Phosphorus contributions from pastured dairy cattle to streams of the Cannonsville Watershed, New York

Accelerated eutrophication of surface waters due to phosphorus loadings from livestock agriculture is a widespread water quality problem and is of particular concern in the Cannonsville Watershed located in southeastern New York. This study sought to quantify fecal phosphorus contributions to streams from pastured dairy cattle in the Cannonsville Watershed by extrapolating field observations of cattle behavior on four farms. Pastured dairy herds with stream access were observed over four intervals during the spring and summer of 2003. Cattle behavior, including in- and near-stream deposition of feces, were recorded and manure samples collected from each herd for nutrient analysis. Patterns of fecal deposition within a pasture were related to the number of cattle and amount of time cattle spent in particular areas. The rate of in-stream fecal deposition was significantly higher than in other areas of the pasture. Fecal phosphorus deposition in other pastures of the Cannonsville Watershed was modeled as a function of number of cattle, time in pasture, and type of dairy cow (heifers vs. milk cows). Spatial databases of streams, pasture boundaries, and livestock characteristics were used to predict phosphorus deposition in pastures with stream access on approximately 90 percent of the dairy farms found in the Cannonsville Watershed. We estimate that the 11,000 dairy cattle in the Cannonsville Watershed deposit approximately 2,800 kg (6,200 lbs) of phosphorus directly into pasture streams and 5,600 kg (12,300 lbs) of phosphorus within 10 m (33 ft) of a pasture stream. At this magnitude, phosphorus loadings represent a significant environmental concern, with in-stream deposits by pastured cattle equivalent to approximately 10 percent of watershed-level phosphorus loadings attributed to agriculture. Recent efforts to exclude pastured cattle from streams as part of the Conservation Reserve Enhancement Program (CREP) were estimated to have already reduced in-stream deposition of fecal phosphorus by 32 percent. Results highlight the importance of excluding pastured cattle from streams in controlling nonpoint source phosphorus pollution.