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Publication Date

Spring 2020

Degree Type

Thesis - Campus Access Only

Degree Name

Master of Science (MS)

Department

Environmental Studies

Advisor

Rachel O’Malley

Keywords

Aquatic Organism, GIS, Pesticide, Rice, Risk assessment, Spatial

Subject Areas

Environmental studies

Abstract

Rice is the most important grain in the global agricultural system, currently feeding more than half of the world’s population. Agroecosystems serve as habitat for wildlife, in addition to providing food for humans. Inundated rice fields, or paddies, can be of particular importance to wildlife, as artificial wetlands. Unfortunately, pesticide-contaminated water can be highly toxic to aquatic organisms. In order to assess selected species’ risk of exposure to pesticides in and near rice fields, this work used California’s Pesticide Use Report data for 2016 in the Pesticides in Flooded Applications Model to simulate spatial and temporal concentrations of the fungicide azoxystrobin in the Sacramento area. Model outputs were used to assess the risk to sensitive species and ground-truthed against publicly-available field monitoring data. Model results show that azoxystrobin hotspots were widely distributed across Butte, Colusa, and Glenn counties in July and August 2016. Model concentrations showed acute toxicity risk for copepods (Macrocyclops fuscus) and mysid shrimp (Mysidopsis bahia), with limited toxicity for steelhead/rainbow trout (Oncorhynchus mykiss) and water flea (Daphnia magna). Surface-water monitoring data for azoxystrobin were scarce, but they paralleled model-predicted concentrations across the treated area. Results showed that reducing numbers of applications or dosages of this fungicide would reduce risks to wildlife in the Sacramento Valley.

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