| Abstract: | This dissertation consists of work conducted on the atmospheric transport of pesticides from California's Central Valley to the Sierra Nevada mountains. During the winter of 1995–1996 single event wet deposition samples were collected at 533-m and 1,920-m elevations in the Sequoia National Park, located on the southwestern slope of the Sierra Nevada mountain range. Samples acquired at these locations contained chlorothalonil (0.57–85 ng/L), and chlorpyrifos, diazinon, and malathion ranging from 0.045–24 ng/L. Similar concentrations of chlorothalonil and chlorpyrifos were found in snow and surface water samples collected at Lake Tahoe in the central Sierra Nevada, during this time. Transport of pesticides during the summer months to the Sequoia National Park was assessed by collecting air, dry deposition and surface water samples in 1996. Pesticides found in highest concentrations matched peak summer applications of chlorpyrifos and endosulfan. Air concentrations ranged from 30 ng/m 3 at the 200-m elevation to below the limit of quantitation (0.5 pg/m 3) at the 1,920-m elevation. Surface water samples contained the same profile of pesticides as found in summer air. Detectable concentrations ranged from 0.4 ng/L to 122 ng/L. Surface water and frog tadpoles (Hyla regilla) were collected in 1998 in a transect of northern California from the Pacific Coast to Lake Tahoe. This study ascertained whether the agricultural communities of the Sacramento Valley were a significant source of pesticide residues to the northern Sierra Nevada mountain range. Detectable levels of diazinon were found in the surface waters in Sacramento Valley; no detectable pesticides were found past the foothills of the Sierras. While the data presented in this dissertation are not sufficient to make a complete evaluation of pesticide impact to the Sierra Nevada mountain range, conclusions can be made. Most pesticide concentrations show a clear correspondence between time and intensity of application rather than total annual usage. Pesticides in air, wet deposition and surface water are consistently higher at lower elevations, diminishing in higher elevations due to dilution and degradation during transport. Pesticide concentrations are below acute toxicity values for aquatic species. If pesticides are having an impact we were unable to determine an effect. Note: dissertation citations and abstracts contained here are published with permission of ProQuest Information and Learning. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by addressing your request to UMI® Dissertation Services, 300 North Zeeb Road, Ann Arbor, MI 48106-1346 USA. Telephone (734) 761-7400; Web-page: wwwlib.umi.com/dissertations. |
