Pesticide pollution has been a pervasive concern across the world in recent years. Pesticide loss has been regarded as a major nonpoint source (NPS) pollution problem since pesticide usually features toxicity, carcinogenicity and persistence. Effective management is needed to mitigate its environmental impacts, which should be based on a variety of simulation and assessment studies. However, there has been a lack of comprehensive modeling research in simulation and assessment of pesticide pollution. Consequently, to facilitate more effective pesticide-pollution mitigation, advanced simulation and assessment studies are desired.

In this dissertation research, an integrated modeling system has been developed to support pesticide pollution control. The system contains elements of pesticide transport simulation, distributed modeling, risk assessment, and geomatic analysis. In detail, they include:​ (a) a GIS-based distributed pesticide loss model (PeLM) for simulating pesticide loss through surface runoff and soil erosion;​ (b) a pesticide canopy emission module (PeCM) for simulating pesticide volatilization to the atmosphere from plant canopy;​ (c) a pesticide subsurface leaching module (PeSM) for simulating pesticide transport in soil;​ (d) a pesticide movement modeling system (PeMM) for comprehensively predicting pesticide loss to air, water and soil based on an integration of the PeLM, PeCM and PeSM;​ (e) a pesticide-loss simulation and health-risk assessment (PSHA) system for predicting pesticide pollution and evaluating the associated health impacts;​ (f) an integrated modeling system for examining the relationship between climate change and pesticide pollution.

The major contribution of this research is the advancement of a set of simulation and assessment methodologies with regards to the NPS pollution, particularly for the development of the PeMM. The PeMM is the first mathematical modeling system capable of simulating pathways of pesticide transport. Through this system, dynamics of pesticide movement, spatial variability of pesticide distribution, multi-pathways of pesticide transport, and complexity of weather-water-soil interactions can be effectively reflected. The simulation-based budget analysis of pesticide loss and risk assessment of pesticide pollution, which cannot be found in the literature, can also be performed. The developed methodologies have been applied to real-world cases in the Lake Erie Basin, demonstrating satisfactory results. Furthermore, based on the simulation models, the PSHA system is established to predict pesticide loss through flooding water and to evaluate the associated health-impact risks. This research also contains the first attempt to quantitatively examine the relationships between climate change and pesticide pollution, through development of a simulation-based modeling system. Generally, this dissertation research provides useful means for examining and forecasting the fate and transport of pesticides in watershed systems. The research outputs will be useful for supporting pesticide-pollution control.