UC Davis Department of Plant Sciences

Sample Hold Time Analysis Livestock Management and Water Quality on US Forest Service Grazing Allotments


Contact Person: Dr. Kenneth W. Tate

Participants: Lea Kromschroeder, Donna Dutra, Rob Atwill, Scott Oneto, USDA Forest Service – Region 5, Stanislaus National Forest, Plumas National Forest, Tahoe National Forest, Shasta-Trinity National Forest, Klamath National Forest.

Comment or Questions?


Problem Addressed

One of the major logistical challenges to conducting fecal indicator bacteria (fecal coliform and indicator E. coli) sampling and analysis associated with this project is that ideally the time from sample collection until sample processing in the laboratory should be less than 8 hours. The remoteness of many interesting sample locations on national forests and wilderness areas makes meeting this sample hold time condition difficult, if not impossible. The concern is that fecal indicator bacteria (FIB) concentrations within the sample could change significantly via decay or growth between the time of collection and analysis. We conducted an experiment in late summer 2010 to evaluate the effect of sample hold time on FIB analysis of stream water.



In September 2010, we collected stream water from a sample location on the Stanislaus National Forest. We returned this sample to our lab at UC Davis. We immediately cultured indicator E. coli and fecal coliform bacteria from the original sample, and spiked a 10 liter sample of this stream water with fecal coliform and indicator E. coli to a concentration of approximately 100 cfu/100 ml. This spiked sample was immediately sub-sampled and fecal coliform and indicator E. coli concentrations determined at time equal 0 (n=4 100 ml sub-samples each for fecal coliform and indicator E. coli). The sample was held on ice to simulate conditions of storage in an ice chest. Bacteria concentrations were determined for sub-samples processed at 3, 6, 8, 12, 16, and 24 hours hold time. Linear regression statistical analysis was used to determine if a significant change (i.e., decay or growth) in either indicator occurred over the 24 hour holding period.



Figure 1. illustrates mean concentrations of fecal coliform and indicator E. coli over the 24 hour holding period. Linear regression analysis indicates no significant change in concentrations over the course of the experiment. Thus, there was no effect of hold time on the determination of cfu/100ml. These results indicate that with appropriate storage of samples on ice, analysis results for samples held up to 24 hours prior to processing should be representative of samples processed at 8 hours or less.





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