Pacific Northwest Research Station

Title: Keeping it cool: unraveling the influences on stream temperature.

Author: Thompson, Jonathan.

Date: 2005

Source: Science Findings 73. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p

Description: Water temperature influences virtually every biotic component of stream ecosystems. Not surprisingly, increased summer temperatures in streams with coldwater species of fish such as salmon and trout have become a topic of concern regionally and internationally. Although stream temperature has been studied for many years, controversy continues over the relative influences of shade, air temperature, and substrate on temperature dynamics.

Researchers at the PNW Station have recently conducted experiments and calculated heat budgets that itemize the relative influence of several factors on the water temperature of mountain streams in western Oregon. New technologies allow more detailed measurements of heat fluxes and more accurate determination of the factors affecting stream temperature, allowing management practices to be tailored to minimize their influence on stream ecosystems.

Direct solar radiation is the primary contributor to daily fluctuations in water temperature. Managing for shade by maintaining streamside vegetation is an effective way to reduce heat flux. In addition, the type of substrate and the length of time that stream water spends below the stream channel is an important predictor of daily temperature variations. Much remains to be learned about how these factors vary across the landscape.

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Citation

Thompson, Jonathan.  2005.  Keeping it cool: unraveling the influences on stream temperature..   Science Findings 73. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.