The Impacts of Copper use in Lily Bulb Cultivation on Juvenile Coho Salmon in the Smith River

Plain

Prof. Matthew Hurst

Department of Chemistry, Cal Poly Humboldt

September 30th, 2022 2:00 – 2:50PM (Sci A 564)

ABSTRACT

The Smith River in California is designated as a wild and scenic river and is one of the most pristine rivers in the United States outside of Alaska. The exception to these pristine conditions is where the river corridor dissects the agricultural fields in the Smith River Plain, and 95% of the world’s Easter Lilies are grown. The use of copper as a fungicide is a concern in the region, which is an important habitat for fry, juvenile, and smolt Coho salmon, a federally protected species. Previous laboratory studies have shown that acute copper toxicity in juvenile salmonids can occur at extremely low copper concentrations (0.2 µg/L), causing a loss in olfactory sensory function and inducing predatory avoidance behavior. This study used spectrometric and electrochemical methods to determine the physical and chemical speciation of copper in stream tributaries at locations above and below the agricultural fields in the Smith River Plain. The copper bioavailability in the Smith River Plain samples was measured and compared to results from previous laboratory studies where dissolved copper (dCu) toxicity thresholds for juvenile Coho salmon were determined. The results from this study show the importance of dissolved organic carbon (DOC) in suppressing the concentration of the bioavailable copper (Cu2+) and promoting an excess of strong organic ligands that buffer the system when high levels of copper enter the waterways. The talk will also dive into the next phase of this research and describe how land management practices may potentially be used to reduce agricultural erosion and the transport of copper to the stream tributaries.