Tracking Pollution

Ozarks Water Watch

David Casaletto published this article on the Ozarks Water Watch newsletter and let me share it on the blog. 
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Bacterial Source Tracking Needed to Determine Pollution Contributors
David Casaletto, Executive Director, Ozarks Water Watch.

I was attending a conference this summer and a presentation on Bacterial Source Tracking (BST) really got my attention.  In more laymen terms, a laboratory identifies the source of the E.coli and other bacteria that are polluting our streams and water bodies.  What really made me sit up and listen was, according to this study in Texas, 62% of the bacteria came from wildlife, while 10% was human and 13% cattle.  These were not the percentages I expected!


In Texas, there are 273 bacterially impaired water bodies.  With a nonpoint source grant, they set out to identify and assess the sources of these bacteria - E. coli, Enterococcus, fecal coliforms - in these water bodies to properly determine the risk to water recreation.  Then they would develop effective watershed restoration strategies, such as watershed protection plans (WPPs) and total maximum daily loads (TMDLs).

Bacterial sources are extensive and include all birds, wildlife, livestock, pets and humans.  Source surveys, computer models and bacterial source tracking (BST) are the primary methods for identifying predominant bacterial sources in impaired waters.  BST offers distinct advantages over computer modeling and source surveys.

Source surveys, which estimate the numbers and distributions of animals and humans in a watershed, are not capable of assessing most wildlife species or how bacteria from sources are transported to the impaired waters.  Computer modeling addresses the issues with transport; however, because wildlife populations are rarely known, models are unable to adequately assess contributions from wildlife.  BST is able to evaluate wildlife, along with other major sources, and the impacts of transport because BST uses instream water samples for its assessment.

The premise behind BST is that DNA fingerprinting and other molecular targets can identify bacterial strains specific to each animal species since each species has different diets and digestive system conditions that select for distinct strains of bacteria.  This distinction allows the original source of the fecal contamination to be identified.  But BST methods require the development of a DNA fingerprint library.


The Texas BST Library currently contains more than 1,500 E. coli isolates obtained from more than 1,300 different domestic sewage, wildlife, livestock and pet fecal samples.  These isolates, which represent more than 50 animal subclasses, were selected after screening several thousand isolates from more than a dozen different studies throughout Texas.

BST accuracy is best when identifying broad source categories and decreases as the sources are more specifically identified.  A 7-way (non-avian wildlife, avian wildlife, pets, cattle, other non-avian livestock, avian livestock, human) categorization is shown in chart to the right.



The technologies used for BST are continuously evolving and improving. BST has been tremendously helpful in identifying significant bacterial sources throughout Texas.  The state BST laboratories can provide guidance and assistance with performing BST for watersheds. I think it is time for other states to jump on the BST bandwagon.  Too many times, we "think" we know the source of the pollution is human or CAFO, when it may be wildlife.  More information on BST can be found at: texasbst.tamu.edu.
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Ozarks Water Watch is a non-profit organization dedicated to maintaining and improving the water quality of the upper White River watershed.
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