Final Report: Pesticide Transport in Subsurface and Surface Water Systems

EPA Grant Number: R825433C052
Subproject: this is subproject number 052 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Pesticide Transport in Subsurface and Surface Water Systems
Investigators: Marino, Miguel
Institution: University of California - Davis
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


Pesticide leaching, runoff, and erosion lead to contamination of both subsurface and surface water systems. The objectives of this research project were to investigate: (1) the fate of nonpoint source pesticides in subsurface and surface environments by developing a systematic procedure and practical analytical tools for evaluating a pesticide residue's potential to leach into groundwater; and (2) the potential threat of pesticide emissions to adjacent rivers/streams.

Summary/Accomplishments (Outputs/Outcomes):

Pesticide fate and transport in the environment primarily are controlled by subsurface and surface settings, hydrologic conditions, and agricultural practices, and are influenced by a set of physical, chemical, and biological processes such as infiltration, runoff, erosion, evapotranspiration, crop-root uptake, advection, dispersion, sorption, decay, and volatilization. We focused our research on characterizing these processes, quantifying the spatial and temporal distributions of pesticide residues, evaluating their potential adverse impacts on water resources, and eventually identifying feasible management practices using modeling techniques.

We developed a series of analytical/numerical and semidiscrete hybrid models for simulating pesticide transport and transformation in the subsurface and surface environments. The models possess various levels of complexity and can be used by different users for distinct research purposes (e.g., screening-level investigations and detailed studies). We also improved the quality and applicability of the models by taking into account various pesticide application methods, developing irrigation simulators, incorporating a variety of modeling methodologies, and facilitating regional-scale simulations. We then applied the integrated models to two sites in California's Central Valley to assess pesticide-induced contamination in surface and groundwaters, and to identify water quality management strategies.

The following activities were accomplished:

• We developed an analytical model for simulating three-phase pesticide transport and transformation in the subsurface environment. The analytical model can be used as a tool for long-term predictions of pesticide leaching potentials and exposure levels in groundwater, as well as screening-level assessment of the vulnerability of the subsurface environment to pesticide contamination. Because this analytical model is relatively simple (when compared to large numerical simulation models) and requires only a small amount of data to quickly obtain pesticide-concentration predictions (as opposed to extensive numerical simulations), it is cost effective in terms of time and input data. A model of this type provides resource managers with a low-cost alternative to expensive and prolonged field monitoring strategies.

• Pesticide runoff and erosion can be significant in many cases. We developed a three-zone analytical pesticide model capable of dealing with these processes. We extended the aforementioned two-zone (crop-root zone and intermediate vadose zone) analytical soil model to a three-zone soil model by adding a thin surface zone, which facilitates the modeling of pesticide runoff and erosion and improves the simulation of volatilization. Our newly developed model will aid in further pesticide contamination research efforts.

• We compared analytical and numerical pesticide transport models to examine their fundamental differences, application conditions, and limitations. A comparison of the developed analytical model with a numerical modeling system that couples PRZM2 and MT3D emphasizes the usefulness of the analytical pesticide transport model, and indicates the limitations of analytical modeling techniques.

• It is often necessary to screen and rank pesticide exposure levels and the extent of the induced contamination. For these purposes, we developed index models for pesticide-related environmental assessment. Index models integrate the effects of the different transport and fate processes into lumped parameters for screening and ranking pesticides. In combination with geographic information system techniques, index models are particularly suitable for regional-scale preliminary assessment of pesticide leaching potentials and groundwater vulnerability to pesticide pollution. They would be useful to resource managers, policymakers, and regulatory agencies.

• We developed improved mass fraction models for multiphase transport and fate of agricultural pollutants in two region-structured or aggregated soils to provide estimates for the likelihood of soil, air, and groundwater contamination. The advantage of these models over mobility index models is that they consider the interaction between the residence time in the soil and different loss and dispersing mechanisms on the likelihood of groundwater pollution by pesticides. The mass fraction models potentially can be used for pesticide management in agriculture and the design and management of organic hazardous waste by land treatment. The groundwater index can be used in delineating protection zones for drinking water wells and streams.

• Different modeling methodologies have distinct numerical properties in terms of accuracy and stability. Substantial numerical errors can be introduced in a transport model, which may lead to further incorrect management decisions. In response, we developed improved pesticide modeling methodologies (i.e., we proposed a hybrid semidiscrete modeling approach). To improve the accuracy and stability of the mathematical solutions and enhance the model applicability, we analyzed analytical and numerical modeling techniques and proposed a hybrid semidiscrete modeling approach for solving pesticide transport problems. We incorporated a set of numerical schemes, including a first-order upwind scheme, second-order central differencing, high-order linear upwind-biased schemes, and a nonlinear van Leer flux limiter, into the integrated modeling system. Other researchers investigating pesticide transport problems may find our approach useful.

• We developed a semidiscrete pesticide transport model for the subsurface environment. Its flexible modeling framework makes the model suitable for either screening-level investigations or detailed studies. Because of its flexible structure, the semidiscrete pesticide transport model can be used as either a lumped, analytical model (if data are scarce and quick decisions are needed) or a distributed, numerical model (if enough data are available for characterizing heterogeneous media, unsteady flow fields, and spatial and temporal variability of complex physical and biochemical processes). The model can be used by regulatory agencies and other researchers for various purposes (preliminary environmental assessment or intensive contaminant transport studies).

• Few pesticide transport models in current use consider the internal linkage of surface and subsurface water systems and the integrity of the hydrosystem. We attempted to fill this gap by developing an integrated pesticide transport model (IPTM) in surface and subsurface environments. The IPTM possesses enhanced capabilities of characterizing the environmental fate of pesticides, quantifying their spatial and temporal distributions, and identifying their pathways throughout the hydrosystem. Internal linkage and joint integration enable the model to characterize the mechanisms and interactions between the subsystems. This enhanced model will allow us to make even more sophisticated predictions about pesticide transport in various environments.

Accomplishments Related to Application Studies

Findings From Application Study 1: Modeling and Assessment of Diazinon Fate and Transport in the Wadsworth Canal Basin, California:

• We found that peak concentrations of diazinon in the surface runoff and canal water correspond to the heavy rainfall events and intensive applications of diazinon during the dormant season. Timing of the rainfall and pesticide application is critical to the environmental fate and transport of diazinon. This information may influence decisions about the timing of pesticide applications to minimize the adverse effects of runoff.

• We determined that diazinon-induced contamination in the subsurface environment is only limited to the shallow soils. Because the contamination is limited to shallow soils, there is little risk of the contamination of underlying aquifers. This information would be useful to farmers, scientists, and regulatory agencies.

Findings From Application Study 2: Modeling and Assessment of Diazinon Fate and Transport in the Orestimba Creek Basin, California:

• This study demonstrated that the magnitude and timing of pesticide application and rainfall/irrigation dominate exposure levels of diazinon residues in both subsurface and surface environments. High concentrations of diazinon at Orestimba Creek are determined by the availability of both surface runoff water and applied diazinon.

• We determined that irrigation methods play an important role in the environmental fate and transport of pesticides. Thus, integrated water-pesticide-crop management can be an effective way to minimize pesticide contamination in surface and subsurface environments.

• Our modeling efforts show that no obvious threat to the groundwater system can be inferred because of the low permeability of soils and the large thickness of the vadose zone. This information may inform water quality regulation agencies in future decisionmaking.

• Diazinon exposure levels in the creek may exceed the water quality standards for both aquatic life and human health, and high-peak pulses of diazinon may last about one-half a month. These results could influence decisions regarding water quality standards in areas of diazinon exposure.

Supplemental Keywords:

ecosystem, ecosystem protection, environmental exposure and risk, geographic area, international cooperation, water, terrestrial ecosystems, aquatic ecosystem, aquatic ecosystem restoration, aquatic ecosystems and estuarine research, biochemistry, ecological effects, ecological indicators, ecological monitoring, ecology and ecosystems, environmental chemistry, restoration, state, water and watershed, watershed, watershed development, watershed land use, watershed management, watershed modeling, watershed restoration, watershed sustainability, agricultural watershed, exploratory research environmental biology, California, CA, Clear Lake, Lake Tahoe, anthropogenic effects, aquatic habitat, biogeochemical cycling, ecological assessment, ecology assessment models, ecosystem monitoring, ecosystem response, ecosystem stress, environmental stress, environmental stress indicators, fish habitat, hydrologic modeling, hydrology, integrated watershed model, lake ecosystems, lakes, land use, nutrient dynamics, nutrient flux, water management options, water quality, wetlands., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Aquatic Ecosystem, Fate & Transport, Monitoring/Modeling, Environmental Microbiology, Biochemistry, Terrestrial Ecosystems, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Watersheds, aquatic, fate and transport, ambient particle properties, ecosystem assessment, watershed management, Sacramento River, pesticides, sediment transport, modeling, restoration strategies, hydrology, watershed influences, chemical kinetics, integrated watershed model, wetland restoration, aquatic ecosystems, environmental stress, groundwater contamination, watershed sustainablility, source load modeling, material transport, ecology assessment models, vadose zone, ecological impact, agrochemicals, ecosystem stress, ecological research, watershed restoration

Relevant Websites: Exit

Progress and Final Reports:

Original Abstract
  • 1997
  • 1998
  • 1999 Progress Report

  • Main Center Abstract and Reports:

    R825433    EERC - Center for Ecological Health Research (Cal Davis)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
    R825433C002 Sacramento River Watershed
    R825433C003 Endocrine Disruption in Fish and Birds
    R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
    R825433C005 Fish Developmental Toxicity/Recruitment
    R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
    R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
    R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
    R825433C009 Modeling Ecosystems Under Combined Stress
    R825433C010 Mercury Uptake by Fish
    R825433C011 Clear Lake Watershed
    R825433C012 The Role of Fishes as Transporters of Mercury
    R825433C013 Wetlands Restoration
    R825433C014 Wildlife Bioaccumulation and Effects
    R825433C015 Microbiology of Mercury Methylation in Sediments
    R825433C016 Hg and Fe Biogeochemistry
    R825433C017 Water Motions and Material Transport
    R825433C018 Economic Impacts of Multiple Stresses
    R825433C019 The History of Anthropogenic Effects
    R825433C020 Wetland Restoration
    R825433C021 Sierra Nevada Watershed Project
    R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
    R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
    R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
    R825433C025 Regional Movement of Toxics
    R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
    R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
    R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
    R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
    R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
    R825433C031 Pre-contact Forest Structure
    R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
    R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
    R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
    R825433C035 Border Rivers Watershed
    R825433C036 Toxicity Studies
    R825433C037 Watershed Assessment
    R825433C038 Microbiological Processes in Sediments
    R825433C039 Analytical and Biomarkers Core
    R825433C040 Organic Analysis
    R825433C041 Inorganic Analysis
    R825433C042 Immunoassay and Serum Markers
    R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
    R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
    R825433C045 Microbial Community Assays
    R825433C046 Cumulative and Integrative Biochemical Indicators
    R825433C047 Mercury and Iron Biogeochemistry
    R825433C048 Transport and Fate Core
    R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
    R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
    R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
    R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
    R825433C053 Currents in Clear Lake
    R825433C054 Data Integration and Decision Support Core
    R825433C055 Spatial Patterns and Biodiversity
    R825433C056 Modeling Transport in Aquatic Systems
    R825433C057 Spatial and Temporal Trends in Water Quality
    R825433C058 Time Series Analysis and Modeling Ecological Risk
    R825433C059 WWW/Outreach
    R825433C060 Economic Effects of Multiple Stresses
    R825433C061 Effects of Nutrients on Algal Growth
    R825433C062 Nutrient Loading
    R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
    R825433C064 Chlorinated Hydrocarbons
    R825433C065 Sierra Ozone Studies
    R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
    R825433C067 Terrestrial - Agriculture
    R825433C069 Molecular Epidemiology Core
    R825433C070 Serum Markers of Environmental Stress
    R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
    R825433C072 Molecular Monitoring of Microbial Populations
    R825433C073 Aquatic - Rivers and Estuaries
    R825433C074 Border Rivers - Toxicity Studies