Introduction. Rice issues Environmental issues Directive needs Models lacking

Transcription

1 Second European Modelling Workshop Pesticides in Groundwater Lisbon, 6-7 June 2002 Modelling Pesticide Leaching and Runoff in Rice Paddies with the RICEWQ+VADOFT Package Ettore Capri Istituto di Chimica Agraria ed Ambientale, UCSC, Piacenza, Italy

2 Introduction Rice issues Environmental issues Directive needs Models lacking

3 Objective To evaluate a newly developed modeling approach to predict the overall pesticide fate in paddy field, including leaching in the unsaturated (vadose) zone.

4 Materials and methods Field site: the East Sesia, Italy; 2-yr field datasets ( ). Test chemical: cinosulfuron at the dose level of 39.5 and 41.5 g a.i./ha in 1997 and 1998 respectively.

5 Study area

6 Piezometer position

7 Crop practice and water management Cynosulfuron and g/a.i. ha (1997 and 1998) Preparation Paddy flood Treatment Steady water Water cycling Water renewal Sowing Dry period over crop emergence Dry period in grain formation Final dry period Harvest From Sep.1

8 Materials and methods Model release: the RICEWQ ver VADOFT Package Input files Model Package Input files RICEWQ input files Core files Interface EXESUP files Meteorological file RICEWQ VADOFT VADOFT input files Output files

9 The RICEWQ model In terms of mass balance and using a daily time step, RICEWQ model simulation involves mathematically tracking the total mass of chemical residues in three medias of rice paddy: rice foliage, water column, and benthic sediments from the point of application. That is,

10 the RICEWQ model The package apply RICEWQ version to simulate the air drift, crop interception, volatilization, pesticide decay, adsorption and transformation in paddy surface water and paddy sediment. For each process, the model has a set of linear or non-linear theory formula. The reader is suggested to refer to the RICEWQ version manual (William, 1999).

11 The leaching process simulation-- VADOFT model Below the paddy sediment, VADOFT performs one-dimensional transient or steady state simulations of water flow and solute transport in variably saturated porous media. The code employs the Galerkin finite-element technique to approximate the governing equations for flow and transport. It allows for a wide range of nonlinear flow conditions, and handles various transport processes, including hydrodynamic dispersion, advection, linear equilibrium sorption, and first-order decay.

12 Properties RICEWQ package RICEWQ ver Version Platform Windows 9x DOS Interface Yes No VADOFT Yes No Leaching Yes No Parameters Field capacity, initial soil moisture, RICEWQ and VADOFT input file RICEWQ ver input file

13 The assumption of the model package The assumption of RICEWQ Runoff Topsoil systems: 20cm Paddy water: 9-11cm Active sediment: 5cm Leaching The assumption of VADOFT The 1 st soil horizon: 5-55 cm Sub Soil Systems The 2 nd soil horizon: cm Groundwater Ground water

14 Results Summary of estimated water balance Properties Water (m 3 /ha) Percent of total paddy water output (%) Water (m 3 /ha) Percent of total paddy water output (%) Total paddy water input Total paddy water output: Evapo-transpiration Paddy water runoff Water inflow to soil profile including irrigation, rainfall and paddy water volume difference at the initial and terminal simulation.

15 The predicted vs. observed pesticide runoff (ug/l) Chemical runoff (ug/l) Measured Predicted Predicted Days after the application Seepage rate=0.23 cm d -1 ; Seepage rate=0.90 cm d -1.

16 The predicted chemical leaching concentration at cm of soil depth Concentration (ug/l) BT Concentration (ug/l) BT

17 The predicted vs. observed pesticide mass in paddy sediment Cinosulfuron mass (mg/ha) Observed Predicted Days after the application 1997 Cinusulfuron mass (mg/ha) Observed Predicted Days after the application 1998

18 The effect of seepage rate and NP value on chemical mass balance Chemical fate Predicted Predicted Predicted Chemical mass (mg/ha) % of applied rate Chemical mass (mg/ha) % of applied rate Chemical mass (mg/ha) % of applied rate Decay in paddy field Pesticide runoff Leaching to vadose zone: Storage in vadose zone Decay in vadose zone Leaching to groundwater E E E E-14 seepage rate=0.23 cm/day & NP value = 81; seepage rate=0.23 cm/day & NP value = 31; seepage rate=0.90 cm/day & NP value =31.

19 The predicted pesticide leaching concentration Concentration (ug/l) Depth (cm) Seepage rate=0.23 cm/d, NP=81 Depth(cm) Concentration (ug/l) Seepage rate=0.23 cm/d, NP=31 Depth (cm) Seepage rate=0.90 cm/d, NP=31 Concentration (ug/l)

20 Discussions(1) The RICEWQ and VADOFT model linkage can be applied to predict the pesticide runoff, the dissipation in the paddy water, and the leaching at the bottom of soil column.

21 Discussions(2) Water management, seepage rate and nodal spacing set have a strong influence on the fraction of chemical runoff and leaching. The former is a site-specific property while the latter is a model parameter. However, In the European registration point of view, detailed national scenario definitions are needed to correctly set these inputs.

22 Discussions(3) In a scientific view, several model enhancements are desirable. For examples, water management strategies should be improved to allow the simultaneous simulation of irrigation with drainage. Additional model testing, e.g., volatilization routines, is recommended to fulfill the requirement of a full model evaluation.

23 Working Group Ettore CAPRI 1 Marco TREVISAN 1 Zewei MIAO 1 W. Martin Williams 2, J. Mark Cheplick 2 1 Istituto di Chimica Agraria ed Ambientale, Università Cattolica del Sacro Cuore - Piacenza - Italy 2 Waterborne Environmental, Inc., 897-B Harrison Street, S. E. Leesburg, VA 20175, USA