A variety of land-based developments or industrial activities in British Columbia have the potential to affect the temperature of surface or ground water supplies through either direct or indirect means. Freshwater is utilized in various process applications in industry (Manahan 1991) and, following treatment, effluent can be released as a point source discharge to surface waters. As part of the treatment process, waste water is often stored in lagoons or settling basins for the purpose of aeration, filtration and clarification. Depending on time of year, the treated effluent may be warmer than its attendant receiving environment and hence, the downstream zone of influence may be altered spatially on a seasonal basis. Monitoring activities to date however, have concentrated on toxic constituents in effluents rather than temperature effects due to the dilution characteristics of most receiving environments relative to the rate of effluent input (L. E. McDonald, Environmental Protection, Cranbrook, BC; pers. comm.). Industrial and municipal examples include smelting, chemical manufacturing, petrochemical refining, pulp and paper processing, thermal power generation, underground and surface mining, and sewage treatment. With respect to the pulp and paper industry, research has traditionally focused on the lethal and sub-lethal effects of pulp mill effluent on aquatic biota; exposure studies on fish have been directed toward the secondary effect of effluent on high temperature tolerance ability among salmonids under ambient conditions (Thut and Schmiege 1991). It is important to recognize that storage of untreated effluent in lagoons following initial discharge from the plant effectively reduces high temperatures normally associated with process water. Thermal shock to biota in receiving waters has only been reported under conditions of an accidental spill (Walden and Howard 1974). Alternatively, the direct discharge of cooling water associated with certain industrial activities may effect the zone of influence over short time intervals since the rate of temperature change may be much more dramatic due to the greater temperature differential between the effluent and the environment. The degree of impact on the receiving environment is again dependent upon the size of the water body and time of year. Heat exchange processes are more commonly associated with the smelting and thermal-electric generation industries.
Non-point source temperature effects are encountered at a much larger spatial scale and are generally associated with natural resource development activities that alter ecosystem structure and function. Examples include forestry, mining, and hydro-electric and community water supply development. Water temperature in streams can be affected by forestry operations in two principal ways: 1) removal of streamside shading that increases direct solar heating (Beschta et al. 1987) and 2) modification of hydrologic processes that regulate the quantity and timing of streamflow (i.e., precipitation, infiltration, evapotranspiration, storage and run-off; Swanston 1991). Heat transfer occurs in direct proportion to the amount of solar radiation reaching the water surface and as a function of a stream's channel geometry (Chamberlin et al. 1991). Although volume and turbulence can affect temperature, depth has been shown to have an over-riding influence relative to basin elevation (Adams and Sullivan 1989; Caldwell et al. 1991 cited in Teti 1998). Partial stratification of deep pools helps moderate heat transfer and the combination of overstream cover and deep pool habitat help determine the magnitude of diurnal or seasonal temperature fluctuation. A lower channel stability following riparian harvesting is manifested through increased width:depth ratios due to channel widening and increased sediment input, as well as reduced pool to riffle ratios as structural elements become depleted (Bisson et al. 1987; Chamberlin et al. 1991). In the absence of shade and large residual pool volumes, summer stream temperatures have increased (Holtby 1988; Brownlee et al. 1988). Increased stream temperature effects are expected to occur in the mid to lower reaches of a watershed since water temperature maxima are strongly influenced by elevation; further increases above a maximum equilibrium temperature in headwater areas are unobserved despite higher ambient air temperature (Caldwell et al. 1991 cited in Teti 1998). As a consequence, timber harvest-related temperature effects within first order headwater streams are expected to have minimal impact on downstream higher order stream reaches (Doughty and Sullivan 1991; Caldwell et al. 1991 cited in Teti 1998).
Timber harvesting has been linked to changes in water quality, water quantity and timing of streamflow with a wide degree of variation in hydrologic responses that can be related to the method and extent of harvesting within a particular basin. The effects of forest practices can influence snow accumulation and melt rate, evapotranspiration and soil water, as well as water infiltration into, and transmission rate through, forest soils (Chamberlin et al. 1991). With a higher accumulation of snow and faster rate of melt contributing to a higher run-off from cut-blocks (Toews and Gluns 1986), the degree of ground water recharge has been shown to increase or decrease depending upon the amount soil compaction associated with harvesting activities that affect its infiltration capacity. (Greacen and Sands 1980; Hetherington 1988; Hartman and Scrivener 1990). Since stream temperature can be moderated by ground water input, changes in ground water supply can either stabilize or alter the thermal regime.
Similar changes in the water balance have been attributed to surface mining operations owing to largescale landscape modification (i.e., vegetation removal and soil disturbance). Stream temperature can be affected by interception and redirection of surface flows or disruption of entire aquifers (Nelson et al. 1991). Moreover, both non-metallic or metallic ores require large volumes of water for processing and depending upon availability from surface supplies, potential dewatering of channels during periods of low summer flow can elevate stream temperatures dramatically. Effluents from smelters or concentrators or shallow tailings ponds and settling basins may be considerably warmer than attendant receiving waters; particularly in settling ponds where fine (black) sediments absorb heat. The downstream zone of influence is again variable depending on the rate of discharge relative to the size of the receiving body.
The impoundment of large or small rivers and streams for the purpose of hydro-electric development or community water supply can effect the thermal regime of the systems' pre-impoundment condition and potentially alter the thermal regime of downstream reaches. Seasonal temperature profiles in reservoirs are highly variable and dependent upon complex hydrodynamics relative to tributary inflow, basin morphometry, drawdown and discharge characteristics (Wetzel 1975), as well as degree of stratification. In summer, elevated temperatures in epiliminial waters released through a spillway can increase downstream river temperatures, whereas a decrease can be expected if cooler hypolimnial waters are released through turbines or sluice gates. The opposite effect is generally observed in winter due to density/temperature gradients associated with the degree of limnetic stratification. Conversely, run-of-the-river type reservoirs that typically display much shorter retention times, are less susceptible to stratification and often parallel temperature characteristics of upstream reservoir releases (US Army Corps of Engineers 1999). Diurnal or seasonal differences in the thermal regime of downstream reaches are therefore strongly related to operational regimes of individual dams in response to hydro-electric demand, storage for flood control/water supply or demand for downstream water use. Both daily and seasonal dynamics in dam operations have the potential to alter background temperature patterns associated with the river's pre-impoundment condition (Oliver and MacDonald 1995).
Agricultural use of water or rangeland use associated with small streams and their riparian areas is widespread throughout the province. Water extraction during the period of low summer flow and unrestricted livestock grazing in streamside environments have also been shown to have indirect effects on stream temperature (Platts 1991; Rinne 1999). Small streams that support the irrigation needs of adjacent croplands can often lead to lowering of stream flow and elevated temperatures in summer, particularly where irrigation demand is high, water supply is limited and over-licensing has occurred. Improper range management practices that have led to over-grazing of riparian areas have ultimately been responsible for changing, reducing or eliminating vegetation or modifying stream banks (i.e., trampling by livestock). The removal of overstream (vegetation) and degradation of instream (undercut banks) cover have reduced the amount of shading and led to increased solar heating (Armour 1977; Benke and Zarn 1976; and Platts 1983 cited in Platts 1991). In British Columbia, the most sensitive stream ecosystems affected by range management practices are likely associated with arid regions of the south and central interior where thin soils and sparse grasslands are easily disturbed and recovery periods are long.