The state of the water quality was assessed by comparing the values to Ministry of Environment, Lands and Parks' approved and working guidelines for Water Quality (Nagpal et al., 1998a,b). (Guidelines were formerly called criteria, and this older term has been used in many of the figures in this report.) Site-specific water quality objectives have not been set for Cusheon Lake. Any levels or trends in water quality that were deleterious to sensitive water uses, including drinking water, aquatic life and wildlife, recreation, irrigation, and livestock watering are noted below.
The water in Cusheon Lake was vertically mixed (no thermal stratification) between November and the end of April. A key time
for sampling is in the spring during this period of mixing. The objective of this monitoring was to assess water quality from year to year and to estimate the potential algal growth during the summer months.
Goddard (1976) identified five water uses for Cusheon Lake: domestic consumption, primary (e.g., swimming) and secondary (e.g., canoeing and angling) recreation, irrigation, aquatic life, and wildlife.
There were 35 domestic water licenses that may have been used as drinking water sources, and two local authority water works licenses on Cusheon Lake. The Beddis Water Works District holds the water works licenses.
Total phosphorus average values at spring overturn before thermal stratification (average of samples taken at different depths within the water column) are shown in Figure 3. They were above the upper guideline (0.015 mg/L) for protecting aquatic life in 6 of 14 years, and exceeded the guideline for protecting recreation and drinking water (0.010 mg/L) in 10 of 14 years during 1975-99. The spring overturn total phosphorus data were examined using non-parametric statistics, and weak evidence (i.e., 90% confidence level) of an increasing trend over 1975-99 was found (Regnier, 1999).
Ortho-phosphorus values (Figure 5) ranged from the minimum detectable limit (0.003 mg/L) to 0.238 mg/L. This high value was not included in this assessment as the sample may have contained bottom sediment. Seventy percent of the values were below the minimum detectable limit. Future monitoring should include total phosphorus and total dissolved phosphorus as a measure of bio-available phosphorus.
Ammonia-N values (Figure 6) were below the guideline (30-day average 1.85 mg/L) to protect aquatic life from toxicity. Generally, these values decreased between 1980 and 1995 with the exception of an increase in 1990.
Nitrate/nitrite-N values (Figure 8) were below the drinking water guideline (10 mg/L) and increased over time. The values ranged from the minimum detectable limit (0.02 mg/L) to 0.65 mg/L. The ammonia:nitrate ratio (Figure 10) decreased over time, with the exception of 1990, due to decreasing ammonia levels and increasing nitrate/nitrite levels.
Kjeldahl nitrogen (Figure 7) and nitrite/nitrate concentrations were added together to calculate total nitrogen (Figure 9), which was fairly constant over time. Total nitrogen and total phosphorus were used to calculate the Nitrogen:Phosphorus (N:P) ratio (Figure 11). This ratio indicates that phosphorus was the limiting factor for algae growth (N:P > 15). All ratios that were less than 15 occurred in October and November of 1974, 1976, 1980, and 1981. Future monitoring should include Kjeldahl nitrogen, nitrate/nitrite, and dissolved ammonia.
Total calcium values (Figure 12) show that the lake had a low sensitivity to acid inputs (the lake was well buffered to acid inputs).
Total organic carbon values (Figure 13) exceeded the raw drinking water guideline (4 mg/L) in 88% of the samples collected between 1974 and 1980. The water has the potential to form trihalomethanes in excess of the 0.1 mg/L drinking water guideline if disinfected with chlorine. Trihalomethane measurements should be included in future monitoring of chlorinated drinking water from the lake.
Inorganic carbon (Figure
14) and organic carbon (Figure 13)
were highly variable in 1980. Fluctuations in carbon values may be due to:
_ the demand for carbon dioxide for photosynthesis in relation to amount released through respiration occurring in the lake and sediments;
_ changes in the rate of decomposition of organic matter;
_ changes in the rate of microbial methane fermentation;
_ changes in the rate of nitrification of ammonia; and
_ changes in the rate of sulfide oxidation.
Dissolved chloride (Figure 15) values met all guidelines. Chloride values increased over time, which may indicate a disturbance within the watershed. Future monitoring should include dissolved chloride as a measure of changes in the rate that ions are released within the watershed, and as an indicator of possible disturbances within the watershed.
Chlorophyll a: Monthly samples were collected at several depths in 1980. The values ranged from 2.5 to 34 _g/L, with a mean of 13.7 _g/L. The guidelines for aquatic life (1-3.5 _g/L; Nordin 1985) and drinking water and recreation (2-2.5 _g/L; Nagpal et al. 1998a) were exceeded in most of the samples. Future monitoring should include chlorophyll a.
Fecal coliform values were collected between 1981 and 1995, and ranged from 2 to 240 /100 mL at the public beach near the boat ramp on Cusheon Lake (Table 2). The values from the beach site may not be representative of values elsewhere in the lake. The Capital Health Region determined that the public beach was suitable for bathing between 1981 and 1995. The Capital Health Region will continue to measure fecal coliforms at the beach.
There were 35 domestic water licenses that may have been used as drinking water sources, and two local authority water works licenses held by the Beddis Water Works District. The Ministry of Health recommends that all surface waters in the province receive disinfection, as a minimum, before being used for drinking. Raw water fecal coliform values must not exceed the 90th percentile guideline of 100 /100 mL for partially treated and disinfected drinking water, and 10 /100 mL for drinking water receiving only disinfection. Fecal coliforms monitoring was not done near water intakes, nor at a sufficient frequency to permit comparison to drinking water guidelines. Future monitoring should include fecal coliform measurements near drinking water intakes to evaluate the suitability of Cusheon Lake water as a raw drinking water source.
True colour values (Figure
16) exceeded the guideline (15 units) for drinking water aesthetics in 33%
of the samples collected from Cusheon Lake. Future monitoring should include
Extinction depth values (Figure 17) ranged from 1 to 5.4 m during 1974-94. One value measured in October 1980 did not meet the guideline (>1.2 m) for swimming, and may indicate that the guideline was not met in the summer months when swimming would most likely have occurred. Future monitoring should include extinction depth as an indicator of water clarity and changes in the amount of particulate and dissolved matter in the water column.
Total iron values (Figure 18) exceeded the guideline (0.3 mg/L) for aquatic life and drinking water (aesthetics) in two samples collected in 1974. Since then, the guideline has been met.
Total manganese values (Figure 20) exceeded the guideline (0.05 mg/L) for drinking water (aesthetics) in two samples in 1993 and one sample in 1994.
Dissolved oxygen values (Figure 21) did not meet the guideline (8 mg/L) for protecting adult and juvenile salmonids from production impairment in 29% of the samples collected during 1974-94. Dissolved oxygen values that did not meet this guideline were collected between October and December, in samples collected at depth, and in one value collected in April 1994. The guideline (5 mg/L) for protecting adult and juvenile salmonids from moderate production impairment was not met in 2% of the samples during 1974-94. This guideline was not met in samples collected in October and December 1980 at depth. Future monitoring should include dissolved oxygen.
pH values (Figure 22) met all guidelines, ranging between 6.7 and 7.7. Future monitoring should include pH.
Total residue (i.e., dissolved plus suspended solids) values, collected between 1980 and 1994, ranged from 72 mg/L to 106 mg/L (Figure 23). There are no guidelines for total residue. The guideline for suspended solids could not be used because there were insufficient suspended solids (non-filterable residue) data.
Dissolved silica values (Figure 24) ranged from 5 to 11.6 mg/L in samples collected between 1980 and 1995. The decrease in dissolved silica values in 1994 may be due to an increase in the diatom population. Dissolved silica was not a limiting nutrient (i.e., values were greater than 0.5 mg/L) for diatom growth in Cusheon Lake (Wetzel, 1975).
Dissolved sodium values (Figure 25) increased between 1975 and 1993 in Cusheon Lake in the same manner as chloride, but met all guidelines. Future monitoring should include dissolved sodium as a measure of changes in the rate that ions are released within the watershed and as an indicator of possible disturbances within the watershed.
Specific conductivity (Figure 28) can be used to indicate dissolved solids concentrations. The values ranged from 58 to 134 _S/cm, and were below all guidelines. Specific conductivity values increased over time. Future monitoring should include specific conductivity as a measure of changes in the rate that ions are released within the watershed, and as an indicator of possible disturbances within the watershed.
Water temperature (Figure 27) exceeded the drinking water (aesthetics) guideline (15 o C) at the deep station in Cusheon Lake in October 1980. The values were collected from the surface and to a depth of 6 m, and imply that the guideline may also have been exceeded during the summer. Future monitoring should include water temperature.
28) was measured for five years during 1974-95. The 5 NTU aesthetics objective
for drinking water (with disinfection only) was met except for a few values
in 1980. The drinking water health guideline (1 NTU) was exceeded in 80% of
the samples. All values collected in 1994-95 met the turbidity guideline and
objective. Increased turbidity may be caused by:
_ natural erosion within the Cusheon Lake basin,
_ changes in land-based activities adjacent to the lake (e.g., forestry, agriculture, urbanization), or
_ an increase in the amount of biological material (e.g., plankton) in the water column.
The turbidity levels in the Cusheon Lake were such that treatment to remove it would have been needed prior to drinking. Future monitoring should include turbidity to evaluate the suitability of the lake water as a drinking water supply.