Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Critical Source Area Control on Water Quality in An Agricultural Watershed Located in the Chesapeake Basin

Authors
item Pionke, Harry
item Gburek, William
item Sharpley, Andrew

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 1999
Publication Date: N/A

Interpretive Summary: One of the main issues facing watershed planners is how land use and its management at the small scale ties to the quality of watershed outflows. In humid hill-land watersheds, relatively small and well-defined areas typically contribute much of the nonpoint source water, sediment, P, and N exported in outflow. From a prediction, management, and control perspective, it is important that we recognize and develop the concepts, modeling tools, and sampling protocols to delineate and assess the impacts of these critical areas. These are the highest priority areas for control, treatment, and remediation within the watershed. Based on up to 30 years of experimental and monitoring data, the outflow, N, and P exported from a typical agricultural hill-land watershed in Pennsylvania was examined in terms of critical source areas. Most of the surface runoff and P export occurs from areas near the stream during the largest 5-7 storms. In contrast, nearly all the exported nitrate originated as subsurface flow entering the soil or groundwater some distance from the stream, and is mostly exported in nonstorm flow. By combining land use, hydrologic processes, and watershed position to define critical source areas, we were able to predict and identify the major source areas for P and N. We applied these ideas and techniques to our watershed and present the results as an example of this new approach.

Technical Abstract: Based on up to 30 years of experimental and monitoring data, the outflow, N, and P exported from a typical agricultural hill-land watershed in Pennsylvania is examined in terms of critical source areas. Most of the surface runoff and P export occurs from areas near the stream. About 90% of the bioavailable P exported in outflow from this watershed was generated din storm flow from stream riparian zones. Annually, most of this export occurred during the largest 5-7 storms. In contrast, nearly all the exported nitrate originated as subsurface flow entering the soil or groundwater some distance from the stream, and is mostly exported in nonstorm flow. The observed NO3 export over the long term matches up very well with the N excess computed by N balance obtained by farmer survey for the contained agricultural land. By combining land use, hydrologic processes, watershed position, and N balance information for agricultural land, the major source areas for P and N are separate, predictable, and identifiable. We apply these ideas and techniques to our watershed and present the results as an example of this new approach.

Last Modified: 10/1/2014
Footer Content Back to Top of Page