Bacteria Runoff BMPs for Intensive Beef Cattle Operations
K. Wagner, L. Redmon, T. Gentry
According to the 2008 Water Quality Inventory and 303(d) List, 291 of the 516 impairments (i.e. 56%) were the result of excessive bacteria. Modeling and bacteria source tracking has identified grazing cattle as a source of this bacterial contamination. To help address this, the Natural Resources Conservation Service (NRCS) funded this project to evaluate the effect of stocking rate on pathogen transport from beef cattle operations and develop guidance for landowners on restoring water quality.
The project included three tasks: (1) Project Coordination and Administration, (2) Assess Bacteria Runoff from Intensively Managed Beef Cattle Operations, and (3) Technical Transfer. Task 1, Project Coordination and Administration, consisted of the Texas Water Resources Institute (TWRI) preparing and submitting eleven quarterly progress reports and the final project report, holding 25 coordination meetings, and submitting 12 invoices.
To evaluate the impact of grazing management on bacterial runoff (Task 2), TWRI and Texas AgriLife Extension Service (AgriLife Extension) installed three 1-hectare watershed sites at the Texas A&M University Beef Cattle Systems Center (BCSC), located near College Station. Sites were bermed and equipped with 90o v-notch weirs, ISCO® samplers with bubble flow meters, and a rain gage. TWRI and AgriLife Extension maintained these watershed sites for two years, conducting over 30 site visits.
A variety of stocking rates were evaluated. Site BB1 was ungrazed. Site BB2 was stocked at typical stocking rates (SR) for the area (i.e., 3-4 acres per animal unit [AU]). Site BB3 was stocked at a rate twice that of site BB2. Over the course of the project, six grazing treatments were conducted at sites BB2 and BB3.
From November 2008 through October 2010, TWRI and AgriLife Extension assessed bacterial concentrations and runoff volume from the watershed sites. E. coli concentrations at all sites greatly exceeded Texas Water Quality Standards. Even at the ungrazed site, non-domesticated animals (i.e., feral hogs) and wildlife significantly impacted E. coli levels preventing attainment of water quality standards, thus indicating the difficulty in achieving standards during runoff events due to background loadings. Data also indicated moderate stocking does not significantly increase E. coli levels above background levels and suggests that 67-85% reductions in E. coli levels may be achieved by converting from heavy to moderate stocking rates. It was also found that pastures stocked heavier than 10 acres per AU should be the primary focus of implementation efforts in this and similar environments. Our data indicated (1) stocking at rates heavier than 10 acres per AU (as is much of the improved pastureland in Texas) may increase E. coli concentrations in runoff while (2) stocking at rates less than 10 acres per AU (much of the rangeland in Texas) does not yield higher E. coli levels than ungrazed pastures. Finally, data show that runoff events occurring while the sites were stocked or within two weeks of them being stocked produced the highest E. coli concentrations; thus, it is recommended grazing in creek pastures be deferred during rainy periods. Within two weeks of grazing, E. coli levels had fallen substantially and after 30 days, E. coli values had declined to background levels.
The findings and recommendations regarding appropriate stocking rates/grazing management to minimize bacterial runoff into surface waters of Texas are being included in a fact sheet, presentation, and other resources that will become part of the Lone Star Healthy Streams Beef Cattle Resource Manual.
Throughout this project a series of educational programs conducted through the Lone Star Healthy Streams Program transferred information regarding bacterial runoff and conservation practices for reducing it to livestock producers at over 60 programs around the state. Additionally, the website reached 1,038 unique visitors since its inception. These programs have increased awareness of bacterial runoff from beef cattle grazing operations and conservation practices designed to reduce bacterial loading to Texas streams and water ways.
Much work remains to be done. The applicability of water quality standards during runoff events should be evaluated in light of the findings of this study; more data is needed to evaluate the impact of stocked pastures on bacterial runoff; work is needed to assess the impacts of continuous grazing on E. coli runoff; and transfer of this information to cattlemen throughout Texas must continue.