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DISTRIBUTIONS OF AIRBORNE AGRICULTURAL CONTAMINANTS RELATIVE TO AMPHIBIAN POPULATIONS IN THE SOUTHERN SIERRA NEVADA, CA
Citation:
Bradford, D F., E M. Heithmar, C L. Cross, B. Gentry, G M. Momplaisir, M S. Nash, N G. TallentHalsell, L A. Riddick, C G. Rosal, AND K E. Varner. DISTRIBUTIONS OF AIRBORNE AGRICULTURAL CONTAMINANTS RELATIVE TO AMPHIBIAN POPULATIONS IN THE SOUTHERN SIERRA NEVADA, CA. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-01/085 (NTIS PB2002-102156), 2001.
Impact/Purpose:
The overall goals of the task are to apply NERL's core capability in advanced chemical science and technology for maximum benefit in estimating exposures of ecosystems and humans to chemical stressors and to identify emerging pollution concerns, in particular long-range airborne transport of contaminants. This task comprises several subtasks, each with individual objectives:
Subtask 1: screen exposures of National Park PRIMENet ecosystems to chemical stressors, identifying indications of exposure requiring further evaluation, and use these samples evaluate new analytical methods as replacements for standard methods in future assessments of ecosystem contaminant exposures.
Subtask 2: evaluate a new mercury analytical approach with superior performance on complex solid matrices such as biological tissues, and apply the approach to estimating exposure of ecosystems and humans to mercury.
Subtask 3: determine distribution patterns of chemical contaminants in the southern Sierra Nevada Range of California, investigate topographic and weather factors that may influence the distributions, and determine if a correlation exists between contaminant distributions and extirpation patterns of the mountain yellow-legged frog.
Subtask 4: provide analytical methods to measure a number of inorganic and organic arsenic species in a variety of environmental matrices, elucidate the environmental transformations undergone by organoarsenic animal-feed additives, and determine if the potential exists for substantially increased exposure of humans and aquatic organisms to arsenic.
Description:
The Sierra Nevada mountain range lies adjacent to one of the heaviest pesticide use areas in the USA, the Central Valley of California. Because of this proximity, concern has arisen that agricultural pesticides, in addition to other contaminants, are adversely affecting the natural resources of the Sierra Nevada. Transport and deposition of pesticides from the Central Valley to the Sierra Nevada has been documented, and several lines of evidence have implicated pesticide drift from the Central Valley as a causal factor in the dramatic population declines of four amphibian species in the Sierra Nevada.
This study focuses on contaminants in lakes at high elevation in the southern Sierra, an area where unexplained population declines of one species, the mountain yellow-legged frog, have been dramatic. The southern Sierra is of particular interest because air pollution in the Central Valley and Sierra is generally greatest in the south, watersheds in the southern Sierra differ substantially in their proximity to the Central Valley, and the region includes large areas where the mountain yellow-legged frog has completely disappeared and other areas where large numbers remain.
The goals of this study are to: (1) describe the temporal and spatial patterns of distribution of more than 30 chemical contaminants, especially agricultural pesticides (i.e., insecticides and herbicides), all of which are expected to occur in very low concentrations; (2) identify the topographic and spatial attributes of the landscape that influence contaminant distributions (e.g., upslope air flowpath distance from the Central Valley, and elevation); and (3) determine whether there is an association between contaminant distributions and unexplained population extinctions of the mountain yellow-legged frog. We will conduct a study of temporal variation of contaminant concentrations in six lakes in three major watersheds from approximately late summer of 2001 through autumn of 2002. Media sampled will be the snow pack, lake water, sediment, semi-permeable membrane devices suspended in lake water, and possibly dry deposition from the atmosphere. In 2002 or 2003 we will conduct a spatial survey of contaminants in at least 60 lakes in four major watersheds over a 130-km segment of the southern Sierra. We will also collect tadpoles of the ubiquitous Pacific treefrog for
determination of acetylcholinesterase activity. Suppression of activity of this neurological transmitter hydrolase has been used as an indicator of exposure to pesticides. Results of the spatial survey of contaminants will be used in an analysis of the current and former distributions of the mountain yellow-legged frog and Pacific treefrog based on results of ongoing biological surveys for amphibians, fish, and habitat characteristics in 3200 water bodies in Sequoia and Kings Canyon National Parks. We will also analyze lake water and other media for contaminants no longer used in the Central Valley. Some of these may be transported from other continents, and some may be selectively deposited at the higher elevations.