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United States Department of Agriculture

Agricultural Research Service

Research Project: MANAGEMENT AND CONSERVATION PRACTICES TO IMPROVE WATER QUALITY IN AGROECOSYSTEMS OF THE NORTHEASTERN US

Location: Pasture Systems & Watershed Management Research

Title: Predicting phosphorus dynamics in complex terrains using a variable source area hydrology model

Authors
item Collick, Amy
item Fuka, Daniel -
item Easton, Zachary -
item Buda, Anthony
item Weld, Jennifer -
item White, Michael
item Veith, Tameria
item Bryant, Ray
item Bolster, Carl
item Kleinman, Peter

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 2014
Publication Date: March 11, 2014
Citation: Collick, A.S., Fuka, D.R., Easton, Z.M., Buda, A.R., Weld, J.L., White, M.J., Veith, T.L., Bryant, R.B., Bolster, C.H., Kleinman, P.J. 2014. Predicting phosphorus dynamics in complex terrains using a variable source area hydrology model. Hydrological Processes. DOI: 10.1002/hyp.10178.

Interpretive Summary: Excess phosphorus (P) loss from agricultural areas leads to a decline in water quality and upsets the ecological balance of major water bodies, such as the Chesapeake Bay. Reducing the loss from agricultural fields requires a good understanding of the particular sources of P loss and the means by which it is transported to waterways. Water quality models are expected to predict the timing and quantity of P loss so that watershed managers and planners are able to implement appropriate techniques to reduce the loss of nutrients from the fields. This study evaluates two versions of the Soil and Water Assessment Tool (SWAT) in a Pennsylvania watershed in order to determine which one is more effective in predicting and locating P loss. Our work shows that correctly modeling the hydrological processes as well as the nutrient transport processes is critical to accurately predicting runoff and P loss.

Technical Abstract: Prediction of phosphorus (P) loss from agricultural watersheds depends on accurately representing the processes governing P loss from agricultural watersheds and the particular transport factors facilitating loss. The Soil and Water Assessment Tool (SWAT), a model commonly used to predict runoff and P transport, traditionally simulates runoff employing the curve number (CN) method, which assumes infiltration excess runoff, although shallow soils with shallow restricting layers or perched water tables generate zones (variable source areas) of saturation excess runoff. In this study, we compare traditional SWAT to a re-conceptualized version, SWAT-VSA, which represents variable source hydrology, in a complex agricultural watershed in south central Pennsylvania. SWAT and SWAT-VSA simulated hydrology similarly (0.69 and 0.65, respectively), but SWAT-VSA outperformed SWAT in predicting P loss from the watershed after incorporating detailed farm field management in both models. Although SWAT generalized P loss (soluble P loss: 0.01 - 0.02 kg ha-1) across the agricultural fields, SWAT-VSA was able to pinpoint those fields generating higher levels of runoff as well as receiving heavier amounts of P fertilizer applications ultimately resulting in greater P loss (0.01 - 0.20 kg ha-1). This latest work with SWAT-VSA broadens its use into complex landscapes, illustrates its usefulness as a tool in nutrient management, and continues to advertise the push towards integrating hydrologic modeling with phosphorus management.

Last Modified: 3/5/2015
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