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Central Columbia Plateau - Yakima River Basin

Scientific Topics - Agricultural Chemical Transport Study

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The Agricultural Chemical Team (ACT) study will focus on the sources, transport and fate of agricultural chemicals. This topical team will address the overall question:

"How do natural processes and agricultural practices interact to affect the transport and fate of agricultural chemicals in the hydrologic system of nationally important agricultural settings, and what are the effects on water quality and implications for management of water resources?"

Nutrients, pesticides, and pesticide metabolites (breakdown products of pesticides) will be included. The studies will be conducted in five NAWQA Study Units across the country including the CCYK during 2001-2004.

This study will take a comprehensive approach to the hydrologic environment and will cover a range of components that are important to the movement and breakdown of agricultural chemicals. The environmental compartments that will be included are atmosphere, unsaturated soil zone, ground water, surface and subsurface drainage, surface water, and the interactions between surface water and ground water in the near-stream environment.

In addressing the overall question, the goal is to achieve specific objectives for several nationally important agricultural settings. Each agricultural setting is a unique combination of an agricultural system and a hydrologic setting. An agricultural system is defined as a regionally extensive combination of specific crop and animal production activities (such as orchards, pastures, row crops and livestock) and associated management practices (such as pesticide use, irrigation, drainage, and tillage). A hydrologic setting is a combination of surface and subsurface hydrologic systems with characteristic climate, topography, geology, and soils. The objectives for each agricultural setting selected for study are:

  1. Develop an annual, mass budget for water and selected agricultural chemicals in the important hydrologic compartments of the agricultural setting.
  2. Determine the residence times and rates of water and agricultural chemical transport among the hydrologic compartments as affected by natural factors and agricultural practices.
  3. Identify the important chemical transformation and transfer processes for selected agricultural chemicals in and between each of the hydrologic compartments and as affected by natural factors and agricultural practices.
  4. Use quantitative methods for the interpretation, extrapolation, and prediction of the fate and transport of water and selected agricultural chemicals, which can be applied to similar agricultural settings at a range of scales.
  5. Interpret study results as to the implications for managing the water and water-quality impacts of agricultural systems.

To address these objectives, the CCYK study unit will select an indicator watershed within the Yakima River Basin that represents a nationally important agricultural setting. Data collection will occur at three nested scales of study ranging from the small watershed scale (one to tens of square miles) up to NAWQA integrator-watershed scale (tens of thousands of square miles). The multiple scales are necessary to understand how the natural hydrologic setting and the superimposed agricultural system interact to affect the fate of agricultural chemicals in the watersheds. By contrasting and comparing results from a variety of scales and a variety of settings, the study will (1) assess the influence of differing agricultural practices on water quality and the ecosystem, and (2) assess the degree to which methods and results from this work can be successfully be transferred to larger scales or to different settings.

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