3. State of the Water Quality
The state of the water quality was assessed by comparing the values to the water quality objectives for the South Thompson River (Nordin & Holmes, 1992) and to B.C.'s Approved Guidelines and 1998 Compendium of Working Guidelines for water quality (Nagpal et al., 1998), and by looking for any obvious trends in the data. Any levels or trends that were found to be deleterious or potentially deleterious to sensitive water uses, including drinking water, aquatic life and wildlife, recreation, irrigation, and livestock watering were noted in the following discussion. The following water quality indicators were not discussed as they easily met all water quality objectives or guidelines and showed no clearly visible trends: total barium, total inorganic carbon, total absorbance colour, specific conductivity, magnesium, total manganese, nitrogen (ammonia, Kjeldahl, nitrate, nitrate/nitrite, total, and total organic), potassium, dissolved silica, and dissolved silicon.
Flow (Figure 2) values showed consistent seasonal patterns, with the highest flows occurring during freshet in spring and early summer and the lowest flows occurring in late fall and winter. Flow monitoring should continue because of its importance in interpreting many water quality indicators.
Total alkalinity (Figure 3) and calcium (Figure 6) values showed that the river at this location was well buffered and had a low sensitivity to acid inputs at all times of the year.
Total aluminum (Figure 4) values showed fairly consistent peaks that exceeded the dissolved aluminum guidelines for aquatic life (0.05 - 0.1 mg/L) and for drinking water and recreation (0.2 mg/L), but remained well below the 5 mg/L total aluminum guideline for wildlife, livestock, and irrigation. However, total aluminum cannot be directly compared to the dissolved aluminum guidelines. The aluminum peaks were largely correlated with high flows and elevated non-filterable residue (Figure 33) during spring freshets. Therefore, most of the aluminum was likely in particulate form, and probably not biologically available. The dissolved aluminum fraction was suspected to be much lower. here appears to be a declining trend in peak total aluminum levels between 1993 and 1996, a trend partly explained by declining peak non-filterable residue values in 1994-96 (Figure 33). Both dissolved and total aluminum should be monitored in the future to allow for appropriate comparison to the guidelines.
Total organic carbon (Figure 8) values exceeded the 4 mg/L proposed guideline for drinking water between 1973 and 1975, but decreased to below the guideline since then, although the data are very sparse. Dissolved carbon should be measured in the future due to its role in the toxicity of metals and to evaluate the suitability of the water for drinking.
Dissolved chloride (Figure 9) values appear to have shown an increasing trend between 1991 and 1996. Levels have remained well below guidelines however, and are not of any current environmental concern, although a trend towards increasing concentration may signal some problem or contaminant in the environment, possibly road salt.
Total copper (Figure 12) measurements may have exceeded the 0.002 mg/L guideline for aquatic life, but the minimum detectable limits were too high to compare the total copper values to the guideline. The MDL will have to be lowered to at least one-tenth of the guideline to assess any environmental significance, and future monitoring should include total and dissolved copper to assess its biological availability.
Fecal coliforms (Figures
14 and 15) were measured by the multiple-tube
fermentation method from 1975 to 1989 (Figure
14) and by the membrane filtration method from 1988 to 1997 (Figure
15). E. coli, a more specific indicator of fecal contamination from
warm-blooded animals than fecal coliforms, was also measured during 1993-96
(Figure 13). The E. coli and fecal coliform levels were quite similar
during 1993-96. Fecal coliforms and E. coli were not measured frequently
enough (e.g., 5 or more times in 30 days) to permit rigorous comparison to the
objectives and guidelines. However, the data suggest that:
· the objective for raw drinking water receiving disinfection only (90th percentile of 10/100 mL) was probably not met.
· the guideline for raw drinking water receiving partial treatment and disinfection (90th percentile of 100/100 mL) was probably met.
· the objective for recreation and irrigation (geometric mean of 200/100 mL) was met.
Continued and more frequent monitoring (e.g., 5 or more times in 30 days) of fecal coliforms and/or E. coli should be done to evaluate the attainment of the objectives more rigorously, but it appears that reduction of the sources of fecal contamination is needed to meet the objective.
Hardness (Figure 16) values showed that the water was soft and always below the optimum range for drinking water (80 - 100 mg/L), but still quite acceptable for drinking. Hardness should continue to be monitored due to its influence on metal toxicity.
About 25% of the total iron (Figure 17) values were above the 0.3 mg/L drinking water (aesthetics) and aquatic life guideline. However, since most of the iron peaks coincided with turbidity or non-filterable residue peaks, the high iron content in the water was probably due to the iron content of the suspended sediment. Therefore, much of the iron was probably not in a bio-available form. Both dissolved and total iron should be monitored in the future.
Total molybdenum (Figure 20) met the lowest guideline for irrigation (0.01 mg/L) with the exception of one value of 0.02 mg/L in 1988, which may have been a false positive value close to the 0.01 mg/L detection limit.
Dissolved oxygen (Figure 27) values met the instantaneous minimum for all aquatic life stages with the exception of one value in 1974, but the instantaneous minimum for buried embryo/alevin life stages was often not met in 1974-76. It is not known if there were buried embryos or alevins in this reach of the South Thompson River at these times. No data have been collected since 1982.
pH (Figure 28) values remained within the upper and lower guidelines for drinking water and aquatic life between 1975 and 1996. We recommend that pH continue to be monitored due to its effect on organism physiology and its influence on other variables.
Total dissolved and total phosphorus (Figures 29 and 30) did not show any obvious trends and there are no guidelines for phosphorus in rivers. There was a statistically significant linear decreasing trend in total phosphorus between 1987 and 1995 (Regnier & Ryan, 1997), but the higher levels in 1996-97 appear to have nullified this trend. Peak total phosphorus values were well correlated with peak non-filterable residue values, indicating that much of the phosphorus was in a particulate form. This is confirmed by the total dissolved phosphorus values (Figure 29), which were significantly lower than total phosphorus values. Phosphorus is generally accepted as the limiting nutrient for algal growth in the Thompson River system (Nordin & Holmes, 1992), and, therefore it remains an important environmental indicator. Total and total dissolved phosphorus should continue to be monitored.
Filterable residue (FR) (i.e., dissolved solids) (Figure 32) levels were well below the upper limit for drinking water (aesthetics) and the irrigation guideline (500 mg/L), and did not show any obvious trend. Specific conductivity (Figure 11) is a more precise and cheaper variable to monitor and has a reasonably constant relationship to filterable residue. We recommend that conductivity be used as a surrogate for FR in future monitoring.
Non-filterable residue (NFR) (i.e., suspended solids or sediment) levels and Turbidity levels are shown in Figures 33 and 37, respectively. NFR levels were usually below the general fisheries guideline of 25 mg/L (Newcombe, 1986) during the non-freshet periods, but often exceeded it during the spring freshet between 1991 and 1998. The 50 NTU turbidity guideline for recreation was never exceeded, but the 1 NTU guideline for disinfected drinking water (health) was often exceeded and the 5 NTU guideline for disinfected drinking water (aesthetics) was occasionally exceeded. As the turbidity levels appear to be the result of human activities, such as forestry on Chase Creek and agriculture on other tributaries (Holmes, pc 1997), remediation in decreasing the sources and levels of non-filterable residues and turbidity is recommended. Because of the increasing trend in suspended solids during the 1987-98 period, mainly due to non-point sources of pollution such as agriculture, forestry and residential development, NFR and turbidity should continue to be monitored. Major erosion in tributary streams is another main cause of this increasing trend.
Water temperature (Figure 36) values usually remained below the 15 0C drinking water guideline (aesthetics) throughout the sampling period between 1974 and 1977, except during the summers. During the summers, the water temperature usually met or exceeded the lower limit for recreation (also 15 0C), indicating that the water was warm enough for swimming. Water temperature should again be monitored due to the impact it has on recreational activities, on drinking water aesthetics, on fisheries, on organism physiology, and on other water quality variables. Air temperature values should also be recorded.
Total zinc (Figure 38) values regularly exceeded the chronic effects guideline at 0.0075 mg/L and also the acute effects guideline at 0.033 mg/L during 1993-96. Many of these values were the product of suspected contamination due to preservative vial cap liner failures between 1993 and 1996. Unusually high zinc was found at three unrelated sites (S. Thompson, N. Thompson and Bonaparte rivers) during this time period, leading to the conclusion that it must have been due to artificial contamination (Brewer & Webber, 1997a and 1997b). Total and dissolved zinc should be measured in the future and the detection limit should be at least one tenth of the average guideline. It should be noted that current zinc guidelines are based on 30-day average results but there is insufficient reliable data here to meet the sample frequency criterion for both aquatic life guidelines.