The SLPTA volunteer-led WQ monitoring program measures many physical, chemical andbiological characteristics of the lake water over much of the ice-free season. The importance of monitoring certain key parameters is described below.

Water Temperature: Temperature is the key physical parameter controlling the rate of most chemical and biological processes, including the metabolism of all living cells. Precise ranges of temperature trigger migration, reproduction, and life cycle stages of many species. At our temperate latitude, the onset of spring brings longer days which warm the upper water layer.
Fair weather reduces the wind energy available to mix the warm layer with the cooler water below and a thermocline zone will develop in all but the shallowest lakes. This zone is characterized by a rapid change in temperature over a small change in depth. The surface layer deepens over summer, but the thermocline generally remains stable as a warm upper layer over denser colder water. This condition persists until cooler fall weather and strong winds introduce the energy required to re-mix the lake. Higher temperatures reduce oxygen concentration and the increase the rate of chemical processes which can stress aquatic species. Thus temperature influences overall ecosystem health and diversity.

Dissolved Oxygen DO: Dissolved oxygen is a measure of the amount of oxygen available for
aquatic life to respire, and for organic oxidation (decay process). Oxygen levels are strongly
dependant on temperature, with cold water able to dissolve much higher levels of oxygen than
warm water. Algae and aquatic plants produce oxygen via the photosynthesis process. Oxygen
production by plants can often exceed the saturation capacity of the water to absorb it.
However, with thermocline development in the warmer months, the deeper colder water of the
lake is cut off. It doesn’t support plant growth, nor receive additional oxygen from the surface.
As deep-dwelling organisms consume the available oxygen, levels decrease in the deeper
water as part of the normal seasonal cycle. At greater depths, very low Oxygen levels can
persist year-round, indicating a stressed (anoxic) lake. life. Minimum levels are required for
survival of some species. Levels below 6.5 mg/L are considered unhealthy, will negatively
impact aquatic life and affect most fish.

Conductivity: Electrical conductivity refers to the water’s ability to transmit an electrical current
over a specific distance. Water conductivity is strongly associated with temperature and salinity.
It is an indicator of the concentration of dissolved salts such as chlorides, sulfides, and other
electrically charged ions dissolved in the lake water. Human inputs such as road salt and soil
disturbance tend to increase the level of dissolved solids which results in increased conductivity.
In coastal areas, natural events such as hurricanes and major windstorms can transport sea
water aerosols long distances inland. Elevated conductivity may be an indicator for other
chemical impairments which collectively can stress the osmotic equilibrium of aquatic species. A
significant localized change in conductivity (usually an increase) may indicate a point-source
discharge.

Metals: Metals are introduced by the natural weathering or erosion of soils and rocks, or at
accelerated rates due to ground disruption activities such as construction, forestry and farming.
Some metals are required in trace amounts by most aquatic species while others can be toxic.
Metals do not break down and can move between lake water and sediments or be bio-
concentrated in animal or plant tissue. Temperature and pH influence the mobility of metals.
pH: The pH value of water is a measure of Hydrogen ion activity, which reflects the acidity or
alkalinity of the water. The pH range considered normal and healthy for lakes is above 6.5 and
below 9.0 (on a scale from one to fourteen). The rates of physical-chemical and bio-chemical
processes are sensitive to the pH level. Changes to pH can impact the uptake or release of
nutrients or toxins into the water. The pH of lake water varies naturally depending on local
geology or when there are large amounts of plants which release carbon dioxide as they die and
decompose. When carbon dioxide mixes with water, a weak carbonic acid is formed which can
lower the pH of the lake. In general, if a lake is slightly alkaline (pH 8.0 or above), it has higher
capacity to buffer acids from natural or human activities (eg. sulfur dioxide and nitrogen oxides
emitted by industrial operations and vehicles).

Total Dissolved Solids (TDS): Dissolved solids can be anything from naturally occurring
organic material, to minerals and pollutants. Total Dissolved Solids represents the sum
concentration of dissolved substances, typically inorganic salts and small amounts of organic
matter. Common inorganic salts found in water include calcium, magnesium, potassium and
sodium (+ve charge ions), and carbonates, nitrates, bicarbonates, chlorides and sulfates (-ve
charge ions). Dissolved solids can produce hard water, which leaves deposits and films on hot
water pipes and boilers. High levels of dissolved solids can reduce the diversity of aquatic life
and may indicate contamination by municipal or industrial runoff.

Nutrients: It’s important to monitor nutrients because they control the rates of primary
production in aquatic systems. After Carbon, Hydrogen and Oxygen, the key macronutrients
required for plant growth are Phosphorus (P) and Nitrogen (N). Natural sources of Phosphorus
and Nitrogen come from decay cycles, land run-off and organic sediment. Unnatural
enrichment may include chemical fertilizers, municipal sewerage and livestock manure. In the
equilibrium state of most ecosystems, Phosphorus is generally the limiting nutrient. The
introduction of large doses of Phosphorus (fertilizer) can lead to rapid algae blooms including
blue-green algae and growth of aquatic plants. As these plants die off and decompose following
normal seasonal cycles, their decay leads to high demand for Oxygen to feed biological
processes (biological oxygen demand = BOD). High BOD reduces the amount of dissolved

Oxygen available for fish and other aquatic organisms. The effect is most noticeable at the
bottom of deeper basins where mixing energy is very low.

Chlorophyll a: We measure chlorophyll a as it is a key indicator of primary production.
Chlorophyll a is a pigment found in green plants and algae which enables photosynthesis, the
conversion of sunlight into primary organic compounds. Essentially, Chlorophyll makes food.
Algae are a natural part of the environment and usually the first organisms to respond to the
introduction of key nutrients such as Phosphorus and Nitrogen by blooming rapidly. Algae
produce oxygen as they grow, but the process of decomposition consumes oxygen, slowly
reducing dissolved oxygen in poorly mixed water. Excessive algal growth can lead to issues
such as surface scums, unpleasant odors and the release of toxins which, when present in high
enough concentrations, may pose a health risk to vertebrates. The chlorophyll a threshold for
impacts on fish is generally considered to be 100 ug/L.4. The cleanest lakes will have
chlorophyll-a levels of less than 5 ug/L.

Coliform Bacteria (E. coli): The bacterium E. coli is measured as an indicator for the potential
presence of disease pathogens from municipal wastewater or other sources. These bacteria live
in the digestive tract of all warm-blooded animals and are monitored because they are easily
cultured in the lab. Survival of E. coli in the aquatic environment is dependent on factors such as
temperature, exposure to sunlight, available nutrients, pH, salinity and even predation by other
microorganisms. As a result, samples must be cooled and processed rapidly for testing to be
valid. Regional recreational water quality guidelines for average E. coli abundance vary across
Canada. The range between about 100-200 CFU per 100 mL of water is the threshold level of
acceptable low risk of contracting a gastrointestinal illness.