jennifer_gibson@nps.gov
Ecologist, Whiskeytown National Recreation Area, California


Back to Chapter 4: Resource Risks

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By John Wullschleger

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Calling for stronger fossil resource protection: A report to Congress
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By Robert V. Sobczak and Antonio J. Pernas

Change in status of lynx and black-tailed prairie dog

Virus responsible for amphibian deaths in parks

Exotic invertebrates spread

Award-Winner Profile - Maintenance Chief Merry Petrossian recognized with award

Ozone standards exceeded in parks

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Declines in amphibian populations were perhaps one of the most urgent and enigmatic worldwide environmental problems of the late 20th century. Scientists are currently investigating amphibian die-offs in several locations across the United States. Multiple species of frogs, toads, and salamanders and one species of newt are dying off on private, state, and federal lands, including several national parks. Possible causes of the decline include the introduction of nonnative species, increased ultraviolet (UV-B) radiation, acid precipitation, rising global temperatures, pollution, infectious disease, and a combination of factors.

In June 2000, hundreds of dead bullfrog (Rana catesbeiana) tadpoles were found in the lake of Whiskeytown National Recreation Area, California. Although the bullfrogs are a nonnative, invasive species in the recreation area, the dead tadpoles alarmed park staff. Amphibians are sentinels of water quality and environmental degradation because of their different life stages (an aquatic larval stage and a terrestrial adult stage), highly specialized physiological adaptations, and specific microhabitat requirements. Because amphibians have been identified as indicator species for the aquatic and terrestrial ecosystems in Whiskeytown National Recreation Area, several explanations for the die-off were investigated.

Iridoviruses and a newly recognized, yeastlike fungus are the only known infectious diseases that cause large die-offs in tadpoles. A histological examination of the dead tadpoles by the USGS National Wildlife Health Center revealed abnormalities in the gills, skin, and oral disks but no sign of known infectious disease. Thus, what was thought to be an amphibian disease outbreak became a water quality issue.

Whiskeytown Lake lies at the confluence of seven major streams that comprise one of the largest watersheds of the Sacramento River. Land use outside the park boundary was considered a potential source of pollution in the arm of the lake in which the die-off occurred. A bioassessment of the watershed revealed a previously unknown abandoned mine that is associated with the Iron Mountain Mine superfund site, which is well known for having the most acidic waters (pH –3.6) in the world. However, tadpole samples revealed no sign of the heavy metals that are typically associated with acid mine drainage.

The National Park Service now suspects that the most probable cause of the die-off is the introduction of a low-molecular-weight, rapidly metabolized, organic compound. This includes some herbicides and rodenticides, fertilizers, petroleum-based compounds, and several solvents that are associated with the manufacture of illegal substances, such as methamphetamine. Drops of fire retardant, which were numerous in summer 1999, are also suspect because retardants containing sodium ferrocyanide release pure, deadly cyanide when exposed to sunlight. Although the effects of the chemicals associated with retardants are thought to be short-lived, their persistence in the environment is unknown. Pollutants associated with two-stroke engines (MTBE and PAHs) have also been considered, because even at low concentrations, these compounds can harm aquatic organisms through phototoxicity.

The cause of the tadpole die-off in Whiskeytown Lake has yet to be determined. The tissue abnormalities and deaths of the tadpoles emphasize the pressing need for long-term ecological monitoring. Although monitoring in the Klamath Network of the Inventory and Monitoring Program is not funded yet, Whiskeytown National Recreation Area’s future participation in this program may provide critical information about the status of its amphibians and clues to the tadpole die-off.

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Last Updated: 06/17/2001
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