ARS | Publication request: MULTI-YEAR CHANGE IN WATER QUALITY FROM SMALL, SINGLE USE PASTURE WATERSHEDS

Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2006
Publication Date: October 11, 2006
Citation: Owens, L.B., Shipitalo, M.J., Bonta, J.V. 2006. Multi-year change in water quality from small, single use pasture watersheds [abstract]. Soil and Water Conservation Society Meeting, "Managing Agricultural Landscapes for Environmental Quality - Strengthening the Science Base". Oct. 11-13, 2006, Kansas City, MO..

Technical Abstract: Several small (<1 ha) watersheds were used in rotational grazing studies at the North Appalachian Experimental Watershed near Coshocton, OH to study the impacts of management on water quality and the length of time for the impacts to be observed. Surface runoff was sampled on an event basis and subsurface flow was sampled monthly, and analyzed for NO3-N and other nutrients. An underlying clay layer created a perched water table, and samples of shallow groundwater were taken from springs developed where the clay outcropped at the soil surface. Such return flow feeds baseflow in watersheds large enough to have continuously flowing streams. In 4 watersheds, ranging from 18 to 123 ha, baseflow was over 50% of the total annual streamflow and approximately 20% of annual precipitation. Nitrate-N transport in baseflow was 38 to 61% of the NO3-N in the total annual streamflow. Even though small, single use watersheds may not have continuous flow, they contribute to the continuous flow of larger watersheds. The N fertilization rate in a rotationally grazed, “medium fertility” area, that contained 4 small watersheds, was increased from 56 kg/ha to 168 kg/ha per year. There was very little change in the NO3-N concentrations in the shallow groundwater for 4 years. Then NO3-N levels in the groundwater began to increase and were still increasing after 10 years of the increased fertilization rate. With management changes, including discontinuation of N fertilization, NO3-N concentrations in the groundwater returned to the pre-N increase levels after 5 years. In a “high fertility” grazing area with a similar perched water table, 224 kg N/ha was applied annually. Concentrations of NO3-N increased to a greater than 10 mg/L level after 5 years. Legumes were then interseeded into the grass forage, and mineral N fertilization was discontinued. Nitrate-N concentrations in the groundwater returned to their pre-fertilization levels after about 5 years. This multi-year response of subsurface water quality to management change in small watersheds indicates that the response time for measurable change in multi-square-mile watersheds is potentially much longer.