Factors Impacting Fish Communities

A composite of 2 photos showing the same area of a stream in Great Smoky Mountains National Park. One photo was taken during a drought year (left) and the other photo during a flood year (right).
A composite of two photos showing the same area of stream within Great Smoky Mountains National Park.  The first photograph shows the stream during a drought year (left).  The second photograph shows the same area of that stream during a flood year (right).

National Park Service Photo


You’re Right!

Major droughts reduce the adult numbers of fish and major floods limit reproductive success. Droughts reduce fish numbers by drying up portions of the stream, further, reducing an already limited food supply.

The park receives the highest sulfur and nitrogen deposits of any monitored national park. These pollutants fall to the ground not only as acid rain, but also as dry particles and cloud water. The average acidity (pH) of rainfall in the park is 4.5. That is 5-10 times more acidic than normal rainfall which is 5.0-5.6. Acidic clouds with a pH as low as 2.0 bathe the high elevation forests during part of the growing season.

Great Smoky Mountains National Park has more tree species than Northern Europe. Forest types can influence the water temperature, turbidity, and available cover within park streams.

Fisheries staff have been monitoring fish populations in both high elevation (>3,000 feet) brook trout streams and low elevation (<2,500 feet) large stream systems through the park since 1986. Long term monitoring surveys indicate that fishermen play little to no role in the population dynamics observed in park streams.

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Last updated: April 14, 2015

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