Bibliography: leaves 198-227. / xx, 260 leaves, [3] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The aims of this study were: 1. to examine the sorption behaviour of selected nonionic and ionic pesticides in a range of soils; 2. to characterise the nature of soil organic matter in a diverse group of soils and relate the structural and molecular variations of organic matter to sorption of nonionic pesticides; and 3. to study the release behaviour of carbaryl and ethion from two historically contaminated soils and to elucidate the mechanisms of their aging/sequestration. (abstract) / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 1999

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Prevention of groundwater contamination by agricultural chemicals requires an understanding of the complex processes that control pesticide movement below the soil surface. Through this understanding it is possible to try to predict which areas may be most vulnerable to contamination. The many models that have been developed to characterize pesticide movement vary widely in their conceptual approach and degree of complexity. A soil properties model was developed in this thesis to determine the relative overall pesticide movement potential in Oregon agricultural soils. Its focus is ease of use in both acquisition of input values and running of the model. The model is based on soil properties important in controlling pesticide movement. It is a rating system model that uses scoring of factors and matrices to weigh the soil values. It is organized into two processes: leaching and sorption. The leaching potential is based on soil permeability and drainage class. The sorption potential is based on organic matter content and texture of the soil surface horizon(s). The interaction of these two processes results in the overall pesticide movement potential. / Graduation date: 1991

A three year field study was undertaken to assess the influence of water table management, namely subsurface irrigation and controlled drainage, on the movement of pesticides through the soil profile into ground water. The herbicides under investigation were prometryn on an organic soil, and metolachlor on a sandy soil. Both soil and groundwater were collected and analyzed. The results presented are those obtained in the first two years of the project. / In the organic soil, herbicide leaching was greatly reduced due to the management of the water table. The pesticide remained higher in the soil profile, preventing leaching to the drains and allowing degradation. / The opposite effect appeared to have occurred in the sandy soil. The higher water table resulting from subsurface irrigation may have induced the leaching of the contaminant into lower soil levels and into the ground water. The high water solubility of the herbicide metolachlor, in conjunction with low microbial activity, may have played a role in this phenomenon.

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A field scale model for predicting the surface losses of pesticides (Pesticide Losses In Erosion and Runoff Simulator, PLIERS) was developed. PLIERS accounts for pesticide losses by degradation and volatilization, the washoff of pesticides from plant canopy and surface residue, the adsorption and desorption of pesticides to and from soil particles, and the movement of pesticides in the dissolved and adsorbed phases. Hydrologic data are generated by the comprehensive watershed model, FESHM; which contains an extended sediment detachment and transport algorithm. PLIERS uses first order rate equations to describe degradation and volatilization, and pesticide washoff. The adsorption of pesticides to individual particle size classes is estimated using the Freundlich equation. Movement of atrazine and 2,4-D in runoff and sediment was measured on twelve field plots under simulated rainfall. The plots were treated with conventional or no-tillage in combination with one of three residue levels (0, 750, and 1500 kg/ha). Runoff and sediment losses were found to increase with decreasing residue cover for both tillage systems. No-till reduced sediment loss and total runoff volume by 98 and 92 percent, respectively, compared to conventional tillage. Concentrations of atrazine and 2,4-D ir1 runoff and sediment were greater from the no-till plots than from the conventional plots but the total losses were less. Both pesticides were carried predominately in the dissolved phase. Averaged over all plots, the atrazine losses were 2.9 percent of applied amount for conventional tillage and 0.3 percent for no-tillage. The corresponding values for 2,4-D were 0.3 percent and 0.02 percent. PLIERS was validated using data from the rainfall simulator field plot studies. Agreement between predicted and observed data was very good for dissolved pesticide losses and satisfactory for adsorbed pesticide losses. In addition, the effects of tillage type and residue level were reflected in PLIERS predictions. PLIERS shows great potential as a flexible planning tool since it could be used with any comprehensive hydrologic model and is able to predict the losses of pesticides under various field conditions. / Master of Science

Two different modeling approaches to simulate pesticide fate and transport in soil were investigated in this study. First, a process-based mathematical model, DRAINMOD-P, was developed by combining the attractive features of DRAINMOD and PESTFADE. While DRAINMOD formed the main component to perform hydrological predictions, PESTFADE's pesticide sub-model was used to simulate pesticide fate. The new model was validated against three years of independently collected field data from southern Ontario. Several statistical parameters were calculated to evaluate model performance. / Second, an implicit model, Multivariate Adaptive Regression Splines, MARS, which is also a novel data mining tool, was used to assess pesticide transport. MARS was first validated against the field data on three herbicides, namely, atrazine, metribuzin and metolachlor. DRAINMOD-P and MARS simulations, though impressive, need further validations before they can be recommended for actual real-world use.* / *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office; Adobe Acrobat.

A one-dimensional transient mathematical model which can predict simultaneous movement of water and reactive solutes through homogeneous soil systems under saturated/unsaturated conditions is developed. The physically-based numerical model, called PESTFADE, considers the interactive processes/mechanisms such as mass flow, plant uptake, adsorption/desorption, dispersion, volatilization, chemical/microbial degradation and runoff in the simulation. / The PESTFADE model employs SWACROP, a model developed in the Netherlands, to simulate transient water flow in the unsaturated zone; evaluates non-equilibrium sorption in macropores, analyzes soil heat flow to to model microbial degradation, calculates pesticide partitioning in runoff/sediment as affected by agricultural management practices, and describes first order degradation and sorption kinetics. The governing partial differential equation describing the various processes is solved numerically via the Numerical Method of Lines (NMOL) technique, and the computer programs are written in FORTRAN 77. The resulting computer code (PESTFADE), is run on a microcomputer and has been implemented for interactive simulation on IBM PC or compatible microcomputers. / The model was tested and validated using actual data measured from field plot experiments involving herbicide atrazine which was post-emergently applied in a corn field on a loam soil. Various analytical solutions were used to check the accuracy of the different components of PESTFADE, and parametric sensitivity analyses were performed to determine how the model output reacts to changes in some selected input parameters. / Results indicate that model predictions generally agreed with measured concentrations of atrazine and compared closely with the analytical solutions. Moreover, model performance tests showed that predicted values are within acceptable ranges of model accuracy and bound of experimental uncertainties. It was also found that the model is very sensitive to degradation rate constant (k), sorption coefficient (K$ sb{ rm d})$ and soil temperature and slightly sensitive to management practice (CN) and sorption site fraction (F). Finally, the various field scenarios and pathways for non-point source contamination evaluated in the study have demonstrated the wide applicability and flexibility of PESTFADE.

The work presented in this thesis represents a contribution to the area of modeling of the transport and fate of herbicides applied to cropped fields, and was part of a larger research effort geared towards better management of herbicides. The main objective of this thesis was to develop a graphical user interface (GUI) for PESTFADE, a process-based mathematical model of pesticide transport and degradation, and to provide documentation for the execution of PESTFADE. The model simulates changes in pesticide concentration at different depths in the soil, based on relevant physical, chemical, biological and meteorological factors. PESTFADE is considered to be one of the most comprehensive models of its kind. However, it was, until now, difficult to implement due to absence of a user manual and graphical interface suitable for exploitation in a Windows environment. The author developed the GUI in Visual Basic, created macros to facilitate certain calculations, rewrote the original FORTRAN 77 code and then validated the updated version against field data obtained from an experimental site (Eugene Whelan Farm, Woodslea, Ontario). A preliminary development of an artificial neural network (ANN) to perform the same simulation implicitly, with fewer input parameters and less computational time, was also done. / The thesis describes PESTFADE and the GUI, gives guidelines for implementing the package, and presents the results of the field validation of the revised version. During this work, the author discovered that there were problems in the parts of the code dealing with sorption phenomena. This can be solved by conventional kinetics or by Gamble kinetics.

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