Can streams containing Apache Trout be cooled? Relationships between environmental variables and stream temperature with management implications under climate change

Authors: Joy Price, Scott A. Bonar

Year: 2012 (xliv)

Abstract

The distribution of Apache trout, Oncorhynchus gilae apache, a threatened species endemic to eastern Arizona, and that of other Southwestern coldwater species, may be compressed due to increased stream temperatures, potentially further exasperated by global climate change. Knowledge of environmental conditions which best buffer stream temperatures against temperature increase and fluctuation may help preserve current Apache trout distribution. We measured relationships of various environmental variables to water temperature in four Arizona streams, and modeled how management activities could be used to cool streams to temperatures below the upper thermal tolerance of Apache trout. Changes in stream discharge; density and species of riparian vegetation; and channel width were evaluated. Altering stream discharge had the greatest effect on stream temperature. Increasing stream discharge an average of.0728 cms cooled streams 1 C. Narrowing the stream channel had a greater cooling effect on wider streams with a higher level of discharge. The percent decrease in channel width required to lower streams 1 C ranged from 14% to 52% depending on the level of discharge. Increasing riparian vegetation density also kept stream temperatures from reaching critical levels; an average increase in total shade of 7% resulted in a 1 C decrease in maximum stream temperature. Ponderosa pine, Pinus ponderosa, provided the greatest level of shade, followed in decreasing order by, Douglas fir, Pseudotsuga menziesii, engelmann spruce, Picea engelmannii, bebb willow, Salix bebbiana, Arizona alder, Alnus oblongifolia, and coyote willow, Salix exigua. Many complex and variable parameters affect stream temperature, but biologists may cost effectively alter these parameters to lower the stream temperatures of many systems below critical thresholds for Apache trout or other coldwater species.