What are the sources of bacteria in your watershed? They may not be what you expect

Why Study Bacteria in Water?

According to the 305(b) report, the majority of waterbodies in the US do not meet established water quality standards. Over half (51%) of river miles assessed in 2010 were impaired. Pathogens are the leading cause of water quality impairment in rivers and streams of the US, impairing 16% of river/stream miles assessed. Computer models used to assess bacteria sources and loads in impaired watersheds are generally able to attribute loadings to specific land uses or in some cases specific animal categories based on known or estimated animal population numbers and fecal production rates. To provide better data on the predominant animal sources of bacterial impairments, Texas initiated a bacterial source tracking (BST) program in 2003.

What did we do?

Texas BST program uses a combination of two methods, ERIC PCR and riboprinting. To support this program, Texas assembled an E. coli BST library consisting of more than 1,600 E. coli isolates collected from over 1,400 different samples and representing in excess of 50 animal classes. Using this library, comprehensive BST has been conducted in dozens of watersheds across the state (Figure 1) to date.

Figure 1. Locations of BST projects in Texas

Figure 1. Locations of BST projects in Texas.

What have we learned?

Throughout these studies, wildlife contributions have been found to be the predominant source of bacteria (Figure 2) with non-avian wildlife being a primary contributor. Similarly, recent evaluations of small watershed and edge-of-field runoff from grazed and ungrazed pasture and range land have found background loading – loadings from wildlife and naturalized soilborne E. coli – to be significant.

Figure 2. Summary of ten Texas BST study findings.

Figure 2. Summary of ten Texas BST study findings.

This background loading is not currently adequately addressed in most water quality models, total maximum daily loads, or other water quality management efforts. This can have serious implications to application of water quality standards, particularly when applied to storm events where background runoff naturally exceeds water quality standards, as well as to TMDLs and other watershed based plans where ignoring background concentrations may lead to inaccurate load allocations and reductions as well as incongruence of modeling and BST results.

Future plans:

Future plans include working to identify the “unidentified” by continuing to expand the species in the BST library. Additionally, work is ongoing to evaluate naturalized soil borne E. coli and better evaluate wildlife populations in research watersheds. The BST team is also working to improve library independent BST methods.


  • Dr. Kevin Wagner, Associate Director, Texas Water Resources Institute, klwagner@ag.tamu.edu
  • Dr. Terry Gentry, Associate Professor, Texas A&M Department of Soil & Crop Sciences, tgentry@ag.tamu.edu
  • Dr. Daren Harmel, Supervisory Agricultural Engineer, USDA-Agricultural Research Service, daren.harmel@ars.usda.gov
  • Dr. George Di Giovanni, Professor, Environmental and Occupational Health Sciences, University of Texas Health Science Center at Houston School of Public Health, El Paso Regional Campus, George.d.digiovanni@uth.tmc.edu
  • Lucas Gregory, Project Specialist & Quality Assurance Officer, Texas Water Resources Institute, lfgregory@ag.tamu.edu
  • Dr. Elizabeth Casarez, Research Associate, University of Texas Health Science Center at Houston School of Public Health, El Paso Regional Campus, Elizabeth.A.Casarez@uth.tmc.edu
  • Dr. Karthikeyan, Associate Professor, Texas A&M Department of Biological and Agricultural Engineering, karthi@tamu.edu

Additional information:

  • Di Giovanni, G.D., E. Casarez, T. Gentry, E. Martin, L. Gregory, K. Wagner. 2013. Support Analytical Infrastructure and Further Development of a Statewide Bacterial Source Tracking Library. Texas Water Resources Institute Technical Report TR-448. College Station, TX: Texas A&M University. (http://twri.tamu.edu/reports/2013/tr448.pdf)
  • TWRI Bacteria Fate and Transport website- http://bft.tamu.edu/
  • Texas Bacterial Source Tracking Library website – http://texasbst.tamu.edu/


Thanks to the Texas State Soil and Water Conservation Board for providing continued funding and support for the Texas Bacterial Source Tracking Program.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2015. Title of presentation. Waste to Worth: Spreading Science and Solutions. Seattle, WA. March 31-April 3, 2015. URL of this page. Accessed on: today’s date.