two sites with flow data, flow rate generally had a significant effect on FC and FS
concentrations during all seasons, with FC and FS concentrations increasing with flow rate. Ratios of FC and FS, which
have been used in the past to differentiate between animal and human sources of fecal pollution, did not appear to
reliably indicate the major sources of fecal indicator bacteria. The findings of this study suggest a potential for fixed
sampling intervals to contribute to biased results. The issue of biased results might be avoided by sampling during times
of year and flow conditions that support the intended use(s) of the waters.
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