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TECHNICAL REPORTS

Landscape and Watershed Processes

Phosphorus Loss from an Agricultural Watershed as a Function of Storm Size

^a Dep. of Crop, Soil and Environmental Sciences, 115 Plant Sciences Building, Univ. of Arkansas, Fayetteville, AR 72701
^b USDA-ARS, Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Road, University Park, PA 16802-3702
^c Centre for Sustainable Water Management, Lancaster Environment Centre, Lancaster Univ., Lancaster, LA1 4YQ, UK
^d USDA-ARS, Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Road, University Park, PA 16802-3702. Mention of trade names does not imply endorsement by the U.S. Government

^* Corresponding author (Sharpley{at}uark.edu).

Received for publication July 12, 2007. Phosphorus (P) loss from agricultural watersheds is generally greater in storm rather than base flow. Although fundamental to P-based risk assessment tools, few studies have quantified the effect of storm size on P loss. Thus, the loss of P as a function of flow type (base and storm flow) and size was quantified for a mixed-land use watershed (FD-36; 39.5 ha) from 1997 to 2006. Storm size was ranked by return period (<1, 1–3, 3–5, 5–10, and >10 yr), where increasing return period represents storms with greater peak and total flow. From 1997 to 2006, storm flow accounted for 32% of watershed discharge yet contributed 65% of dissolved reactive P (DP) (107 g ha^–1 yr^–1) and 80% of total P (TP) exported (515 g ha^–1 yr^–1). Of 248 storm flows during this period, 93% had a return period of <1 yr, contributing most of the 10-yr flow (6507 m³ ha^–1; 63%) and export of DP (574 g ha^–1; 54%) and TP (2423 g ha^–1; 47%). Two 10-yr storms contributed 23% of P exported between 1997 and 2006. A significant increase in storm flow DP concentration with storm size (0.09–0.16 mg L^–1) suggests that P release from soil and/or area of the watershed producing runoff increase with storm size. Thus, implementation of P-based Best Management Practice needs to consider what level of risk management is acceptable.

Abbreviations: BMP, Best Management Practice • DP, dissolved reactive phosphorus • PP, particulate phosphorus • TP, total phosphorus • USEPA, U.S. Environmental Protection Agency

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				A. N. Sharpley, P. J. A. Kleinman, A. L. Heathwaite, W. J. Gburek, J. L. Weld, and G. J. Folmar Integrating Contributing Areas and Indexing Phosphorus Loss from Agricultural Watersheds J. Environ. Qual., June 23, 2008; 37(4): 1488 - 1496. [Abstract] [Full Text] [PDF]