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Simulating Pesticide Leaching and Runoff in Rice Paddies with the RICEWQ–VADOFT Model

^a Istituto di Chimica Agraria ed Ambientale, Università Cattolica del Sacro Cuore, 29100 Piacenza, Italy
^b Waterborne Environmental, Inc., 897-B Harrison Street, S.E. Leesburg, VA 20175
^c DACPA, Sezione di Scienze agrochimiche, University of Catania, Italy
^d Dipartimento Agronomia, Selvicoltura e Gestione del Territorio, Università degli Studi, Torino, Italy

View larger version (27K): [in a new window]   Fig. 1. Site map of the study area and layout of the test paddy showing the position of inlet and outlet floodgate and the piezometers (Ferrero et al., 2001).

View larger version (31K): [in a new window]   Fig. 2. Schematic of the modeled system for the RICEWQVADOFT model.

View larger version (29K): [in a new window]   Fig. 3. Simulated water flow chart of the RICEWQ and VADOFT models. 1, paddy water input including irrigation and precipitation; 2, paddy runoff; 3, evapotranspiration, 4, the bottom of the active paddy sediment layer; 5, seepage and infiltration; 6, water inflow into vadose zone of soil profile; and 7, water outflow from Soil Layer i.

View larger version (27K): [in a new window]   Fig. 4. The modeled pesticide concentration in soil water down the soil profile on 31 Aug. 1997 (129 d after treatments [DAT]) and 1998 (134 DAT). (a) seepage rate = 0.23 cm d-1(observed) and nodal point (NP) = 81 in 1997, (b) seepage rate = 0.23 cm d-1 (observed) and NP = 81 in 1998, (c) seepage rate = 0.23 cm d-1 (observed) and NP = 31 in 1998, and (d) seepage rate = 0.90 cm d-1 (estimated) and NP = 31 in 1998.

View larger version (19K): [in a new window]   Fig. 5. The predicted daily chemical leaching concentration change at the 92-cm depth in (a) 1997 and (b) 1998. Note: BT—before the treatment.

View larger version (27K): [in a new window]   Fig. 6. The predicted vs. observed daily chemical mass in paddy sediment in (a) 1997 and (b) 1998 and their standard deviation.

View larger version (20K): [in a new window]   Fig. 7. Seepage mass out of paddy sediment to vadose zone: (a) daily and (b) cumulative.

View larger version (27K): [in a new window]   Fig. 8. The paddy runoff uncertainty distribution and parameter contribution to uncertainty of the RICEWQ-VADOFT model: (a) the uncertainty distribution (400 iterations) and (b) parameter contributions to model uncertainty.