Connecting you with the sanctuary
Swan Lake Water Quality
Written and narrated by Rob Bowen, the principal of Diversified Scientific Solutions here in Victoria.
Zooplankton Copepod with Eggs
by Rob Bowen
I’ve been studying water quality at Swan Lake since 2016 and am fascinated with the seasonal changes that occur each year at the lake. When we look at the lake, we often notice just the surface of the water but there’s so much more going on below the surface. In fact, under the lens of a microscope, a single drop of water reveals an aquatic world teaming with life. These small organisms are a vital part of the food web providing nourishment to aquatic insects which in turn provides food for amphibians, reptiles, fish, mink and even otter. All these organisms depend on the health or quality of the water much like we depend on the air we breathe. But how can we know the quality of the lake unless we first learn how the lake as a whole works, its biology, chemistry and physical properties.
Algae
by Rob Bowen
Swan Lake covers an area of about 23 acres. Its maximum depth is about 6 meters. It has two main creeks; one flows into the eastern part of the lake called Blenkinsop Creek and the other flows out of the western part of the lake called Swan Creek. The water quality of Swan Lake has significant impacts on the health and biodiversity of the lake and its surrounding ecosystems. As with many urban wetlands, Swan Lake concentrates wildlife and supplies vital nursery areas, food sources and large varieties of protected habitat in the midst of an increasingly developed landscape. Additional values of this feature are far reaching as Swan Lake gives rest to migratory birds, provides water filtration and flood control, enables aquatic transitioning for insects and amphibian species such as aquatic dragonfly larvae to flying dragonflies and tadpoles to emerging frogs, and provides educational opportunities to observe the many aspects of a lake ecosystem. Human impacts have changed the state of the health of this lake over time. Prior to the early 1900s, people swam, skated and fished the lake, and local residents recall the lake as being clear and free from algal growths we call blooms. In 1927, a winery was constructed on Quadra Street and effluence or liquid wastes from this winery began to drain into the lake creating negative impacts on the water quality of the lake. Significant areas upstream of the lake introduced agricultural fertilizers or nutrients that, through a series of connecting creeks drained into Blenkinsop Creek and then into Swan Lake. These nutrients, as well as other elements from urban sources such as lawn fertilizers and septic fields, have over time created a highly nutrient rich or eutrophic aquatic system characterized by high turbidity or water clarity, elevated phosphorus levels, and at times low dissolved oxygen concentrations. During the typical dry summers of Victoria, algal blooms are common and on occasion fish kills occur where lake temperatures, dissolved oxygen, algal overgrowth and nutrient imbalances result in conditions that exceed tolerance levels for fish and a host of organisms. During these algal blooms, visitors to the walkways around the lake can at times smell a pungent odor emitted from decaying bio mats that cover large parts of the lake and shore margins. It is quite common for the western end of the lake to be completely covered in duckweed. As a result, the overall health and biodiversity of the wetland area is significantly impacted by these summer extreme conditions that are measurable in the water quality of the lake. Changes in the water quality of the lake can be subtle or dramatic, human induced or climatic.
Rob Bowen
To better understand the processes at work within the lake and to observe temporal changes, water quality studies have been conducted on the lake since as early as the 1960s with several short-term studies since that time. In 2016, a new water quality sampling program was initiated to consistently measure such parameters as dissolved oxygen, pH, oxygen reduction potential, nutrients, light penetration and temperature. In addition, net samples are collected to look at algae populations as well as zooplankton species. During the summer, Swan Lake has large populations of blue-green algae or cyanobacteria, which have the potential to produce toxins or harmful algal blooms. These toxins can be harmful to humans and animals such as pets and are responsible for many beach closures at lakes in Victoria and around the world. In order to improve the water quality conditions at Swan Lake, it's important to continually and consistently monitor the water properties to unravel the mysteries of the lake. Such studies lead to a greater understanding of the processes at work at Swan Lake. With this science-based approach, future improvements such as how to reduce the amount of phosphorus from entering the lake and how to reduce the potential of harmful algal blooms can be considered focusing on the unique characteristics of Swan Lake.
Rob Bowen