BRADFORD, D. F., N. G. TALLENT-HALSELL, E. M. HEITHMAR, G. MOMPLAISIR, C. G. ROSAL, M. S. NASH, K. E. VARNER, AND L. A. RIDDICK. Temporal and Spatial Patterns of Airborne Contaminants Relative to Amphibian Population in Sequoia and Kings Canyon National Parks, California. Presented at Sierra Nevada - Southern Cascades Contaminants Workshop, Three Rivers, CA, April 08 - 09, 2009.
Airborne agricultural pesticides are being transported many tens of kilometers to remote locations in mountain areas, and they have been implicated as a cause for recent, dramatic population declines of several amphibian species in such areas. The strongest case is for the mountain yellow-legged frog (Rana muscosa), which formerly was nearly ubiquitous among high-elevation waters bodies throughout the Sierra Nevada of California. Evidence for this pesticide effect, however, relies primarily on predicted distributions of pesticides and a few spot measurements. Largely unmeasured are the magnitude and temporal variation of pesticide concentrations in the habitat of this species, the relationship between pesticide application and pesticide appearance in the environment, and associations between the distributions of pesticides and the distribution of population declines. We evaluated temporal variation in pesticide concentrations by sampling water in four widely separated alpine lakes in the southern Sierra Nevada, California, from mid June to mid October, 2003. Four of 40 target pesticide analytes were detected at frequencies that allowed evaluation of temporal patterns: endosulfan, propargite, dacthal, and simazine. Concentrations at all times were extremely low, generally less than 1 ng/L (parts per trillion) for the first three, and only slightly higher for simazine. The temporal patterns in concentrations differed among the four pesticides, whereas the temporal pattern for each pesticide was similar among the four lakes. For the two pesticides applied abundantly in the San Joaquin Valley during the sampling period, endosulfan and propargite, temporal variation in concentrations corresponded significantly with application rates in the Valley with a lag time of 1 and 2 weeks, respectively. We evaluated the pesticide distributions by sampling three media (air, sediment, and tadpoles of the Pacific treefrog, Pseudacris regilla) in 28 water bodies in the Parks twice during the summer of 2005. Nine pesticide compounds were found in sediment and tadpoles, including both historic and current-use pesticides: chlorpyrifos, dacthal, endosulfan I and II, endosulfan sulfate, DDE, chlordane, and nonachlor-cis and -trans. Only endosulfan II was detected frequently in air. Concentrations of all chemicals were low, averaging in the parts-per-billion (ppb) range or less in sediment and tadpoles. A clear pattern of chemical concentrations with distance from the San Joaquin Valley was not apparent. Results do not support the hypothesis that airborne pesticides or other contaminants have contributed to the dramatic population declines of the mountain yellow-legged frog. Virtually no association was found between frog population status and any chemical metric in any of the three media in either sampling period. In contrast, a strong negative relationship was found between frog population status and linear distance from the San Joaquin Valley. This geographic pattern is consistent with the postulated west-to-east movement of the decimating amphibian disease, chytridiomycosis.