The derivation of water quality guidelines for temperature, based on a single numeric value that provides adequate protection for a designated water use, is extremely challenging given the diversity of aquatic environments in BC that vary with elevation and latitude. Both ecological communities and environmental factors vary widely throughout the province and therefore application of uniform water quality guidelines should not be expected to provide complete protection for all species at all locations. Given the overall size and geography of the province, it is unreasonable to consider that a "one size fits all" approach would adequately address the needs of society or the environment. To this end, a two-tiered approach to guideline development is recommended: 1) province-wide, interim numeric temperature guidelines are suggested to provide generic/conservative protection to designated uses until such time as 2) a surface water use classification is completed at a regional scale. The water use classification approach is recommended to distinguish differences in temperature quality among the diversity of aquatic environments throughout the province. The process should further distinguish what water uses are practical and what level of temperature modification is acceptable within the diversity of existing temperature regimes provided in nature. The procedure for developing a classification system will be expanded upon in greater detail in Section 8.
In consideration of the protection requirements of specific water uses, guideline development should adopt an ecosystem-based approach wherein the array of potential designated water uses complement or support the single use with the most stringent temperature criteria applied to each classification. That is, allowable temperature modifications from human activities associated with one use should not compromise the protective needs of an alternative use within the same classification. Moreover, it is critically important that cumulative effects of human activities/uses on water temperature be considered holistically and not individually. This is particularly important in light of management decisions to allow future developments to proceed if existing uses already compromise the attainment of a desired guideline. If guidelines are to be considered within an ecosystem context, then all beneficial uses should be accommodated within the temperature regimes provided in nature.
6.1 Drinking water
The numerical guideline value (less than or equal to 15 degrees C) prescribed by Health and Welfare Canada (1998) and adopted by the Ministry of Environment, Lands and Parks (1998) should be maintained as an aesthetic objective. To date, guideline improvement based on evidence in the scientific literature has not been shown and the current guideline is consistent with other jurisdictions in the Pacific Northwest.
6.2 Recreation and aesthetics
The numerical guideline (15-30 degrees C) provided on behalf of Health and Welfare Canada (1992) is recommended on an interim basis in place of the narrative statement provided on behalf of Ministry of Environment, Lands and Parks (1998; after CCME 1999) which states, "the thermal characteristics of water should not cause an appreciable increase or decrease in the deep body temperature of bathers and swimmers". Elevated temperatures in excess of 30 degrees C provide optimal conditions for blue-green algal blooms; toxins produced by certain strains of blue-green algae have been linked to illness in humans (CCREM 1987). Future recreation guidelines should consider primary and secondary contact criteria (e.g., Washington State 1997) following the development of water use classifications.
6.3 Aquatic life
6.3.1 Freshwater
Current BC temperature guidelines for the protection of freshwater aquatic life specify an allowable increase or decrease of 1 degrees C from seasonal, background conditions in the environment (Nagpal et al. 1998). Temperature guidelines are further included to protect specific life history stages of salmonids: juvenile and adult rearing, 18 to 19 degrees C (maximum weekly average); maximum water temperatures between 22 and 24 degrees C; adult spawning, 8 to 10 degrees C (maximum weekly average); and egg incubation, 13 to 15 degrees C (maximum). In keeping with the lowest-observable-effects level protocol (CCME 1999), the process of setting temperature guidelines necessarily involves satisfying the needs of the most sensitive species. As outlined above, salmonids are cold-water dependent and exhibit a narrow range of cold temperatures to meet their life history requirements. Accordingly, the range of water temperatures encountered in the wild play a critical role in determining their overall distribution and abundance. Of the native species described, rainbow trout are considered to have the lowest thermal sensitivity and bull trout the highest. Given the current BC guidelines, existing temperature criteria are not considered optimal to meet the protective needs of all life stages or all fish species. Specifically, maximum temperature allowances for juvenile exposure in the range of 22-24 degrees C and incubation temperatures up to 15 degrees C are considered inappropriate. Temperatures in the range of 22-24 degrees C represent the thermal limits to salmonid distribution and acceptance of these threshold values place individual species at much higher risk. As demonstrated above, criteria that exceed optimum temperatures have serious implications on growth/development, disease resistance, reproduction and species interactions. Based on the review of the literature to date, maximum temperature allowances between optimum and incipient lethal levels suggest that individual species will experience an impairment threshold (i.e. net zero growth or cumulative effects leading to death; McCullough 1999). Biophysical surveys documenting fish distribution in the wild suggest that maximum temperature tolerances are always less than the upper incipient lethal level (Eaton et al. 1995). Allowances set beyond optimum temperatures, therefore, will likely affect fish production by forcing species to utilize less productive environments (i.e., headwaters) in their search for temperature preferences. Consequently, regulations designed to accommodate tolerance limits will ultimately force fish production well below maximum population density.
Given the range of temperatures for specific life history stages among all salmonid species encountered in British Columbia, the selection of a single criterion to meet the temperature requirements of all species is considered exceedingly difficult. Moreover, for any one species, physiological optima occur over a range of temperatures rather than at a single value. Therefore, temperature guidelines that closely follow the physiological optima of a particular life stage for an individual specie will likely provide maximum protection where a species presence has been previously determined. Based on the availability of fish presence/absence information throughout the province, a known versus unknown fish distribution approach to guideline development is recommended: As an interim measure for streams where fish presence is suspected but unconfirmed, summer rearing conditions should not exceed a mean weekly maximum temperature (MWMT - see below) of 18 degrees C and the maximum daily temperature should not exceed 19 degrees C. Similarly, incubation temperatures for eggs deposited in late spring and early fall should not exceed 12 degrees C. Where fish distribution information is available, then mean weekly maximum water temperatures should only vary + or - 1 degrees C beyond the optimum temperature range of each life history phase (incubation, rearing, migration and spawning) for the most sensitive salmonid species present (refer to Table 6). The proposed general guideline lies within the temperature tolerance limits for salmonids (refer to Table 2), extends to the upper temperature limit for positive growth (Armour 1991) and minimizes the period of exposure at the boundary limit (average maximum temperature over 7 consecutive days). The upper limit of 12 degrees C for incubation lies below the tolerance limit for those species having incubation periods that overlap either early or late summer when embryos are potentially at highest risk. Failure of complete egg development has been experimentally determined where temperatures exceed 13 degrees C for the more sensitive species (refer to Table 1). The general guideline is only intended for use as a default when fish presence is unknown. The majority of watersheds supporting industrial activities that could otherwise alter background temperature regimes in streams have resource inventory information presently available. Alternatively, new industrial projects would require a full environmental assessment that would provide a complete listing of aquatic resources. The specie-specific guideline variance of 1 degrees C places an upper and lower limit at the boundary of the optimum temperature range for each life history stage, allows for seasonality by encompassing temperature optima for individual life stages and avoids tolerance limits that could otherwise
Table 6. Optimum temperature ranges of specific life history stages of salmonids and other coldwater species for guideline application.
contribute to chronic sub-lethal effects during summer maxima. The guideline offers consistency in its approach by recognizing the most sensitive species in the stream ecosystem. Moreover, the guideline is highly amenable to regional adjustments in species-specific temperature optima owing to differences in latitude or elevation across the province that may influence a species' local adaptation to ambient temperature regimes. Finally, because of the close relationship between behavioural thermoregulation in fish and thermal optima, the incorporation of optimum temperatures as a guideline seems highly appropriate since final temperature preferenda often coincide with temperature optima for a variety of species and age classes within a species (Kellogg and Gift 1983; Jobling 1981; Brett 1971). Thermal optimization has been shown to confer a selective advantage (i.e. capacity adaptation) whereby salmonids that occupy discrete thermal gradients maximize their scope for activity and ultimately enhance survival (Evans 1990; Bryan et al. 1990).
The choice of mean weekly maximum temperature as the most appropriate temperature metric is further recommended since fluctuating temperature regimes that exceed incipient lethal levels may place populations at further risk where maximum limits are calculated from maximum weekly average temperatures (MWAT). Although MWAT has been widely used in previous guideline documents (Nagpal et al. 1998; CCME 1999), the application of this metric can be biologically criticized for the peak temperatures that they average away (McCullough 1999). The MWAT calculation has been shown to sacrifice some level of production and not provide adequate protection (Hokanson et al. 1977 cited in McCullough 1999). For example, a recommended MWAT of 17 + or - 2 degrees C for rainbow trout was insufficient to facilitate maximum yield; a reduction of ~27% of the normal production was observed under conditions of a fluctuating temperature regime. Use of the 7-day average maximum temperature (or the average of the warmest daily maximum temperatures for 7 consecutive days (MWMT)) is recommended since the 7-d average maximum is generally 0.5 to 2.0 degrees C lower than the highest daily maximum temperature in summer (Buchanan and Gregory 1997) and the mean difference between MWMT and MWAT is about 3 degrees C based on a comparison of metrics conducted on 73 streams in Idaho and Montana (Hillman and Essig 1998). This consideration is particularly important relative to cumulative effects if fish are repeatedly exposed to maximum temperatures above critical limits over brief periods. To this end, an allowance for the frequency of exceedence must be taken into consideration to reduce the risk of cumulative stress leading to death, disease, poor reproductive success or poor growth. The 7-day average maximum is consistent with protocols established by Oregon (ODEQ 1996), and the approach is consistent with guidelines specified by Oregon, Washington and Idaho (refer to Appendix 1-3). The MWMT has been recently supported by the US Environmental Protection Agency (EPA 1997) and the US Forest Service Inland Native Fish Strategy (USFS 1995). Since the downstream limits to fish distribution are linked to maximum temperatures attained within specific reaches, the recommended maximum temperature guideline is expected to support the maximum productive capacity of stream environments for salmonids in British Columbia. The interim guidelines recommended above are not considered fully adequate for the protection of bull trout. In consideration of their blue-listed status in BC, specific temperature guidelines are recommended for waters frequented by bull trout. To this end, maximum daily temperatures should not exceed 15 degrees C, maximum spawning temperatures should not exceed 10degrees C, and incubation temperatures should not exceed 6 degrees C or fall below 2 degrees C. The sensitivity of survival rate to a 1 degrees C decrease in winter is much greater than a corresponding increase in summer, when temperatures lie at the extreme of optimum seasonal ranges (McCullough 1999). Therefore, no measurable temperature modification (i.e., increase or decrease) during the period of incubation should be allowed. Optimum juvenile rearing temperatures fall within the range of 6-14 degrees C. While bull trout distributional information for daily maximum temperature exceeding 20 degrees C exist for watersheds in their southerly range in North America (Adams 1994; Gamett 1998), short-term exposures to these critical levels are not considered conducive to normal growth or survival. These recommendations are consistent with the range of temperature criteria specified for bull trout in Oregon (ODEQ 1996) and Idaho (IDH&W 1998; refer to Appendix 1-3).
The justification for special guidelines for bull trout has been aptly summarized by Buchanan and Gregory (1997) and is highly applicable to regions of British Columbia affected by hydro-electric development:
"Most cold-water species such as bull trout were distributed more widely during previous glacial periods of lower temperatures across the North American continent. Current populations commonly are patchy and restricted to cold water refuges. Gene flow between populations is minimal, and local populations are easily isolated by impacts on stream flows and temperatures. The extreme temperature constraints on cold water species limit them to restricted or marginal habitats in the headwaters of river drainages and scattered outlets of deep cold water aquifers. To protect these species, water temperature standards must be substantially lower than traditional criteria, and must accommodate seasonal requirements of specific life history stages." This same approach is recommended for British Columbia to protect cold-water species at all stages of their development.
Dolly Varden (Salvelinus malma), once thought to be the same species of char as bull trout, display similarities to bull trout in their choice of habitat within British Columbia. Temperature preferences for rearing also show a close parallel (Tables 2 and 6). Based on these similarities, it is recommended that Dolly Varden be afforded the same special protection as bull trout, since their close relationship suggests that both species may be equally sensitive to thermal variations.
Much of the rationale for a temperature guideline to protect aquatic life has centered on the avoidance of temperature extremes that have either acute or chronic consequences. Equally important, however, is the need to identify an acceptable rate of temperature change that does not invoke a physiological response that contributes to mortality. The experimental evidence suggests that the response to thermal shock is highly dependent on the acclimation temperature (both constant and cyclic), the magnitude of the temperature shift and the final endpoint value (Threader and Houston 1983; Thomas et al. 1986; Tang et al. 1987). Beyond the obvious consequences of an instantaneous temperature change that leads to death within minutes, experimental designs that impose a large amplitude of diel variation can also have lethal effects when fluctuations lead to increased widening of the diel range (Thomas et al. 1986). Sub-lethal effects over a narrower range in delta T that lead to either heat shock or cold shock (i.e. rapid increase or decrease) can include physiological stress leading to metabolic dysfunction (Wedemeyer 1973), growth inhibition and disease initiation (Wedemeyer and McLeay 1981) or increased predation (Coutant 1973). Slower rates of heating or cooling expose fish to temperatures within their tolerance range and provide a period of acclimation to facilitate physiological adjustment (McCullough 1999).
Rapid increases associated with diel fluctuation would not be expected to occur in nature since daily variation in temperature of about 3 degrees C has been reported for streams in an undisturbed old growth forest (Thomas et al. 1986); a diel fluctuation (minimum to maximum) which is equivalent to about a 0.4degrees C change per hour. In the same study, a higher rate of heating of about 1.95 degrees C/h was observed for streams associated with clear-cuts. The fact that salmonids have adapted to small rates of change in natural ecosystems suggests that alterations in stream temperature imposed by anthropogenic sources should follow the same template provided in nature. To this end, a rate of temperature change in the order of 0.5 to 1.0 degrees C/h is recommended for guideline purposes. Experimental support for this recommendation is further provided from a study on the effect of rate of temperature increase on salmonid parr (Elliott and Elliott 1995). In a series of tests to determine the CTM at nine different rates of temperature increase (i.e. 0.0104 - 18 degrees C/h), rapid recovery of fish, returned to suitable temperatures before death occurred, was only observed for rates up to 2 degrees C/h.
Continued application of the + or - 1 degrees C change from natural conditions is expected to meet the protection needs of aquatic life in natural lake environments. The availability of water temperature in a range, which is physiologically optimal, has also been demonstrated to contribute strongly to a species productive capacity within a lake environment (Christie and Regier 1988). Further definition is required on the size of acceptable mixing zones associated with point-source discharges to lakes or rivers before temperature guidelines are formalized. Mixing zone boundary considerations should be resolved with future deliberations aimed at water use classifications.
In summary, recommended guideline changes for the protection of aquatic life in streams include:
· temperature metrics to be described by the 7-d average maximum temperature or mean weekly maximum temperature (MWMT)
· where fish presence is unknown, salmonid rearing not to exceed MWMT of 18 degrees C; maximum daily temperature not to exceed 19 degrees C and;
· maximum temperature for salmonid incubation from June until August not to exceed 12 degrees C;
· where fish presence is known, mean weekly maximum water temperatures should not exceed + or - 1 degrees C beyond the optimum temperature range for each life history phase of the most sensitive salmonid species present (refer to Table 6 for temperature optima)
· the rate of temperature change in natural water bodies not to exceed 1 degrees C/h.
Specific to bull trout and Dolly Varden in streams:
· maximum daily temperatures for rearing should not exceed 15 degrees C;
· maximum spawning temperature should not exceed 10 degrees C;
· preferred incubation temperatures should range from 2- 6 degrees C In lakes:
· + or - 1 degrees C change from natural condition
6.3.2 Marine
The numerical standard (+ or - 1 degrees C from natural background condition) recommended by CCME (1999) and cited as a working guideline by the Ministry of Environment, Lands and Parks (Nagpal 1998), should be maintained to minimize impacts on marine resources. The following narrative statements included in the CCME (1999) recommendation should also apply, "The natural temperature cycle characteristic of the site should not be altered in amplitude or frequency by human activities. The maximum rate of any human-induced temperature change should not exceed 0.5 degrees C per hour". To date, guideline improvement based on evidence in the scientific literature has not been shown and the current guideline is consistent with other jurisdictions in the Pacific Northwest (e.g., Alaska; refer to Appendix 1-4).
6.4 Wildlife
At present, there is no guideline value or narrative statement for the protection of wildlife in British Columbia. As an interim measure, the numerical guideline of + or - 1 degrees C from natural background condition should apply until the recommended water use classification (section 8) is completed. Future recommendations for the protection of wildlife should be considered within an ecosystem context; recommendations should complement temperature guidelines developed for the most sensitive use within specific classifications. A scaled model of temperature criteria for the protection of wildlife is provided by Washington State, where increasing temperature allowances mirror the shift from cold water to cool water environments (refer to Appendix 1-7).
6.5 Irrigation and livestock watering
At present there is no guideline value or narrative statement for the protection of irrigation or livestock in British Columbia. As an interim measure, the numerical guideline of + or - 1 degrees C from natural background condition should apply until the recommended water use classification (section 8) is completed. Future recommendations for the protection of irrigation or livestock should be considered within an ecosystem context; recommendations should complement temperature guidelines developed for the most sensitive use within specific classifications. A scaled model of temperature criteria for the protection of irrigation and livestock is provided by Washington State where increasing temperature allowances mirror the shift from cold water to cool water environments (refer to Appendices 1-5 and 1-6).
6.6 Industrial use
At present there is no guideline value or narrative statement for the protection of industrial use in British Columbia. As an interim measure, the numerical guideline of + or - 1 degrees C from natural background condition should apply until the recommended water use classification is completed. Future recommendations for the protection of industrial use should be considered within an ecosystem context; recommendations should complement temperature guidelines developed for the most sensitive use within specific classifications. A scaled model of temperature criteria for the protection of industrial use is provided by Washington State where increasing temperature allowances mirror the shift from cold water to cool water environments (refer to Appendix 1-8).