The state of water quality was assessed by comparing values obtained for each variable to BC Environment's approved and working guidelines for water quality (Nagpal et al., 1998a,b), as well as to site-specific objectives set by the BC Environment. (Guidelines were formerly called criteria, and the older term has been used in many of the figures in this report.) Assessment of the data was based entirely on visual interpretation of the graphed variables. The following variables easily met guidelines or objectives and showed no environmentally significant trends: barium, beryllium, boron, dissolved chloride, hardness, magnesium, molybdenum, nickel, ammonia, nitrate/nitrite, pH, specific conductivity, dissolved sulphate, and vanadium. Guidelines or objectives were not available for the following variables, nor were potentially significant trends apparent: bismuth, dissolved ortho-phosphorus, silica, strontium, tellurium, tin, and zirconium. Minimum detectable limits were too high to permit comparison to all or some of the guidelines for: antimony, arsenic, cadmium, chromium, cobalt, copper, lead, selenium, silver, thallium, and zinc. Variables discussed below displayed levels that were potentially detrimental to such uses as drinking water, recreation, irrigation, agriculture, aquatic life and wildlife, or merited some explanation.
Flow (Figure 3) values showed consistent seasonal variations, with highest annual flow in the spring freshet and early summer, and lowest in the winter. The river was free flowing, with no intervening lakes, and thus was noticeably affected by snowmelt and rainfall. Flow monitoring should continue because of its importance in interpreting water quality indicators.
Total aluminum (Figure 4) met the 0.2 mg/L dissolved guideline for drinking water, and the 0.1 mg/L dissolved guideline for aquatic life at least 47% and 27% of the time, respectively. The 0.05 mg/L average dissolved guideline for aquatic life was not met at all. Nordin and Holmes (1993) noted some unexpectedly high values for aluminum in this river. High aluminum and high non-filterable residue values (Figure 35) usually occurred together, suggesting that the aluminum was in a particulate form and not likely biologically available, and would be removed by the treatment needed to remove turbidity before drinking. Since the guidelines used are for dissolved aluminum, which would likely be much lower than the total aluminum values collected, the attainment of guidelines was probably much greater than indicated above. Dissolved aluminum should be measured in future for appropriate comparison to the guidelines.
Calcium (Figure 12) values showed that the North Thompson River was quite well buffered against acid inputs. Lower values in spring and early summer occurred as a result of dilution during freshet from snowmelt, which has a low calcium content.
Total chromium (Figure
14) values remained well below the guideline for drinking water, and the
aquatic life guideline for trivalent chromium, but exceeded aquatic life guideline
for hexavalent chromium once, on May 19, 1993. Flow (Figure
3) and non-filterable residue (NFR)
(Figure 35) were also high on this date during spring freshet, indicating that the chromium was probably in a particulate form, and not biologically available. This value could also have been a false positive, close to the 0.002 mg/L minimum detectable limit. Dissolved chromium should also be measured and a lower minimum detectable limit (_0.0001 mg/L) should be used. Measurements of trivalent and hexavalent chromium may be needed if dissolved or total chromium values exceed the aquatic life guidelines.
Fecal coliforms (Figure 16) met all guidelines, except the 10/100 mL site-specific objective and guideline for raw drinking water receiving disinfection only, which was exceeded 27% of the time. E. coli (Figure 19) also exceeded the raw drinking water objective for water receiving disinfection only (<10 - 90th percentile), most notably at times of high flow during the early summer freshet of 1993 and 1994. This indicates that the water should be partially treated and disinfected prior to consumption. Higher levels of these indicator organisms generally occurred during periods of high flows and non-filterable residue in spring and early summer (Figures 3 and 35), suggesting that fecal coliform levels may have been related to agricultural runoff during high flows. When Westsyde was sewered in 1993-94, a substantial amount of contaminated ground water was removed from the foreshore of the North Thompson (Grace, 1996). At the Sun Peaks Resort, sewage treatment will likely not become a major water quality issue until about half way through the projected development (Grace, 1996). Both fecal coliforms and E. coli should continue to be monitored as a measure of fecal contamination in the river, and the frequency of monitoring should be increased to at least five times in 30 days for better comparison to the objective.
Total absorbance colour (Figure 17) consistently met the 100-unit maximum true colour recreation guideline, but exceeded the 15-unit true colour drinking water and desirable recreation guideline once, on April 19, 1994 during spring freshet when non-filterable residue levels were high. The values cannot be directly compared to the true colour guidelines since total absorbance colour is measured differently than true colour. True colour should be measured to permit direct comparison to the guidelines, and to provide the background levels for the true colour objective for the Thompson River (Nordin and Holmes, 1993).
Total copper (Figure 18) values exceeded the 0.002 mg/L guideline for aquatic life three times. One of these dates, May 19, 1993, had a high non-filterable residue level (Figure 35), suggesting that the copper was in a particulate form and was probably not biologically available. The copper levels on October 26, 1993 and March 23, 1995 occurred during lower flows and non-filterable residue levels, suggesting that the copper may have been bioavailable. These data compare favourably with Nordin and Holmes (1993), who found some unexpectedly high copper values. Samples were collected less often than the required five samples in 30 days for proper comparison to guidelines, and thus increased frequency of measurements is recommended for total and dissolved copper. The minimum detectable limit should be lowered to at least one- tenth of the guideline. Field blanks and replicates should also be collected to assess the potential for artificial contamination.
Hardness (Figure 20) values indicate that the water was relatively soft (30-60 mg/L) and below the optimum level for drinking water, but still quite acceptable. Hardness should continue to be monitored due to its influence on metal toxicity, and dissolved organic carbon should be added for the same reason.
Total iron (Figure 21) consistently met the 5 mg/L guideline for irrigation, but exceeded the guideline for drinking water (aesthetics) and aquatic life (0.3 mg/L) 63% of the time. Usually, higher levels of iron and non-filterable residue (Figure 35) occurred together, indicating that the metal was in particulate form, was probably not biologically available, and would be removed by treatment needed to remove turbidity before drinking. Given that the average concentration of iron in the Earth's crust is 56,300 mg/kg (Demayo, 1992), as little as 5.5 mg/L of non-filterable residue could cause the 0.3 mg/L guideline to be exceeded. However, the guideline was also exceeded at times when non-filterable residue was low. Given the lack of anthropogenic sources of iron, and since levels have been high since monitoring began in 1987, we speculate that iron levels were probably naturally high in this river. Total and dissolved iron should be monitored.
Total manganese (Figure 24) levels were generally well below most guidelines, but slightly exceeded the drinking water (aesthetics) guideline twice, during spring freshet. Since non-filterable residues (Figure 35) were also elevated at these times, the manganese was probably in particulate form and would be removed by the treatment needed to remove turbidity before drinking.
Molybdenum (Figure 25) exceeded the irrigation guideline on August 24, 1987, but this value may well have been a false positive, being close to the minimum detectable limit. Since 1988, levels have remained below the guideline.
Total Kjeldahl Nitrogen (Figure
28) values were highest during spring freshet, when flow (Figure
3) and fecal coliform (Figure 16) levels were
highest, implying a link to agricultural runoff. Higher levels could also have
been due to increased instream periphyton biological production in the spring
to summer months. Nordin and Holmes (1993) noticed slightly increasing values,
but there are no trends apparent in our data
Total phosphorus (Figure 31) peak values occurred when suspended sediments (non-filterable residue) were elevated (Figure 35) during freshet due to increased erosion and agricultural runoff. The dissolved phosphorus measurements discussed below indicate that most of the total phosphorus was in a particulate form and probably not readily bioavailable. This variable should continue to be monitored as an indicator of nutrient loadings to Kamloops Lake.
Low-level dissolved ortho-phosphorus (Figure 32) concentrations showed no consistent patterns or trends. There was little similarity to other measures of dissolved phosphorus [total dissolved phosphorus and dissolved ortho-phosphorus (Figures 33 and 34)], possibly since all the values were close to the minimum detectable limits (MDL). Uncertainty in the values is high close to the MDL (levels were less than nine, three and two times above the MDL's for each variable, respectively). Low-level dissolved ortho-phosphorus has the lowest MDL, and thus it should continue to be monitored as the measure of bioavailable phosphorus.
The non-filterable residue (NFR) (i.e., suspended solids or sediment) (Figure 35) fisheries guideline was exceeded 26% of the time. The turbidity (Figure 46) values were always below the guideline for recreation, but exceeded the 5 and 1 NTU guidelines for drinking water 35% and 89% of the time, respectively. Higher levels of both variables occurred most often during times of highest flows, in spring freshet, and during early glacial melts, due to enhanced erosion. Turbidity removal (e.g., filtration) plus disinfection are needed prior to drinking water use. When Westsyde was sewered, in 1993-94, major residential infilling occurred, potentially causing increased erosion and sediment production. In addition to this, the large subdivision and golf course complex built near Westsyde on the banks of the North Thompson could have impacted water quality in terms of increased erosion and urban run-off entering the river (Grace, 1996). Similar impacts could be expected for the Sun Peaks Resort expansion. Since 1993, however, turbidity and NFR results have been stable, although the data were rather sparse. There were no apparent trends in NFR or turbidity during 1987-95. These variables should continue to be monitored to assess potential impacts on water quality as a result of erosion.
Total titanium (Figure 45) exceeded the drinking water and aquatic life guideline once, on May 19, 1993, a time of high flows (Figure 3) and non-filterable residue levels (Figure 35) during spring freshet. Thus, the metal was probably not biologically available, and would be removed by the treatment needed to remove turbidity prior to drinking. Levels have remained below guidelines since then.
Artificial contamination of samples of total zinc (Figure 48) occurred during 1993-1995. Prior to 1993, levels were below the maximum aquatic life guideline except on March 30, 1987, a time of low non-filterable residues (Figure 35). The MDL was too high to evaluate attainment of the average aquatic life guideline. Nordin and Holmes (1993) noted some unexpectedly high values for zinc in the river. Total and dissolved zinc with a lower minimum detectable limit (e.g., _0.001 mg/L) should be measured to establish the zinc levels in the river. Field blanks and replicates should also be collected to assess the potential for artificial contamination.