A review of the guideline approach in the majority of jurisdictions in the PNW has revealed that most US states have opted for a water use classification system that recognizes the diversity of water resource values provided in nature, identifies what beneficial uses are appropriate for each classification, and assigns specific guidelines for their individual protection. The same approach is recommended for British Columbia to offer greater flexibility in the designation of beneficial uses by fine-tuning guidelines that provide appropriate levels of protection to water resources of varying environmental quality. An ecosystem-based model for the derivation of classifications is similarly recommended to ensure that individual designated uses complement and support the most sensitive use.
The classification of watersheds across the province is in no way a small task. The challenge to such an undertaking is to apply a classification system that is simple, cost-effective and region-specific. Consistent with other jurisdictions, the classification approach could employ a series of classes based on environmental quality (e.g., Class AA (extraordinary), A (excellent), B (good) or C (fair); Washington State) or adopt a cold water (up to 20 degrees C), cool water (up to 25 degrees C), and warm water (up to 30 degrees C) designation.
The characterization of streams and rivers of variable size throughout the province could be accomplished by a variety of means. In consideration of the existing temperature records available through federal and provincial programs or local community watershed or stewardship groups, it may be possible to categorize a number of streams based on previously recorded summer maxima. In areas where water temperature information is lacking, estimates could be derived from air temperature records. For example, based on field studies of the air-water relationship, Stefan and Preud'homme (1993) found weekly water temperature changes to average 0.86 of the weekly air temperature changes for streams of various sizes in southern and northern US states (Eaton and Scheller 1996). The method could be applied to unrecorded streams where air temperature data from nearby climate stations are available. Accuracy of the estimate could be further improved by a simple field measurement. Stoneman and Jones (1996) were able to classify representative streams in Ontario by simply comparing water temperature to air temperature at 16:00 h on hot summer days. Maximum daily water temperatures corrected with air temperature were highly effective in establishing the thermal stability of selected streams and separating observations into discrete classifications with limited overlap. The same process could be duplicated in BC with the assistance of seasonal staff or stewardship groups, particularly in community watersheds. A third method that would lend itself to development of specific temperature guidelines for streams characteristic of different fish guilds, is the field information-based system for estimating fish temperature tolerances (Eaton et al. 1995). The method involves a technique for spatial and temporal matching of stream temperature records and fish sampling events to establish annual temperature regimes for freshwater fish (i.e., the Fish and Temperature Database Matching System (FTDMS)). The 95th percentile of the weekly mean temperatures is used to estimate the maximum temperatures tolerated by a particular species in nature (Eaton et al. 1995). This same approach could be used to separate cold water salmonid streams from other cool water or warm water streams colonized by non-salmonid fish species. Datasets for fish/temperature series could be accessed from the BC Fisheries Branch Fish Information Summary System (FISS) to determine species presence/absence throughout the year. The number of stream records in the FISS database has increased dramatically in most regions since promulgation of the Forest Practices Code. Maximum temperature estimates could be acquired from sources identified above. The technique has two principal benefits: 1) it allows temperature tolerance guidelines to be based on temperature preferential displayed by representative fish species in nature and avoids reliance on incipient lethal limits determined under laboratory conditions and 2) it lends itself to an ecosystem-based approach wherein temperature guidelines are developed in consideration of the most sensitive use. Guidelines for temperature would therefore follow the temperature tolerances of representative fish guilds within discrete classifications; other beneficial water uses would be included within the same temperature range to complement the most sensitive use (i.e., fish). The development of class-specific temperature guidelines and inclusion of designated uses within each class are therefore derived from the variation of environmental qualities provided in nature and is consistent with classification systems adopted in Washington, Oregon, Idaho and Montana.
The future development of temperature-specific guidelines for water use classifications across the province is paramount given the threat of surface water temperature increases due to global warming. Historical summaries comparing the effect of climatic condition on annual growth (King et al. 1999), experimental manipulations of the thermal regime of stream environments (Hogg et al. 1995; Hetrick et al. 1998), or the application of simulation models (Van Winkle et al. 1997), suggest that the effects of temperature increase on annual temperature cycles will have positive and negative impacts on aquatic biota relative to growth, reproductive success, physiological condition and population genetics. Negative impacts in aquatic environments are anticipated with temperature shifts as little as 2 to 4 degrees C. These events place a larger burden on management agencies to minimize temperature perturbations associated with smaller-scale human activities within individual basins. It is suggested that the water use classification approach is an important step in improving the temperature guideline process and deriving region-specific guidelines that provide adequate levels of protection throughout the province. To facilitate the guideline development process, it is further recommended that the utility of derivation methods such as the air-water relationship or FTDMS be tested for ease of application over a smaller geographical area before it is given province-wide application. Vancouver Island seems a logical choice in consideration of the diversity of anadromous and resident fish species present, diversity of development activities in watersheds, expected diversity of stream temperature regimes due to latitudinal position and elevation, and temperature data records. Following the development of a classification system, temperature guidelines should be developed for individual beneficial uses within each classification. Guideline examples provided by PNW jurisdictions are highly recommended to facilitate this process.