WP4 Pesticides in Pacific Northwest (USA) Watersheds
204 Oregon Ballroom
1:20 PM - 4:40 PM, Wednesday

() Watershed-based Ecological Risk Assessment of Pesticide Use in Western Oregon: A Model-based Approach.

Vache, Kellie1, Bolte, John1, Jenkins, Jeffrey1, Jepson, Paul1, 1 Oregon State University, Corvallis, OR, USA

ABSTRACT- Since the mid-1990s, with the listing of certain Pacific Northwest salmon species as threatened under the Endangered Species Act, there has been an increased interest in watershed health in the Pacific Northwestern United States. One result of these listings has been an emphasis by regional regulatory and planning agencies on the development of tools for examining, at a watershed scale, a range of potential stressors on aquatic populations. Pesticides are one class of stressor that has received attention because of their widespread use and potential to impact a variety of aquatic and riparian ecosystems. Because many watersheds in the Pacific Northwest include a variety of land uses (i.e., urban, rights-of-way, rangeland, forestry, and agricultural uses), stream health impacts of pesticide use should be evaluated considering the chemical use practices associated with these land uses. To address the spatially- and temporally-distributed nature of pesticide application, fate, and transport in multi-use watersheds, two existing models where coupled to produce a new model describing pesticide dynamics at a watershed scale. The first model, WET-Hydro, is a watershed-level, spatially-distributed hydrologic model describing surface and subsurface hydrological processes and taking into account watershed land use and soil property distribution patterns. The second model, PRZM3, is a widely used, 1-dimensional, and highly-parameterized evaluation of the fate and transport of a wide variety of chemicals. The resulting model, WET-Pest, was designed to utilize readily available GIS datasets, incorporate widely-accepted process descriptions for pesticide fate and transport, consider the spatial configuration of chemical applications, vegetative patterns, and topography of a watershed, and produce outputs that allow accounting of pesticides through time and space.

Key words: models, watersheds, PRZM, GIS

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