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COLD WATER PATCHES IN WARM STREAMS: PHYSICOCHEMICAL CHARACTERISTICS AND THE INFLUENCE OF SHADING
Citation:
Ebersole, J L., W. J. Liss, AND C. A. Frissell. COLD WATER PATCHES IN WARM STREAMS: PHYSICOCHEMICAL CHARACTERISTICS AND THE INFLUENCE OF SHADING. JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION. American Water Resources Association, Middleburg, VA, 39(2):355-368, (2003).
Description:
Discrete coldwater patches within the surface waters of summer-warm streams afford potential thermal refuge for coldwater fishes during periods of heat stress. This analysis focused on reach-scale heterogeneity in water temperatures as influenced by local influx of cooler subsurface waters. Using field thermal probes and recording thermistors, we identified and characterized coldwater patches (at least 3oC colder than ambient streamflow temperatures) potentially serving as thermal refugia for coldwater fishes. Among 37 study sites within alluvial valleys of the Grande Ronde basin in northeastern Oregon, we identified coldwater patches associated with side channels, alcoves, lateral seeps, and floodplain springbrooks. These types differed with regard to within-floodplain position, area, spatial thermal range, substrate, and availability of cover for fish. Experimental shading cooled daily maximum temperatures of surface waters within coldwater patches 2 - 4o C, indicating a strong influence of riparian vegetation on the expression of coldwater patch thermal characteristics. Strong vertical gradients in temperature associated with heating of surface layers of coldwater patches exposed to solar radiation superimposed upon vertical gradients in dissolved oxygen can partially restrict suitable refuge volumes for stream salmonids within coldwater patches.