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
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:
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.