Impact of Animal Waste Best Management Practices on the Bacteriological Quality of Surface Water

An extensive 10 year monitoring project was initiated in 1986 to examine the effects of a combination of BMPs on surface water quality within a watershed with complex land use. This research specifically examined bacteriological water quality and BMP impacts. Bimonthly grab samples were collected from four surface water monitoring stations, including the watershed outlet, and analyzed for fecal coliform, total coliform, and fecal streptococcus bacteria. Other data compiled from the watershed included hydrologic, meteorologic, geologic and land use data, also collected on a regular basis. Data were collected continuously throughout the project, and thus included both pre- and post-BMP monitoring data. BMP implementation included animal waste storage facilities, nutrient management plans, conservation tillage, alternative water sources for livestock, fences, vegetative filter strips, runoff diversions, and others.

Statistical analysis of the monthly precipitation data indicated no significant difference in rainfall quantity between the pre-BMP and post-BMP monitoring periods. Monthly runoff totals increased 39% from the pre- to the post-BMP periods at the watershed outlet. Increases at all of the subwatershed outlets occurred as well (B, 40%; C, 38%; D, 16%). Statistical analysis did not show a significant difference in runoff between the two monitoring periods, except at station C, where post-BMP runoff was significantly greater than the values measured during the pre-BMP period.

Overall reductions in the mean (geometric) levels of total coliform, fecal coliform and fecal streptococcus bacteria observed at the watershed outlet were 81%, 30% and 76%, respectively. Both parametric and nonparametric statistical analysis techniques were applied to the bacteriological data. Regression analysis of the fecal coliform data showed an increase during the pre-BMP period followed by a decrease post-BMP and a statistically significant difference between the two periods (p=0.004). No trends were evident. Only one of the four stations had a statistical difference between pre- and post-BMP fecal streptococcus data, however, a downward trend was present at every station. No statistically significant difference between the pre- and post-BMP total coliform bacteria was evident, although a downward trend was present at the watershed outlet. These findings indicate that the combination of BMPs implemented in the watershed were effective in reducing the loss of fecal bacteria to receiving streams via overland flow.