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U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigations Report 99-4018B

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Do Herbicides Impair Phytoplankton Primary Production in the Sacramento-San Joaquin River Delta?

By Jody L. Edmunds, Kathy M. Kuivila, Brian E. Cole, and James E. Cloern

This paper is available in pdf format: pdf Edmunds.pdf


The effect of herbicide concentration on the maximum rate of phytoplankton primary production (Pmax) was examined for 53 water samples collected at 9 sites in the Sacramento-San Joaquin River Delta between May and November, 1997. Samples were analyzed for Pmax and the concentrations of diuron, atrazine, cyanazine, simazine, thiobencarb, and hexazinone. The herbicide concentrations ranged between 0 µg/L and 2.1 µg/L, with 50% of the values (n=318) between 0 and 0.018 µg/L. Herbicide concentrations in 52 of the water samples were well below the lowest observable effect concentrations (LOECs) that have been reported in laboratory experiments to inhibit primary production. Pmax ranged between 2 and 11 milligrams of carbon per milligrams of chlorophyll a per hour (mg C (mg chla-h))-1 for the 52 samples where the herbicide concentrations were less than any reported LOEC. However, for the one sample where the diuron concentration (2.1 µg/L) exceeded the reported LOEC of 2.0 µg/L, Pmax was the lowest observed during the study, 0.9 mg C (mg chla-h)-1. Herbicide concentrations we observed throughout the system do not appear to limit production; however, localized occurrences of elevated herbicide concentrations exist and may affect primary production.

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