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Title: PREDICTION OF NUTRIENT LOSS IN SURFACE RUNOFF FROM AGRICULTURAL WATERSHEDS USING GLEAMS AND RZWQM MODELS

Author
item CHINKUYU, A - UNIVERSITY OF CA
item MEIXNER, T - UNIVERISTY OF CA
item Gish, Timothy
item Daughtry, Craig

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2004
Publication Date: 2/2/2005
Citation: Chinkuyu, A.J., Meixner, T., Gish, T.J., Daughtry, C.S. 2005. Prediction of pesticide loses in surface runoff from agricultural fields using GLEAMS and RZWQ. Transactions of the American Society of Agricultural Engineers. 48:585.

Interpretive Summary: Researchers have known that the quantity and quality of runoff water varies dramatically with agricultural activity and hydrogeolgic setting. In this study, observed runoff concentrations of nitrogen (N) and phosphorous (P) from two different watersheds were compared to two prominent water quality models: 1) the Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model; and 2) the Root Zone Water Quality Model (RZWQM). Surface runoff observations were from two watersheds in the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) program. One of the OPE3 watersheds has seepage zones while the other does not. Results show that regardless of hydrogeologic setting, surface runoff of N and P could not be simulated adequately when model default parameters were used. However, both models adequately simulated N runoff when site-calibrated using runoff data from a previous year. Likewise, the GLEAMS model adequately simulated P when site calibrated. This study supports the hypothesis that present water quality models cannot accurately simulate soil-water processes governing runoff, unless site calibrated, and that more research on evaluating soil water dynamics at the watershed scale is justified.

Technical Abstract: The Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) and the Root Zone Water Quality Model (RZWQM) models were used to predict nutrient losses in surface runoff from two agricultural watersheds: one with and one without seepage zones. Daily simulated nitrate-nitrogen (NO3-N)runoff losses using default and site-calibrated GLEAMS and RZWQM were compared with measured NO3-N runoff losses from the two watersheds. Daily measured and GLEAMS-simulated orthophosphorus (PO4-P) runoff losses were also compared. Results showed that GLEAMS and RZWQM were not capable of predicting NO3-N losses from surface runoff from either watershed when default parameters were used. The default GLEAMS performed poorly in predicting PO4-P surface runoff loses for both watersheds. However, site-calibrated GLEAMS and RZWQM performed relatively well in predicting NO3-N surface runoff losses from both watersheds. In addition, site-calibrated GLEAMS adequately predicted PO4-P loss in surface runoff from the watersheds with and without seepage zones. This study suggests that either GLEAMS or RZWQM models must be site calibrated in order to adequately simulate runoff of NO3-N or PO4-P.