An Investigation into the Impacts of Copper use in Lily Bulb Cultivation on Juvenile Coho Salmon in the Smith River Plain using Speciation and Physico-Chemical Methods

The Smith River in California is designated as a wild and scenic river and is one of the mostpristine rivers in the United States outside of Alaska. The exception to these pristineconditions is where the river corridor dissects the agricultural fields in the Smith RiverPlain, where 95% of the world's Easter Lilies are grown. The use of copper as a fungicide isof concern in the region, which is an important habitat for fry, juvenile, and smolt Cohosalmon, a federally protected species. Previous laboratory studies have shown that acutecopper toxicity in juvenile salmonids can occur at extremely low copper concentrations,causing a loss in olfactory sensory function and inducing predatory avoidance behavior.This study used spectrometric and electrochemical methods to determine the physical andchemical speciation of copper in stream tributaries at locations above and below theagricultural fields in the Smith River Plain. The copper bioavailability in the Smith RiverPlain samples was determined by comparing the [Cu 2+ ] in water samples to previous worksin the laboratory that determined the dissolved copper (dCu) toxicity thresholds thatinduce a toxic response in juvenile Coho salmon. The [Cu 2+ ] in the replicated laboratorysolution at the copper toxicity threshold was found to be 190 +/- 30 pg/L. All of the SmithRiver Plain samples contained excess strong ligands and levels of Cu 2+ that were an order ofmagnitude below this threshold for copper toxicity. The results showed that thebioavailable copper (Cu 2+ ) was dictated by dissolved organic carbon (DOC) concentrationsin both wet and dry seasons. Water conditions that created a vulnerability for juvenileCoho salmon were at [DOC] < 0.5 mg/L and low hardness. The study found that dCu levelswere higher downstream of agricultural fields when compared to upstream measurements.Using dCu as a variable to predict potential copper toxicity to Coho salmon was not valid.Measurements of high particulate (> 0.2 µm) and colloidal (0.03 -0.2 µm) copper identifiedcatchments where land management practices are needed to reduce agricultural erosionand transport of copper to the stream tributaries.