|Hively, Wells - Dean|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2005
Publication Date: 5/11/2005
Citation: Bishop, P.L., Hively, W.D., Stedinger, J.R., Rafferty, M.R., Lojpersberger, J., Bloomfield, J.A. 2005. Multivariate analysis of paired watershed data to evaluate agricultural best management practice effects on stream water phosphorus. Journal of Environmental Quality. 34:1087-1101.
Interpretive Summary: Water quality can be adversely impacted by agricultural nutrients. Accordingly,environmental agricultural management programs are designed to implement improved management practices that reduce nutrient loss from the agricultural landscape. Documenting the effect of improved practices is difficult, however, do to the natural variability associated with weather and hydrology. One method that has been successfully used to monitor environmental changes resulting from improved management is the 'paired watershed' experimental design. In this design stream water flow and quality is monitored in two neighboring small watersheds for several years, after which an experimental treatment (improved management practices) is implemented on one of the watersheds. By observing the change between paired watershed nutrient loads in pre-treatment and post-treatment time periods, the effect of the experimental treatment can be quantified. This study evaluated the effects of improved dairy farm nutrient management practices that were implemented on a small dairy farm located in the headwaters of the New York City water supply system. Results showed a 43% reduction in dissolved phosphorus and a 29% reduction in particulate phosphorus that were attributable to improved management, indicating that Whole Farm Planning process used by the New York CIty Watershed Agricultural Program is succeeding in reducing agricultural phosphorus loss to stream water.
Technical Abstract: Reduction of phosphorus (P) losses from agricultural watersheds is an environmental management priority in the United States, and quantifying the water quality effects of improved practices is critical to agencies responsible for water resource protection. In the watersheds of Cannonsville Reservoir, a New York City drinking water supply located in the Catskills region of New York State, a Whole Farm Planning process was used to select and implement agricultural best management practices (BMPs) on dairy farms, so as to reduce P losses and control reservoir eutrophication. A paired watershed study was established in 1993 to evaluate changes in P loading attributable to BMP implementation on a participating upland dairy farm. The BMPs improved manure management, grazing practices, and farm infrastructure. Intensive stream water monitoring provided data to calculate event P loads delivered from the 160-ha farm treatment watershed for all runoff events that occurred during a two-year pre-BMP period and a four-year post-BMP period. Statistical control for inter-annual climatic variability was provided by matched P loads from a nearby 86-ha forested watershed, and by several event flow variables measured at the farm site. A sophisticated multivariate analysis of covariance (ANCOVA) was introduced to estimate post-BMP reductions in event-based P loading, by season and overall. Statistical power and minimum detectable treatment effect were calculated. The data demonstrated overall post-BMP load reductions of 43% for dissolved P and 29% for particulate P. Changes to farm management practices and physical infrastructure clearly produced measurable reductions in event-based P loading at the small watershed scale.