Bacteria Fate and Transport

Project Workplan

Problem/Need Statement

Bacteria impairments have been and continue to constitute the bulk of individual waterbody impairments in the state. As illustrated in the 2010 Texas Water Quality Inventory and 303(d) List, 621 impairments are documented in Texas and 319 of those are attributed to bacteria. This represents roughly 51% of all impairments in the state. The Draft 2012 Texas Integrated Report will illustrate similar levels of bacteria impairments once approved further emphasizing  the need to better understand the sources and fate of bacteria in watersheds so that these impairments can be effectively addressed and managed.

Despite having been studied for several decades, many shortcomings exist in knowledge about fate and transport of Escherichia coli (E. coli) in the environment. In freshwater streams, E. coli are used as an indicator of fecal material from warm-blooded animals present in the water column. Initial assumptions were that these indicator organisms only existed in the gastrointestinal tracts of warm-blooded animals or their freshly excreted fecal material. This dogma regarding E. coli’s reliance on the intestinal tract of warm-blooded animals led to its widespread use as an indicator of fecal contamination.Recent work has shown that E. coli can persist and grow outside of their host in both soil and water (Bolster et al. 2005; Ishii et al. 2006; Habteselassie et al. 2008; Vital et al. 2008; Garzio-Hadzick et al. 2010; Harmel et al. 2010; Vital et al. 2010) thus jeopardizing their effectiveness as accurate indicators of fecal contamination.

State-wide, watershed managers are currently utilizing tools to predict the sources, population dynamics (i.e. occurrence, growth, persistence), and transport of bacteria and are subsequently planning and implementing management strategies to address bacteria loadings into a waterbody based on these available tools. Given the fact that the sources and fate of E. coli in the environment are poorly understood, these tools cannot be expected to accurately illustrate E. coli behavior much less be able to accurately illustrate how planned management practices may alter current E. coli loadings.

In 2009, the final version of the “Bacterial TMDL Task Force Report” was published culminating discussions among experts in the field of bacteria related water resources management. This report focused on describing appropriate and cost-effective ways to implement bacteria TMDLs in Texas. Additionally, the report also identified needs for further evaluations to reduce uncertainty about bacteria behavior under varying water conditions in Texas. Largely in response to this report, the “Fate and Transport of E. coli in Rural Texas Landscapes and Streams” project (TSSWCB Project 07-06) was developed to begin addressing some of the identified information needs. Results of this work illustrated that the presence, fate and transport of bacteria is highly variable. E. coli concentrations varied widely within and between species as did the kinetic growth and decay constants for E. coli from each species. Evaluations of E. coli from other animal species were identified as a critical need for future watershed bacteria studies. Additionally, environmental factor (temperature and moisture) variations were also found to significantly influence E. coli survival and growth. Future work to evaluate fluctuations in nutrient conditions under simulated ‘natural’ conditions was recommended as a way to evaluate the responseof E. coli in the water and sediment profiles to changes in stream water quality. 

This need for additional investigation is echoed in the “Bacteria TMDL Task Force Report.” The report expressly states that “studies to identify dominant environmental factors that affect bacterial transport in streams (e.g., physical and chemical composition of stream waters [pH, total suspended solids, total dissolved solids, nutrients, etc.], temperature, etc.),” are needed to better characterize the kinetic growth and decay rates of bacteria in stream environments. Additionally, the interactions of water and sediment in the stream environment are not clearly defined and need to be better understood. Contributions of wastewater and associated nutrients to stream systems further complicate instream regrowth issues and are pointed to in the “Bacteria TMDL Task Force Report” as a needed area of exploration.

General Project Description

Building upon results from TSSWCB Project 07-06 and further focusing on addressing informational needs identified in the “Bacteria TMDL Task Force Report,” this project will focus on two primary tasks: 1) evaluating the predominant water quality parameters affecting instream bacterial fate and 2) evaluating and quantifying contributing E. coli loading to designated LU/LC types. These specific tasks were selected as those that will provide the most valuable information to watershed managers and practitioners who are faced with accurately predicting and planning to manage E. coli loading in Texas Watersheds. This will be supported by education and outreach efforts that deliver project results to personnel at local, regional, state and national levels.

Instream water quality parameters affecting E. coli growth and persistence will be quantified utilizing simulated stream environments. Flow chambers will be constructed in a laboratory setting to enable selected environmental parameters to be controlled and manipulated among multiple replications of simulated instream conditions. Flow chambers will consist of water tight channels fitted with water pumps that will re-circulate water and allow flow to mimic ‘natural’ low flow conditions. The flow rate of the water pumps can be adjusted to allow for adjustments to the simulated flow conditions. Flow chambers will be filled with stream water collected from Carters Creek under various flow conditions. (see following map). Once in the flow chambers, water will be sampled at prescribed time intervals and will be evaluated to concurrently determine changes in E. coli, Dissolved Oxygen (DO), Dissolved Organic Carbon (DOC), pH, nutrient parameters (Ammonium, Nitrate, and Phosphorus) and turbidity. Individual parameter spikes will be periodically conducted to illustrate the direct impact of each parameter on E. coli growth and persistence.

Bacteria source identification will be conducted on multiple LU/LC types monitored at the USDA-ARS Grassland Research Facility in Riesel (see following map). USDA-ARS will collect 20 surface runoff samples and 25 soil samples from each of 3 established catchments in Riesel. USDA-ARS will remit samples to SAML for E. coli enumeration and BST analysis. SAML will utilize the library-dependent ERIC-RP BST technique and compare results to both a local and state-wide BST library to evaluate the sources contributing bacteria to specific LU/LCs. Camera trap arrays will be established on each LU/LC type to monitor and estimate species presence and develop species indices. Known sources of fecal material will be collected, processed and incorporated into the Texas E. coli BST Library and utilized in the library-dependent BST analysis to further support bacteria loading identification.

Delivery of project results and findings is a critical last step that will be completed through this project. Information on these topics is in high demand and ample opportunities exist to deliver findings to interested parties through focused workshops, meetings and conferences. One such avenue that results will potentially be presented at is the Texas Watershed Coordinator Roundtable. The July 27, 2011 meeting of this group focused solely on bacteria related content and this was by far the biggest audience at these roundtable events to date. The engagement of the audience clearly illustrated the desired/need for further information on bacteria related topics, especially those that will be addressed through this project. Development of peer-reviewed publications (or working drafts) is another way that education and outreach will be achieved through this project. Additionally, this provides extra credibility to the work done thus solidifying the significance of the work conducted through this project and enabling it to be more rapidly and widely utilized.

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