Sylvan Lake plankton are the food for our fish. Nutrients help them grow. Photo Submitted

Water Quality of Sylvan Lake

The Sylvan Lake Watershed Stewardship Society submits a weekly column about the lake

This is the first of a series of articles on stewardship practices that help us to understand and protect the watershed and its natural assets that the whole community counts on. The Sylvan Lake Watershed Stewardship Society (SLWSS) is the dedicated community guardian of the environment. We do so through vigilance and science.

We monitor the 42 square kilometres (km2) of lake and the surrounding 108 km2 of land inside the watershed perimeter for changes in land and water use that affect the state of the watershed and the people who live and work here. We report the data and our findings at https://slwss.org.

Our partnership with the Alberta Lake Management Society and LakeWatch technicians enables comprehensive sampling and testing during open water seasons.

Lake water quality depends on a few factors: the concentrations of plant nutrients; dissolved and suspended materials that enter the lake in surface runoff; the composition of groundwater; and erosion from along tributaries and the surrounding shore; airborne precipitation and dust; and even nutrients released from lake-bottom sediments.

Sylvan Lake has been sampled and analyzed for 36 years and those data are retrievable from the Alberta Environment and Parks Lake Water Quality online database. Find more details at https://slwss.org

Here are a few highlights of what we know:

Sylvan Lake composition is like the hard groundwater that is pumped from watershed wells for domestic use. The main dissolved ion is bicarbonate at about 370 milligrams per litre (mg/L). In the range 10 to 100 mg/L are sodium, magnesium, carbonate, calcium, and sulphate in that order from high to low.

The Total Dissolved Solids (TDS) concentration of about 360 mg/L means that the whole lake volume of 420 billion litres of water contains about 0.55 million tonnes of soluble minerals. That TDS inventory will slowly increase over time as evaporation concentrates the mineral load. The measured increase of the specific conductivity since 1983 confirms that is happening.

As lake stewards, we pay close attention to changes in the plant nutrient concentrations. Nitrogen, phosphorus, potassium and other elements are essential for growth of the phytoplankton and aquatic plants. They are the food and energy supply for the tiny zooplankton at the bottom of the food chain that swim around in the lake. The Total Phosphorus (TP) concentration is a critical variable as that element can control cosmetically unpleasant and sometimes toxic algal blooms. Historically the Sylvan Lake TP concentration has been about 21 parts per billion (ppb), below the alarm level of 35 ppb.

Since 2016 TP has dropped to about 10 ppb, thereby reclassifying Sylvan Lake from a preferred mesotrophic lake to a lower oligotrophic one, the lowest in rank of lake biodiversity and productivity. Suspended algae concentrations have fallen too, consequently water clarity has increased. With a reduced nutrient and potential food supply, we now watch the condition of the fishery. The concentrations of food-making phytoplankton are measured in the lab by analyzing for the green pigment chlorophyll-a that helpfully converts carbon dioxide to oxygen while its host cyanobacterial cells produce food for the zooplankton population.

Those nutrients and other contaminants enter the lake in tributary flows and as fallout of airborne dust. Golf Course Creek and Northwest Creek are two major streams that capture spring snowmelt and surface water runoff from periods of heavy rain from two large, mainly agricultural, watershed catchment areas. Below-average precipitation in 2018 and to date in 2019 means that stream flow has been well below normal and nutrients have not been replenished at the historical rates. As food-supply plankton die and sink to the bottom of the lake, they remove nutrients from the water column. That further clarifies the lake, although at the expense of the aquatic species that count on a free lunch.

In addition to our tracking the nutrient and chemical composition of the lake, field technicians from Alberta Health sample and test lake water along the Sylvan Lake shoreline to check for biological contamination. If a blue-green algae bloom is detected, beaches may be closed until confirmed safe for public use once again. Beach warnings are posted on the Alberta Health website

Stormwater discharged from land adds contaminants to Sylvan Lake. Land use change, like new subdivisions, alters stormwater flow patterns and rates and potentially flushes more contaminants into the lake. Best stewardship practices for municipalities recommend that contaminants be intercepted and contained or diverted before discharge into Sylvan Lake to affect water quality.

Lake users can contribute to our Society’s stewardship vigilance and science by remaining alert to any changes that you observe while boating or onshore. Whistle-blow at info@slwss.org or call the Alberta Government Environmental Hotline at 1-800-222-6514 with any serious water quality concerns.

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