Canada - British Columbia Water Quality Monitoring Agreement
Water Quality Section
Water Management Branch
Ministry of Environment, Lands and Parks
April, 1996
Langford lake is located on southern Vancouver Island near Victoria, B.C. The watershed for this small lake is 3.3 km².
This report assesses 16 years of water quality data and made the following conclusions:
We recommend monitoring:
This monitoring program could be implemented by a Langford Lake stewardship group with assistance from the Ministry of Environment, Lands and Parks.
The monitoring program is being implemented by the Capital Regional District's Health Protection and Environmental Program Division. In future, local interest groups (e.g., Langford Lake stewardship group, Municipality of Langford) could assist with this ongoing monitoring.
Figure 1 Langford Lake Watershed
Approximate
Scale 1:50,000
Table of Contents
Executive Summary
Acknowledgements
Introduction
Quality Assurance
State of the Water Quality
Conclusions - State of Water Quality
Recommendations
for Water Quality Management
List of Figures
Figure 1 Langford Lake Watershed
Figure
2 Bathymetric map of Langford Lake
Figure 3 Total
phosphorus (average in the water column before stratification) from Langford
Lake
Figure 4 Total phosphorus from Langford Lake
Figure 5 Total dissolved phosphorus from Langford Lake
Figure 6 Dissolved ammonia from Langford Lake
Figure 7 Nitrate/Nitrite from Langford Lake
Figure
8 Kjeldahl nitrogen from Langford Lake
Figure 9 N:P
ratio from Langford Lake
Figure 10 Dissolved
ammonia:nitrate ratio from Langford Lake
Figure 11
Total residues from Langford Lake
Figure 12 Specific
conductivity from Langford Lake
Figure 13 Total
manganese from Langford Lake
Figure 14 Dissolved
silica from Langford Lake
Figure 15 pH from Langford
Lake
List of Tables
Table 1 Summary of water quality data from Langford Lake
(SEAM sites 1100844 and 1100953)
Table 2 Summary of
Capital Regional District's Health Protection and Environmental Division's
Bacteriological data from Langford Lake (on the north side of the lake off of
Goldstream Road)
Author
Holms, G. Bruce B.Sc. Research Officer. Water Quality Branch, Environmental Protection Department, Victoria, B.C.
Drafts of this report were sent to Lloyd Erickson and John Deniseger, Environmental Protection in Nanaimo, Gary Gibson, Capital Regional District, Barry Boettger, Public Health Protection, Rick Nordin and Larry Pommen, Water Quality. Valuable comments were provided and incorporated into this report.
Langford Lake is located on southern Vancouver Island near Victoria, B.C. The watershed for this small lake is 3.3 km². The surface area of the lake is 60 ha and has an average flushing rate of once in 3.3 years (Nordin and McKean, 1988). The lake has a maximum depth of 15 m and a mean depth of 6.4 m (Figure 2). There is one inflow stream and one outlet stream from Langford lake. The outlet stream discharges into Saanich Inlet via Goldstream River.
The Ministry of Environment, Lands and Parks monitored the water quality at the deepest point (15 m) of the basin between 1973 and 1995. The data are stored on the provincial data base, SEAM, under station numbers 1100944 and 1100953. The two purposes for monitoring the water quality of Langford lake are to identify:
The Capital Regional District's Health Protection and Environmental Division collected fecal coliform samples from one bathing beach on the north side of the lake off Goldstream Road (Figure 2). Weekly sampling begins in April each year and continues through the bathing season, ending in September. Fecal coliform results from five samples collected within a 30-day period are used to establish a geometric mean at the beginning of the season. A beach advisory notice, warning of the potential for increased risk to bathers' health, is considered for posting if the geometric mean exceeds 200 fecal coliforms/100 mL over a 30-day period. More intense sampling may occur if the results of a single sample exceeds 400 fecal coliforms/100 mL.
This report assesses 22 years of water quality data. These data consist of:
The water quality data are plotted in Figures 3 to 15 and summarized in Tables 1 and 2.
The box plots, in Figures 3 to 15, represent the variability of water quality indicators collected at the surface, mid depth, and near the bottom of the lake. Each plot is comprised of a rectangle with the top portraying the upper quartile (75th percentile of the data series, Q(0.75)), the bottom portraying the lower portion (25th percentile of the data series, Q(0.25)), and a horizontal line within the rectangle portraying the median. Vertical lines extend from the ends of the rectangle to the adjacent values, also known as "whiskers", and are defined by:
Values that fall outside the range of the adjacent values are defined as "outside values" and are plotted as asterisks (*). Values are defined as "far outside values" if they are located outside the outer range which is defined as the upper quartile plus 3 X IQR or the lower quartile minus 3 X IQR. These values are plotted as empty circles (O).
Trends in water quality data collected at different depths and at different frequencies over time are assessed by comparing yearly changes in median values in conjunction with the size of sample variability. The size of sample variability is represented in the box plots by the rectangle, whiskers, and the two types of outliers. A change is observed when the median values and sample variability do not overlap.
Figure 2 Bathymetric map of Langford Lake
Adapted
from Nordin and McKean (1988)
Scale 1:13,000
The water quality plots were reviewed. Total residue (i.e. dissolved and suspended solids) from Langford Lake increased in 1994 (Figure 11). Dissolved residues did not increase in 1994 which indicates that the increase in total residues values during this period may be outliers or questionable values. The effect of suspended solids (non-filterable residues) values on total residues values in 1994 could not be determined because suspended solids values were not collected.
The state of the water quality is assessed by comparing the values to any site-specific water quality objectives or to Ministry of Environment, Lands and Parks' Approved and Working Criteria for Water Quality (Nagpal et al., 1995) if objectives have not been set. Any levels or trends in water quality that are deleterious to sensitive water uses are noted.
Nordin and McKean (1988) identified two water uses (water-based recreation and fisheries) for Langford lake. These uses were threatened by excessive phosphorus loading from agricultural runoff and phosphorus being generated from the sediments in the lake. An aerator was installed in 1984 to provide oxygen to the deep waters of the lake and to reduce the amount of phosphorus released by the lake sediments.
The water in Langford Lake is vertically mixed (no thermal stratification) between November and the end of April. A key time for sampling is late during this period of mixing. The objective of this monitoring is to assess water quality from year to year and to estimate the potential algal growth during the summer months in Langford Lake.
Total phosphorus (Figure 3) values before thermal stratification, average of samples taken at different depths within the water column, were outside limits (0.005-0.015 mg/L) for protecting aquatic life between 1973 and 1988. These values were within these limits between 1989 and 1995. The criterion (0.01 mg/L) for recreational use was exceeded between 1973 and 1992. Total phosphorus values, before thermal stratification, met this criterion between 1993 and 1995.
Ortho-phosphorus values, with the exception of an increase in 1985, approximated the minimum detectable limit (0.003 mg/L). Total phosphorus (Figure 4) and Total dissolved phosphorus (Figure 5) values decreased over time. This decrease of phosphorus in the water column may be attributed to several factors including:
Nitrogen, dissolved ammonia (Figure 6) and nitrate/nitrite (Figure 7) were below all criteria. Kjeldahl nitrogen (Figure 8) and dissolved ammonia values were less variable after 1984 and decreased over time. Kjeldahl nitrogen and nitrite/nitrate concentrations are added together to represent total nitrogen in the lake. These concentrations are used to calculate the N:P ratio.
Nordin and McKean (1988) reported an average N:P ratio of 26:1 in 1983/1984. This ratio has approximately doubled between 1985 and 1995 (Figure 9). Phosphorus is the limiting nutrient for algal in Langford Lake (N:P > 15:1). The dissolved ammonia:nitrate ratio (Figure 10) decreased over time. The trends in the ratios indicate that there are changes occurring in the lake systems (e.g. land use, biological activity) which affect water quality.
Fecal coliform samples were collected by the Capital Regional District's Health Protection and Environmental Division at a bathing beach on the north side of the lake off Goldstream Road. Samples were collected between 1980 and 1995 (Table 2). These values ranged between 1 MPN/100 mL and 1100 MPN/100 mL. Fecal coliform values from this beach may not be similar to values collected elsewhere in the lake. Resident waterfowl populations make these areas unique and may cause fecal coliform values to be higher than at other sites in the lake. The bathing beach on the north side of Langford Lake was suitable for bathing between 1980 and 1995 (Table 2).
Total residue (i.e. dissolved and suspended solids) increased in 1994 (Figure 11). Dissolved residues did not increase in 1994 which indicates that the increase in total residues values during this period may be outliers or questionable values. There are no criteria for total residues. Dissolved solids (filterable residues) and suspended solids (non-filterable residues) values were collected in 1984, and 1993. There was insufficient suspended solids data to apply the criterion for the protection of aquatic life. Specific conductivity (µS/cm) (Figure 12) can be used to indicate dissolved solid concentrations. These values ranged between 164 µS/cm and 188 µS/cm. Specific conductivity values increased over time but were below all criteria.
Total calcium shows that Langford lake has a low sensitivity to acid inputs (the lake is highly buffered to acidic inputs). These concentrations ranged from 18 mg/L to 23.5 mg/L between 1984 and 1995.
Total manganese: (Figure 13) 13% of the values exceeded the lower criterion (0.10 mg/L) for protecting aquatic life. These 3 values occurred in 1984 and 1985. Total manganese values were at or near the minimum detection limit (0.01 mg/L) between 1985 and 1995. The upper criterion (1.0 mg/L) was not exceeded.
Iron values were below all criteria.
Chloride values were below all criteria.
Dissolved silica (Figure 14) values increased and decreased between 1983 and 1995. These changes in dissolved silica values may be attributed to the activity of the diatom population in the lake. Dissolved silica is not the limiting nutrient (< 0.5 mg/L) for diatom growth in Langford Lake (Wetzel, 1975).
pH (Figure 15) values met all criteria. These values ranged between 7.1 and 8.3.
Dissolved oxygen, extinction depth, and water temperature were measured in 1994. Dissolved oxygen and water temperature values met all criteria and were similar to those reported by Nordin and McKean (1988). The extinction depth value was similar to those reported by Nordin and McKean (1988). There are not criteria for extinction depth.
Conclusions - State of Water Quality
Recommendations for Water Quality Management
A destratification aeration system was installed in 1984. The aerator operates between April and October. There are no other apparent water quality remediation measures needed at this time.
We recommend that sampling at the surface and at depth during spring overturn and between June and September at SEAM site 1100994. The focus of this monitoring will be to identify changes in water quality attributed to activities within the watershed such as urbanization, changes in nonpoint discharge, biological activity, and lake aeration. This monitoring program would include the following water quality indicators:
This monitoring program could be implemented by a Langford Lake stewardship group with assistance from the Ministry of Environment, Lands and Parks.
We recommend that fecal coliform sampling continue at the bathing beach on the north side of Langford Lake. The monitoring program is being implemented by the Capital Regional District's Health Protection and Environmental Division. In future, local interest groups (e.g., Langford Lake stewardship group, Municipality of Langford) could assist with this ongoing monitoring.
Figure 3 Total phosphorus (average in the water column before stratification) from Langford Lake
Figure 4 Total phosphorus from Langford Lake
Figure 5 Total dissolved phosphorus from Langford Lake
Figure 6 Dissolved ammonia from Langford Lake
Figure 7 Nitrate/Nitrite from Langford Lake
Figure 8 Kjeldahl nitrogen from Langford Lake
Figure 9 N:P ratio from Langford Lake
Figure 10 Dissolved ammonia:nitrate ratio from Langford Lake
Figure 11 Total residues from Langford Lake
Figure 12 Specific conductivity from Langford Lake
Figure 13 Total manganese from Langford Lake
Figure 14 Dissolved silica from Langford Lake
Figure 15 pH from Langford Lake
Table 1 Summary of water quality data from Langford Lake (SEAM sites 1100944 and 1100953)
|
Water Quality |
Average |
Std Dev |
Number of |
Maximum |
Minimum |
|
SPRING OVERTURN |
. |
. |
. |
. |
. |
|
Water Clarity and Colour |
. |
. |
. |
. |
. |
|
Turbidity (NTU) |
0.76 |
0.218 |
13 |
1.1 |
0.4 |
|
Colour, true (TCU) |
6.8 |
2.52 |
11 |
10 |
5 |
|
Residues, nonfilterable (mg/L) |
2.4 |
1.12 |
11 |
L 4 |
1 |
|
Extinction depth (m) |
3.95 |
0.532 |
4 |
4.5 |
3.4 |
|
General Ions |
. |
. |
. |
. |
. |
|
pH (pH units) |
7.68 |
0.298 |
26 |
8.3 |
7.1 |
|
Residues, filterable (mg/L) |
106.7 |
3.06 |
3 |
110 |
104 |
|
Residues, total (mg/L) |
123.2 |
36.52 |
18 |
232 |
100 |
|
Specific conductivity (µS/cm) |
171.7 |
7.13 |
24 |
188 |
164 |
|
Calcium, total (mg/L) |
20.63 |
1.535 |
21 |
23.5 |
18.1 |
|
Chloride, dissolved (mg/L) |
10.93 |
0.427 |
12 |
11.4 |
10.1 |
|
Magnesium, total (mg/L) |
4.264 |
0.4282 |
21 |
5.05 |
3.55 |
|
Silica, dissolved (mg/L) |
3.48 |
2.455 |
15 |
7.2 |
0.6 |
|
Sulphate, dissolved (mg/L) |
16.18 |
8.523 |
4 |
24.9 |
7.9 |
|
Temperature, water (° C) |
9.53 |
2.275 |
57 |
19.5 |
5.9 |
|
Nutrients |
. |
. |
. |
. |
. |
|
Carbon, total organic (mg/L) |
2.5 |
1.65 |
14 |
6 |
L1 |
|
Carbon, total inorganic (mg/L) |
16.3 |
2.23 |
14 |
20 |
11 |
|
Nitrogen, total (mg/L) |
0.655 |
0.1751 |
27 |
1.21 |
0.35 |
|
Nitrogen, ammonia (mg/L) |
0.066 |
0.1115 |
57 |
0.675 |
L 0.005 |
|
Nitrogen, Kjeldahl (mg/L) |
0.421 |
0.1541 |
57 |
1.17 |
0.24 |
|
Nitrogen, organic (mg/L) |
0.358 |
0.0535 |
29 |
0.5 |
0.28 |
|
Nitrogen, nitrate+nitrite (mg/L) |
0.146 |
0.111 |
59 |
0.5 |
L 0.02 |
|
Phosphorus, total (mg/L) |
0.024 |
0.0200 |
62 |
0.151 |
0.006 |
|
Phosphorus, ortho (mg/L) |
0.007 |
0.0137 |
45 |
0.089 |
L 0.003 |
|
Phosphorus, total dissolved (mg/L) |
0.013 |
0.0125 |
56 |
0.097 |
L 0.003 |
|
Oxygen, dissolved (mg/L) |
11.20 |
1.250 |
54 |
13.7 |
7.5 |
|
Chlorophyll a (mg/L) |
0.006 |
0.0009 |
6 |
0.0063 |
0.004 |
|
Metals |
. |
. |
. |
. |
. |
|
Aluminum, total (mg/L) |
. |
. |
8 |
L 0.02 |
L 0.015 |
|
Antimony, total (mg/L) |
. |
. |
9 |
L 0.02 |
L 0.015 |
|
Arsenic, total (mg/L) |
. |
. |
21 |
L 0.25 |
L 0.04 |
|
Boron, total (mg/L) |
. |
. |
8 |
L 0.04 |
0.008 |
|
Barium, total (mg/L) |
. |
. |
8 |
L 0.007 |
L 0.004 |
|
Beryllium, total (mg/L) |
. |
. |
8 |
L 0.001 |
L 0.001 |
|
Bismuth, total (mg/L) |
. |
. |
8 |
L 0.02 |
L 0.02 |
|
Cadmium, total (mg/L) |
. |
. |
21 |
L 0.01 |
L 0.002 |
|
Cobalt, total (mg/L) |
. |
. |
21 |
L 0.1 |
L 0.003 |
|
Chromium, total (mg/L) |
. |
. |
21 |
L 0.05 |
L 0.002 |
|
Copper, total (mg/L) |
. |
. |
21 |
0.012 |
L 0.001 |
|
Iron, total (mg/L) |
0.05 |
0.057 |
21 |
0.26 |
0.01 |
|
Lead, total (mg/L) |
. |
. |
21 |
L 0.1 |
L 0.02 |
|
Manganese, total (mg/L) |
0.06 |
0.118 |
21 |
0.55 |
0.009 |
|
Molybdenum, total (mg/L) |
. |
. |
21 |
L 0.01 |
L 0.004 |
|
Nickel, total (mg/L) |
. |
. |
21 |
L 0.05 |
L 0.008 |
|
Selenium, total (mg/L) |
. |
. |
8 |
L 0.03 |
L 0.03 |
|
Sodium, dissolved (mg/L) |
7.5 |
0.34 |
8 |
8 |
6.9 |
|
Silicon, total (mg/L) |
2.02 |
0.772 |
8 |
2.84 |
0.8 |
|
Silver, total (mg/L) |
. |
. |
8 |
L 0.03 |
L 0.01 |
|
Strontium, total (mg/L) |
0.056 |
0.007 |
8 |
0.064 |
0.047 |
|
Tin, total (mg/L) |
. |
. |
8 |
L 0.02 |
L 0.02 |
|
Zinc, total (mg/L) |
. |
. |
8 |
L 0.003 |
L 0.003 |
Note: L = less than
|
Year |
Maximum |
Minimum |
Geometric |
Number of |
|
1980 |
35 |
5 |
13.48 |
8 |
|
1981 |
38 |
24 |
26.92 |
4 |
|
1982 |
700 |
L 3 |
20.98 |
8 |
|
1983 |
8 |
5 |
5.44 |
10 |
|
1984 |
24 |
7 |
8.35 |
11 |
|
1985 |
43 |
28 |
33.93 |
14 |
|
1986 |
240 |
3 |
10.47 |
8 |
|
1988 |
1100 |
3 |
14.9 |
18 |
|
1990 |
17 |
11 |
14.03 |
5 |
|
1991 |
29 |
5 |
10.16 |
12 |
|
1992 |
15 |
4 |
6.87 |
13 |
|
1993 |
4 |
1 |
1.97 |
12 |
|
1994 |
6 |
2 |
2.80 |
13 |
|
1995 |
3 |
1 |
1.9 |
10 |
Note: L = less than
Nagpal, N.K., L.W. Pommen, and L.G. Swain (1995). Approved and Working Criteria for Water Quality. Ministry of Environment, Lands and Parks. Environmental Protection Department, Water Quality Branch, Victoria, BC.
Nordin, Richard N. and C.J.P. McKean (1988) Destratification-Aeration of Langford Lake: Physical, Chemical and Biological Responses. Water Quality Unit, Resource Quality Section, Water Management Branch Ministry of Environment, Victoria B.C.
McKean, C.J.P. and N. Munteanu (1982) An Assessment of the water quality of Langford Lake with proposals for the possible solutions to its eutrophication problem. Report submitted to the Langford Lake Improvement District and the Capital Regional District Planning Department. Victoria B.C.
|
Last updated: August 8, 2001