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COMPARISON OF DIRECT AND INDIRECT IMPACTS OF FECAL CONTAMINATION IN TWO DIFFERENT WATERSHEDS
Citation:
LEE, Y. J. AND M. MOLINA. COMPARISON OF DIRECT AND INDIRECT IMPACTS OF FECAL CONTAMINATION IN TWO DIFFERENT WATERSHEDS. Presented at American Society for Microbiology 106th General Meeting, Orlando, FL, May 21 - 25, 2006.
Impact/Purpose:
The objective of the proposed study is to evaluate and apply fast and reproducible DNA-based technology that can detect and track fecal contamination back to its source in complex environmental matrices, including recreational and drinking water resources.
Description:
There are many environmental parameters that could affect the accuracy of microbial source tracking (MST) methods. Spatial and temporal determinants are among the most common factors missing in MST studies. To understand how spatial and temporal variability affect the level of fecal contamination in surface waters and the sensitivity of MST methods, we sampled the streams of two cattle farms located in different watersheds: cows have unrestricted access to one, while the other is affected only by runoff. Anaerobic fecal bacteria such as Bacteroides are more abundant than other indicator bacteria such as E. coli, making it a good fecal indicator in surface waters. However, it is possible that Bacteroides might persist in anaerobic sediments for extended periods of time questioning its use as an indicator of recent fecal contamination. To test this, we employed Bacteroides-specific molecular probes to detect fecal contamination in surface waters and sediments. Bacteroides signatures were detected over time in both water and sediment samples in both watersheds regardless of the type of cattle impact or the presence of runoff due to rain events. The watershed impacted directly by cow feces showed more stable and higher level of indicators than the watershed impacted only by fecal runoff. Bacteroides signatures from the watershed under indirect cattle impact suggest that this marker might survive longer than expected in the environment. Results also suggest that spatial variation is one of the most important factors affecting the applicability of the tested MST methods.