ARS | Publication request: GIS-BASED DELINEATION OF NUTRIENT SOURCE-AREAS WITHIN UPLAND AGRICULTURAL WATERSHEDS

Submitted to: Proceedings of the Symposium on Watershed Management
Publication Type: Proceedings
Publication Acceptance Date: August 16, 1995
Publication Date: N/A

Interpretive Summary: To manage nutrient losses from agricultural watersheds, we must develop the capability to identify the source-areas of these nutrients over the landscape and the mechanisms controlling their loss from the watershed. The nutrient phosphorous (P) is lost from agricultural watersheds by water and sediment in surface runoff and streamflow, while nitrogen (N) is lost primarily in subsurface flow and streamflow. We developed a hydrology-water quality model using a Geographic Information System (GIS) to identify the source-areas of P and N within the upland watershed setting. The model simulates storm runoff and its source areas, along with associated P loss distribution based on a commonly used, simple soil test. N loss is simulated by combining land use distribution with a built-in accumulation subroutine of the GIS. Results of these simulations suggest land management strategies for controlling both P and N loss from the watershed. To control P loss, its application and/or build-up must be controlled principally in near-stream zones. Farther away is of less concern because there is less chance of runoff occurring from these areas. Ground water recharge source-areas controlling N loss encompass most of the watershed area. In these areas, N levels must be carefully controlled, with the ideal fertilization or waste disposal strategy holding soil N at amounts needed for plant growth.

Technical Abstract: Phosphorous is lost from agricultural watersheds by water and sediment in surface runoff and streamflow, and nitrogen primarily in subsurface flow and streamflow. Development of land management strategies for water quality concerns requires consideration of the processes controlling losses of both nutrients. GIS-based methodologies have been developed for identifying source-areas of P and N within the upland watershed. Simulate P and N losses from a 7.2-km2 watershed and a 26-ha subwatershed in east-central Pennsylvania are presented and their source-areas are identified. The results are then used to indicate possible land management strategies to control P and N losses from the watershed.