In the past 50 years, eutrophication has become the most serious environmental threat to lakes worldwide. Eutrophication is a common issue in many urban lakes on Vancouver Island including Langford Lake, Elk/Beaver Lake, and Quamichan Lake with deteriorating water quality that is a concern for the ecosystem as well as human health.
Eutrophication is often described as the natural ageing process of lakes in which external sources of nutrients, organic matter, and sediment from the surrounding land accumulate in the lake enhancing its biological production. Under natural circumstances this process takes place in geological time, however under human influences this process can speed up to mere decades, which is known as cultural eutrophication. Nutrient enrichment in a lake from nitrogen and phosphorus causes an accelerated growth of algae and other plant life that produces an imbalance of dominant organisms and water quality; this can result in toxic algae blooms such as a blue-green algae called microcystis (cyanobacteria) that is toxic to most mammals.
The purpose of my study is to create a comprehensive restoration plan for the Municipality of North Cowichan on Quamichan Lake, a shallow and culturally eutrophic lake in North Cowichan, BC. This study is being completed in partnership with the Municipality of North Cowichan (MNC) and Vancouver Island Health (VIHA) to strive for the restoration of Quamichan Lake and many lakes on Vancouver Island that are experiencing human accelerated eutrophication.
To create a restoration plan for Quamichan Lake, current conditions were assessed from April- November 2018 using various field sampling techniques to gather baseline data. In the field, a series of both physical and chemical parameters of water quality were sampled, as well as biological samples of phytoplankton. At each sampling station, water quality was measured for parameters of temperature, dissolved oxygen, conductivity and pH. In addition, water samples were obtained and sent to ALS Labs in Burnaby for analysis of all forms of phosphorus (dissolved orthophosphate, total dissolved phosphate and total phosphorus) and all forms of nitrogen (dissolved inorganic nitrogen, nitrate, nitrite, ammonia, total nitrogen). A turbidity meter was also used to measure total suspended solids, and a secchi disk was used to measure the clarity of the water.
In addition to water quality samples, phytoplankton and chlorophyll-a samples were taken using an integrated tube sampler lowered to 3 m in order to get a mixed sample of the epilimnion for analysis. The tube sampler was lowered to 3m twice and emptied into a bucket. These biological samples are important in assessing the biomass of algae and the species of algae present in order to understand the lakes trophic status.
Restoring a eutrophic lake to a mesotrophic state is a complex process that will require many years of restoration and monitoring as well as interdisciplinary efforts from governance, science, and the public. In order to restore a lake, catchment basin management efforts need to be taken to reduce the external load in addition to internal lake techniques. Restoration for a lake the size of Quamichan will take decades to accomplish. In addition, long-term monitoring of the water quality and algae biomass is an important aspect to ensure restoration success. The end goal of this project is to provide MNC with restoration and monitoring options that will be feasible and successful to apply to Quamichan Lake.