Water Temperature

Summary

Water temperatures support native aquatic life.

General Information
What is it?

Surface water temperature is a constant variable of any water-body and can be measured and summarized in various ways. Maximum seven day average daily maximum (7DADM) was calculated for each year and for each sub-watershed. Each year was represented by the highest seven-day average maximum water temperature within the year.

Why is it important?

One of the consequences of increased withdrawal of river water for human uses is an increase in water temperature due to lowered volume. Increase of river temperatures from their natural levels has far-reaching effects on local ecology, including alteration of community processes and facilitating invasion by exotic species (Poole & Berman 2001). Restoring natural flow regimes and thus natural temperatures is critical to restoring a healthy natural system. Native salmonid species are of great ecological, economic, and cultural importance to local communities. They also serve as strong indicators of habitat quality and integrity in river systems, particularly with regard to water temperature, sediment load, and barriers to passage. They are well-studied, including behavioral and physiological responses to temperature extremes. The Central Valley spring run of Chinook salmon is listed as a threatened species under the ESA, giving them a high priority for restoration. The main threats to the remaining populations are loss and degradation of habitat. In particular, rising water temperature combined with upstream dams has greatly diminished available juvenile summer habitat. Maximum water temperature is a critical part of habitat quality for salmonids. Temperature affects every aspect of salmonid biology, from feeding and growth rates to migration and spawning, and stress levels and survival (Carter 2005). Rainbow trout, for example, are more severely impacted by temperatures in excess of 20°C than by fishing pressure (Runge & Peterson 2008). Upstream diversion of water for human usage increases downstream temperatures, as the lower remaining volume warms more quickly. Due to upstream barriers such as dams, only less-suitable, high-temperature regions are available for spawning and summer feeding. Anthropogenic temperature increases have been identified as key contributors to salmon decline (US EPA 2003).

What can Influence or Stress Condition?

Major factors which raise water temperature are decreased flow within the river, return flows (e.g., from irrigation, water treatment), lack of shading, and increasing air temperatures. Low water volume allows the sun to warm the river much faster, and temperatures increase rapidly as the water moves downstream. Prolonged decreased flow (as opposed to seasonal variations) is most often due to human water use; water is retained in reservoirs and diverted to urban centers or for agricultural use, and only a small fraction is released into the original channel. Increasing temperature due to climate change is likely to be in an increasingly important factor.

Target or Desired Condition

US EPA suggests as a guideline that a river sustaining salmonid populations should not have 7DADM temperatures over 18°C to avoid impairment of salmon health. Similarly, migratory portions of the river should not exceed Maximum Weekly Maximum Temperatures of 20°C and temperatures greater than 22°C will cause broad mortality (US EPA 2003). For core rearing areas in mid-to-upper parts of the river basin, a maximum of 16°C may be appropriate. Experimental studies indicate that spawning temperatures up to 16.5°C do not have deleterious effects on juvenile salmon, but mortality increases markedly after that point (Geist et al. 2006). These temperature guidelines, along with additional information from Brett et al. (1982), were used to convert monthly maximum 7DADM into a 0-100 scale. A score of 100 is equivalent to the EPA’s stated protective criteria of 18°C 7DADM for secondary foraging/rearing areas. A score of 0 will be equivalent to an instantaneous 7DADM temperature of 25°C, the lethal point for juvenile Chinook salmon. Intermediate scores were scaled using an adaptation of the Brett et al. (1982) growth curve (Figure 1). Only the right side of the curve was used; temperatures below the EPA protective criterion were still scored as 100. Brett et al. (1982) estimate that natural populations of Chinook feed at roughly 60% of saturation (or R=0.6, the lowest growth curve). Because of daily temperature fluctuation, 7DADM temperatures are equivalent to constant laboratory temperatures roughly 1-2°C colder (US EPA 2003). The scaling curve is shown in Figure 2. The scaling curve does not exactly match the growth curve, due to the temperature thresholds for 0 (25°C) and 100 (18°C). Temperatures for the growth curve were adjusted upward by 1.5°C to adjust for the use of 7DADM measurements. These scores are most applicable to summer maximum temperatures.

References

Brett JR, Clarke WC, Shelbourn JE. 1982. "Experiments on thermal requirements for growth and food conversion efficiency of juvenile chinook salmon, Oncorhynchus tshawytscha." Can Tech Rep Fish Aquat Sci 1127. 29 p.

Carter, K. 2005. "The effects of temperature on Steelhead trout, Coho salmon, and Chinook salmon biology and function by life stage." California Regional Water Quality Control Board

Geist, D.R., C.S. Abernethy, and K.D. Hand. 2006. "Survival, development, and growth of fall Chinook salmon embryos, alevins, and fry exposed to variable thermal and dissolved oxygen regimes." Transactions of the American Fisheries Society 135:1462-1477.

Poole, G.C. and C.H. Berman. 2001. "An ecological perspective on in-stream temperature: natural heat dynamics and mechanisms of human-caused thermal degradation." Environmental Management 27:787-802.

Runge, J.P. and J.T. Peterson. 2008. "Survival and dispersal of hatchery-raised rainbow trout in a river basin undergoing urbanization." North American Journal of Fisheries Management 28:745-767.

U.S. Environmental Protection Agency (USEPA). 2003. "EPA Region 10 Guidance for Pacific Northwest State and Tribal Water Quality Standards." Region 10, Seattle, WA. EPA 910- B-03-002. 49pp. Available online at: http://www.epa.gov/r10earth/temperature.htm.

U.S. Environmental Protection Agency (USEPA). 2001. "Issue Paper 5: Summary of Technical Literature Examining the Physiological Effects of Temperature on Salmonids." Region 10, Seattle, WA. EPA 910-D-01-005. 119pp.