The American River is considered to be a high-quality water source for the Sacramento metropolitan area. Previous studies of the lower American River reported that pyrethroid insecticides were detected in grab water samples collected over a 30-km reach of the lower American River at concentrations reported to be toxic to the amphipod Hyalella azteca. Beginning in 2011 we performed an innovative, multi-year monitoring study with the goal of providing a robust understanding of how pyrethroid concentrations vary spatially and temporally in the lower American River. Water samples were collected during 11 rain events and 3 dry events along multiple cross-river transects. The sampling design initially included sample collection at multiple depths, and later transitioned to depth-integrated samples. In addition, water samples were collected from select events for toxicity testing with H. azteca. In summary, pyrethroid concentrations have been found to be episodic, generally low and highly spatially variable, indicating that caution should be used when drawing general ecological conclusions based on grab sampling from the bank.

Multi-year temporal and spatial evaluation of pyrethroid concentrations and biological effects in the lower American River

248th National Meeting (2014)

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