Water Quality Assessment and Objectives for Comox Lake TECHNICAL REPORT

Phytoplankton was mentioned 33 times in the original document, and algae 14 times. I copied all the sections that mentioned these two terms so readers could read a summary of the report and certain sections highlighted. I found the document very helpful and bolded the text that outlined the tests and italicized the text that defined a baseline to identify future problems.

My main concern with any report on cyanobacteria that sets guidelines and recommendations are how inconsistent cyanobactera or blue-green algae are and the inability of testing to show consistent results. Click here to learn more about phytoplankton and algae.

Click here to read the full report or an excerpt below.

 

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5.0 STUDY DETAILS

Three water quality monitoring sites were established in Comox Lake: one in the inlet basin (Site E259497); one in the main basin (Site E259498), and one in the outlet basin (Site E259499) (see Figure 3). All sites were located mid-lake, in the deepest part of the basin. Sampling at the three lake basin sites was conducted in March and November, while the water column was mixed, and during May/June and August, when the water column was thermally stratified. To represent the worst case scenario, bacteriological samples were collected weekly for 5 consecutive weeks during summer low flow (August/September) and fall flush (October/November) periods, at seven near-shoreline locations in the inlet and outlet basins (Table 3 and Figure 3). The bacteriological monitoring sites were selected in areas closest to cabins and campgrounds as well as areas habituated by waterfowl, as these are the areas likely to have the highest coliform concentrations. All samples were collected according to Resource Inventory Standards Committee (RISC) standards (Cavanagh et al., 1994).

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Water quality samples were collected from March 2005 to March 2008 in Comox Lake. Grab samples were taken at three depths in the water column (0.5 m, 10 m and 1 m from the bottom) for the three deep stations and at the surface for the perimeter sites. Surface samples were collected by hand and water column samples were collected using a Van Dorn bottle. The deep station samples were analyzed for the following parameters:

 Physical: pH, true color, specific conductivity, turbidity, non-filterable residue

 Carbon: total inorganic carbon, total organic carbon

 Nutrients: total phosphorus, nitrate, nitrite, ammonia, total Kjeldahl N

 Total and dissolved metals concentrations

Water chemistry analyses were conducted by Maxxam Analytics Inc. in Burnaby, British Columbia.

Depth profiles were conducted in the field for dissolved oxygen, water temperature, oxidation-reduction potential (ORP), pH and conductivity using a Hydrolab Surveyor 4. Measurements were made every metre between the surface and 10 m depth, and then, on most occasions, every five metres until the final sample was collected just above the bottom (as deep as 55 m at the inlet basin site, 125 m in the main basin, and 35 m in the outlet basin). Water clarity was measured at the deep stations on each sampling day using a Secchi disc, which is a 20 cm diameter circular plastic disk whose surface is divided into four quadrants alternating in colour between black and white. The disk is lowered into the water with a rope, and the depth at which it disappears from sight is termed the extinction, or Secchi, depth.

There was a concern that the field pH probe was not functioning properly for some of the sampling dates, as very low values (near 6.0 pH units) were occasionally measured at each of the sites. These values were considerably lower than the laboratory values reported for the same day, and therefore only the more reliable laboratory data were used in the report.

Microbiological samples were collected at the surface only for all seven near-shore sites and analyzed for fecal coliforms and E. coli. Bacteriological analyses were conducted by Cantest Laboratories in Burnaby, British Columbia. Geometric means were calculated using data from a minimum of 5 weekly samples in 30 consecutive days for each site.

Phytoplankton and chlorophyll a samples were collected by taking one litre grab samples at a depth of 0.5 m at the seep stations. Chlorophyll a samples were field filtered using 0.45 µm filter paper and then analyzed at the laboratory (Maxxam Analytics Inc.). Phytoplankton samples were preserved with Lugol’s solution and shipped on ice to the laboratory for analyses. Zooplankton samples were collected to determine community composition and densities using a 10 m vertical tow in a Wisconsin-style net with a mouth area of 0.07 m2 , a net opening diameter of 0.3 m and a mesh size of 80 μm. Zooplankton samples were preserved with formalin and shipped on ice to the lab for identification and enumeration. Phytoplankton and zooplankton taxonomy was done by Fraser Environmental Services, in Surrey, British Columbia. All biological samples were collected following Ministry of Environment approved methods (Cavanagh et al., 1997).

6.1 LIMNOLOGICAL CHARACTERISTICS

Limnological characteristics are generally considered those related to the dynamics of the lake, including whether thermal or chemical stratification occurs. Thermal stratification is driven by the fact that water is at its most dense at about 4°C. In most lakes in BC, surface waters cool in the fall and as temperatures reach 4°C, the denser water settles to the bottom of the lake. Similarly, in the spring, colder water (near 0°C) gradually warms to 4°C, at which point it begins to settle to the bottom. These temperature changes, usually assisted by spring and fall wind-storms, result in a mixing of the water column.

During the summer (as well as in the winter, if there is ice cover), surface waters are considerably less dense than the colder water at the bottom. These differences in density provide resistance to mixing, and in the absence of continuous winds or strong water currents, the water column can become thermally stratified. This results in a division of the water column into three sections – the epilimnion or top layer, the metalimnion or middle layer (which contains the thermocline, the plane of maximum rate of decrease of temperature with respect to depth (Wetzel 1982)) and the hypolimnion, or bottom layer. This can have various consequences to water chemistry because, in a strongly stratified lake, water in the hypolimnion does not mix with surface waters. If the depth of the hypolimnion is greater than the euphotic depth (the maximum depth at which photosynthesis meets or exceeds respiration), dissolved oxygen levels are not replenished because there is no exchange with the atmosphere (as there is in the epilimnion), or production of oxygen through photosynthesis. In some lakes, oxygen concentrations decrease sufficiently to impact fish species.

Dissolved oxygen levels in the hypolimnion can become depleted due to the decomposition of algae that dies and sinks to the bottom. As well, if waters near the sediment become anoxic, chemical reactions can result that release nutrients and other chemical parameters from sediments back into the water column. This explanation of stratification is very simplified and there are a number of different factors that affect stratification and water chemistry; but it gives an overview of typical lake dynamics in the temperate zone.

6.1.2 Dissolved Oxygen

Dissolved oxygen (DO) levels are important for the survival of aquatic organisms, especially species sensitive to low oxygen levels such as salmonids. Oxygen becomes dissolved in water on the surface of lakes as a result of diffusion from the atmosphere, as well as from photosynthetic activity from plants and algae. When deeper waters no longer mix with surface waters, due to stratification, concentrations of DO can decrease. This occurs as a result of decomposition of organic materials, especially in eutrophic lakes (i.e., lakes with high levels of nutrients and therefore high biological productivity). If the euphotic zone (the zone where light penetration is sufficient to allow photosynthesis) lies above the thermocline, no photosynthesis occurs in deeper waters, and therefore oxygen depletion from decomposition occurs. The guideline for the minimum instantaneous DO concentration for aquatic life is 5 mg/L (BC Ministry of Environment, 1997).

Dissolved oxygen concentrations were consistently at or near saturation levels in each of the three basins. As DO levels were similar for all three basins only the main basin data was used to illustrate seasonal differences (Figure 8). In general, when the lake was thermally stratified, concentrations increased with depth, as water temperatures decreased (resulting in increased oxygen solubility). On occasion, especially during the fall months (when algae would be senescing), DO concentrations near the bottom of the inlet basin decreased slightly, with a minimum recorded value of 6.1 mg/L. This is likely due to decomposition of organic material that grew over the course of the summer. However, at shallower depths (more than 5 m above the substrate), concentrations consistently exceeded 8 mg/L, while all values measured in the main and outlet basins were above 8.5 mg/L. Even when the lake was strongly stratified, oxygen concentrations in the deeper portion of the lake remained high, suggesting that there is low biological productivity and therefore low oxygen demand. As such, it does not appear that DO concentrations are a concern in Comox Lake at this time. However if human activities such as forestry, recreation or land development increase in the watershed, there is the potential for increased nutrient loading and a resulting increase in lake productivity. The establishment of a water quality objective for DO would serve as an early warning sign for impact from future activities. The objective is that DO concentrations measured at any depth in each basin, should be ≥ 5 mg/L during the summer months.

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6.2.5 Nutrients (Nitrate, Nitrite and Phosphorus)

The concentrations of nitrogen (including nitrate and nitrite) and phosphorus are important parameters, since they tend to be the limiting nutrients in biological systems. Productivity is therefore directly proportional to the availability of these parameters. Nitrogen is usually the limiting nutrient in terrestrial systems, while phosphorus tends to be the limiting factor in freshwater aquatic systems. Lakes are typically sampled during the spring and/or fall because this is when turn-over, or vertical mixing of the water column, occurs. Generally, spring turn-over is when the highest concentrations of phosphorus are found. Later in the season, phosphorus is assimilated by micro-organisms such as phytoplankton, and is therefore found in lower quantities in solution. However, if lakes are undergoing internal nutrient loading, typically eutrophic lakes, then the highest concentrations of phosphorus may be found in the fall. In watersheds where drinking water is a priority, it is desirable that nutrient levels remain low to avoid algal blooms and foul tasting water. Similarly, to protect aquatic life, nutrient levels should not be too high or the resulting plant and algal growth can deplete oxygen levels when it dies and begins to decompose, as well as during periods of low productivity when plants consume oxygen (i.e., at night and during the winter under ice cover). Conversely, you do need a certain amount of nutrients in a lake system to maintain productivity (i.e. 5 – 15 µg/L total phosphorus for aquatic life).

The guideline for the maximum concentration for nitrate for drinking water, recreation and aesthetics is 10 mg/L as nitrogen. For the protection of freshwater aquatic life, the nitrate guidelines are a maximum concentration of 31.3 mg/L and an average concentration of 3 mg/L. Nitrite concentrations are dependent on chloride; in low chloride waters (i.e., less than 2 mg/L) the maximum concentration of nitrite is 0.06 mg/L and the average concentration is 0.02 mg/L. Allowable concentrations of nitrite increase with ambient concentrations of chloride (Meays, 2009).

Nitrogen concentrations were generally measured in terms of dissolved nitrite (NO2) + dissolved nitrate (NO3). Dissolved nitrate + nitrite concentrations ranged from 0.007 mg/L to 0.067 mg/L, with an average of 0.034 mg/L in Comox Lake at the inlet site.

Values were similar in the main basin, ranging from < 0.002 mg/L to 0.072 mg/L and an average of 0.037 mg/L, as well as the outlet basin (0.006 mg/L to 0.060 mg/L, with an average of 0.033 mg/L). The combined concentrations of nitrate and nitrite were well below the existing aquatic life guidelines.

In lakes, a well defined relationship exists between total phosphorus concentrations (measured at spring overturn), and the amount of algal biomass (measured as chlorophyll a) produced in a lake during the growing season. Since phosphorus is much less difficult to measure than algal biomass, and can be easily correlated to other important lake characteristics such as water clarity and hypolimnetic dissolved oxygen, the guideline for nutrients and algae in lakes is presented in terms of total phosphorus concentrations (Nordin, 2001). The guideline for maximum total phosphorus concentrations in B.C. lakes is 10 µg/L to protect drinking water and recreation, and a range of 5 to 15 µg/L to protect aquatic life when salmonids are the dominant species (Nordin, 1985). Almost half (44 of 90) of all samples from the three sites analyzed for total phosphorus had concentrations below the detection limit (2 µg/L). The maximum values measured at the three sites ranged from 6 µg/L at both the main and outlet sites to 10 µg/L at the inlet site. The high phosphorus value at the inlet basin was only observed on one occasion (August 2006 at the bottom depth), otherwise the next highest value was 7 µg/L. As the slightly higher concentration of phosphorus in the inlet basin was only observed on one occasion, it is likely due to contributions/contamination of sediment particles that may have been stirred up in the bottom at the time of sampling. This is supported by the presence of some slightly higher total metal results at this site from the same sample date and depth.

Concentrations of nitrogen and phosphorus are generally low in Comox Lake. However, to protect fundamental water quality and to ensure a balance of nature, human use and recreational values, an objective is recommended for total phosphorus in Comox Lake. The objective is that the average concentration of total phosphorus during spring overturn not exceed 6 µg/L. Average spring overturn phosphorus levels at the three sites were well below the phosphorus guideline over the course of the study, and therefore should continue to be met, as long as significant new sources of nutrients do not emerge. This objective will act as a red flag should phosphorus values increase and will identify that further investigation is warranted.

6.3.2 Phytoplankton

Phytoplankton populations can have significant impacts on water quality, and may give an indication of contaminant and nutrient levels in a lake. Algal blooms resulting from elevated nutrient levels can impair water quality in a number of ways. Algae can clog water filters and can impact taste and odour to drinking water, requiring expensive treatments to remove algal particles. If algae are not removed prior to chlorination, byproducts can be formed that are potentially carcinogenic (Nordin, 1985). Some species of phytoplankton (specifically “blue-green algae”or cyanobacteria) also contain toxins. Allergic reactions to algae in drinking water, or from exposure to algae while swimming, are also common. Aesthetically, algal blooms reduce water clarity and can result in an unpleasant “scum” on the surface of the water, as well as give the water a strong odour.

Changes in algal populations can also affect other biota in the lake, including the zooplankton populations that feed on the algae and fish that feed either on algae, zooplankton or aquatic invertebrates. Increased algal concentrations can decrease available oxygen during the night or under ice cover, or at depth as it decomposes. Decreased water clarity resulting from high algal concentrations can reduce feeding visibility, and elevated algal concentrations often result in a shift from sports fish such as salmonids to less desirable species. Some species of algae can also impart a “muddy” flavour to fish flesh (Nordin, 2001), decreasing the popularity of sports fishing on a given lake.

Phytoplankton samples were collected for all three basins in Comox Lake; the results were summarized and the dominant species for each site are listed in Table 10 to 12. Dominant species were those that made up at least 10% of the total cells present in the sample. The complete results of taxonomic analysis for phytoplankton can be obtained from the MOE office in Nanaimo.

Phytoplankton was sampled 13 times between March 2005 and March 2008. A total of 58 species were identified. Overall the inlet basin tended to have lower plankton concentrations (average of 255 cells/mL) and higher species richness (the number of different species occurring) (average of 48 species). Whereas the main and outlet basin had similar average species richness (38). The outlet basin tended to have higher overall concentrations of plankton (average of 312 cells/mL). In general, algal concentrations were quite low in all three basins, which is typical of oligotrophic lakes.

The phytoplankton community in Comox Lake was dominated most years by diatoms from the Order Centrales, with Cyclotella glomerata and Rhizosolenia eriensis/longiseta comprising the majority of the plankton community in most samples. Pennate diatoms were also common in both the inlet and outlet basins, especially Achnanthes minutissima. During the winter months, a number of species from three other orders (Chlorococcales, Cryptomonadales, and Dinokontae) were present, but they were not seen in significant numbers during the summer months (in the June or August samples). In October, 2005 and 2006, two species of blue-green algae (Anacystis cf elachista var. conferta and Anacystis limneticus, from the Order Chroococcales) were present in significant numbers in all three of the basins. Overall the phytoplankton community found in Comox Lake is consistent with the oligotrophic conditions as indicated by the water chemistry results (Section 6.2.5), therefore no objective is recommended for phytoplankton.

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Chlorophyll a acts as a surrogate for more detailed phytoplankton sampling, as it measures the photosynthetic pigment typically found in phytoplankton. Chlorophyll a concentrations are generally very closely correlated with total phosphorus concentrations (Nordin, 2001). Values below 3 µg/L are considered an indication of low productivity and values above 15 µg/L are generally considered to indicate high productivity. Agriculture, sewage effluent, forest harvesting, urban development and recreational activities can add nutrients to a lake, increasing chlorophyll a concentrations (Cavanagh et al., 1997). Concentrations of chlorophyll a measured in the three basins ranged from < 0.5 µg/L to a maximum of 1.2 µg/L in the main basin. While no objective for phytoplankton is proposed for Comox Lake, we recommend a water quality objective for Comox Lake allowing a maximum of 1.5 µg/L chlorophyll a. Concentrations of chlorophyll a higher than this objective would give an indication that nutrient levels (and therefore productivity) are increasing.

6.3.3 Zooplankton

Phytoplankton are called primary producers, because they are capable of producing their own energy through photosynthesis. Zooplankton represent the second trophic level in a lake, generally preying upon phytoplankton, as well as other zooplankton species. Zooplankton communities are sensitive to changes in phytoplankton community, as well as changes to water quality. They do not have negative impacts on water quality or impair water uses in the way that phytoplankton can, but their species composition and densities can give insights into water quality. Specifically, zooplankton respond to dissolved oxygen concentrations, contaminants and food quality/abundance.

Zooplankton samples were collected 12 times for all three basins in Comox Lake between March 2005 and March 2008, with the exception of the inlet basin where the August 2007 sample was not taken. In addition zooplankton samples for all sites were not collected in June 2007 due to equipment malfunction. The results were summarized and the dominant species (i.e. >10% of sample) for each site are listed in Table 13 to 15. The more detailed set of taxonomic analysis results for zooplankton can be obtained from the MOE office in Nanaimo, BC.

A total of 25 zooplankton species were identified in Comox Lake. Overall zooplankton species richness was similar between the three basins, with an average number of species of 17, 17, and 18 for the inlet, main and outlet basins, respectively. However, the species average density was higher at the outlet basin at 5,916 cells/mL, as compared to the inlet (4,963 cells/mL) and main (5,270 cells/mL) basins. Since zooplankton feed on phytoplankton the higher density observed in the outlet basin is likely linked to the higher concentrations of phytoplankton seen in the outlet basin. Concentrations of zooplankton were highest in the summer and fall and lowest in the March samples.

The zooplankton community of Comox Lake was composed predominately of four groups: rotifers, cladocerans, calanoid copepods and cyclopoid copepods. In all of the basins, the zooplankton community was dominated by three rotifer genera: Keratella cochlearis, Polyarthra, and Synchaeta. Keratella and Polyartha species are known to be cold water rotifers and develop maximal population densities in midwinter to early spring (Wetzel, 2001). Another dominant rotifer, Callotheca, was observed in the summer and fall of 2006 only at all three basins. In addition, Callotheca was identified as a dominant species at the outlet basin only in June 2005 and August 2007.

The dominant calanoid copedod in this study was Diaptomus oregonensis, which was typically only observed in March. During the spring, copepod nauplii (newly hatched copepods) were also very prevalent, dominating the zooplankton population at all three basins. By late summer/early autumn, the small cladoceran, Bosmina longirostris, becomes dominant in response to loss of the thermal stratification in lakes and the increased nutrient regeneration from the deeper waters (Wetzel, 2001). The zooplankton communities observed in Comox Lake are consistent with oligotrophic conditions; therefore, no objective is recommended for zooplankton at this time.

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8.0 MONITORING RECOMMENDATIONS

The recommended water quality monitoring program for Comox Lake is summarized in Table 17. It is recommended that future attainment monitoring occur once every 3-5 years based on staff and funding availability, and whether activities, such as forestry or development, are underway within the watershed.

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In order to capture the periods where water quality concerns are most likely to occur (i.e., fall flush and summer low-flow, as well as spring overturn) we recommend quarterly sampling for a one year period. Samples collected during the winter months should coincide with rain events whenever possible. In this way, the two critical periods (minimum dilution and maximum turbidity), will be monitored.

The monitoring should consist of full water chemistry sampling at the three basin locations (three depths per site – surface, 10 m and one meter from bottom) and include physical measurements of dissolved oxygen, temperature and water clarity. The deep station samples should be analyzed for general water chemistry (including pH, specific conductivity, TSS, turbidity, true colour, TOC, DOC and nutrients) as well as total and dissolved metals (including hardness) concentrations (spring overturn only).

Bacteriological samples (E. coli) should be collected at the seven perimeter sites once weekly for five consecutive weeks in a 30-day period both in late summer and mid-fall.

Biological sampling should continue to be a part of the attainment monitoring program. Chlorophyll a samples should be collected (at surface only) one each sampling date (i.e. quarterly) for all three deep basin sites. Phytoplankton and zooplankton samples should be collected twice per sample year, at spring overturn and during the summer.

In addition, future monitoring should be conducted downstream of Comox Lake in the Puntledge River at the CVRD water intake location. Parameters of concern to monitor include turbidity, TSS, TOC, DOC, nutrients, total and dissolved metals as well as E. coli. Samples should be collected once weekly for five consecutive weeks in a 30-day period both in late summer and mid-fall to capture worst case scenario conditions. Monitoring at this location would examine potential changes in water quality between the lake outlet and the community drinking water river intake located 3.7 km downstream.

 

LITERATURE CITED

Nordin, R.N. 1985. Water Quality Criteria for Nutrients and Algae. B.C. Ministry of Environment, 1985. Victoria, BC. Available online: http://www.env.gov.bc.ca/wat/wq/BCguidelines/nutrients/nutrients.html

 

 

 

 

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