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Temporal Patterns of Airborne Pesticides in Alpine Lakes of the Sierra Nevada, California
Citation:
BRADFORD, D. F., E. M. HEITHMAR, N. G. TALLENT-HALSELL, G. MOMPLAISIR, C. G. ROSAL, K. E. VARNER, L. A. RIDDICK, AND M. S. NASH. Temporal Patterns of Airborne Pesticides in Alpine Lakes of the Sierra Nevada, California. Presented at Society for Environmental Toxicology and Chemistry, Tampa, FL, November 16 - 20, 2008.
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Presentation
Description:
Airborne agricultural pesticides are being transported many tens of kilometers to remote mountain areas, and have been implicated as a causal agent for recent, dramatic population declines of several amphibian species in such locations. Largely unmeasured, however, are the magnitude and temporal variation of pesticide concentrations in these areas, and the relationship between pesticide application and pesticide appearance in the environment. We addressed these topics in the alpine habitat of the mountain yellow-legged frog complex (Rana muscosa complex) by sampling water from four lakes at high elevation (3042-3645 m) in the southern Sierra Nevada, California, from mid June to mid October, 2003. The lakes ranged between 46 and 83 km from the nearest pesticide sources in the intensively cultivated San Joaquin Valley. Eight of 40 target pesticide analytes were detected at least once among the four lakes, and four occurred at frequencies that allowed us to evaluate temporal patterns: endosulfan, propargite, dacthal, and simazine. Concentrations at all times were extremely low, generally less than 1 ng/L for the first three, and only slightly higher for simazine. For endosulfan and propargite, temporal variation in concentrations corresponded with application rates in the San Joaquin Valley, with a lag time of 1 and 2 weeks, respectively. A finer-scale analysis suggests that a disproportionate fraction of the pesticides reaching the lakes originated within nearby upwind portions of the San Joaquin Valley. Temporal patterns in pesticide concentrations were generally consistent among the four lakes. Mountain yellow-legged frog populations have largely disappeared from the vicinities of lakes with both the high and low pesticide concentrations observed in the study.