For decades, permanent and seasonal residents of parts of the Great Lakes, especially Georgian Bay, drank water directly from the lake. Over time, people began to treat lake water in order to be certain of its purity. Today there are even greater concerns.
Isolated bays where the water exchange is slow have tended to be infested with such toxic developments as blue green algae. In some cases local health authorities have forbidden the use of such water for any activities: drinking, food preparation, swimming, and washing of clothing. There is also linkage between sustained low water levels and Increased risk of such algae development.
The following article by Dr. Karl Scheifer , an aquatic biologist interested in aquatic ecosystems and one of our Scientific Advisors provides valuable insights.
Georgian Bay Water Chemistry and Limnology by Dr. Karl Schiefer
As with all of the Great Lakes, there has been a great deal of research and monitoring of water quality in Georgian Bay over the past four or five decades. Much of this is focused on protecting human health related to drinking water sources and water-based recreational activities. Here, our primary interest is in water chemistry as it relates to natural ecosystem functions and aquatic productivity.
The bedrock geology and, to a lesser extent, glacial history of the region has a strong influence on water chemistry in various areas of Georgian Bay. Waters draining the limestone bedrocks of the western shore tend to be very clear, basic (high alkalinity), and high in total dissolved solids, or minerals (“hard” water). By comparison, waters draining the granitic bedrock of the Canadian Shield on the eastern and northern shores of Georgian Bay tend to have a light brown colouration due to the tannic and other acids originating from the numerous bogs and wetlands found on the Shield. These waters also tend to be more acidic because of the acid bog drainage and because the granite bedrock provides little natural buffering for acids. Also, because the granite is far more resistant to weathering than the softer limestone, Shield drainage waters tend to have lower dissolved mineral content (“soft” water).
In most large lakes, the water chemistry is relatively uniform throughout the main lake basin because of wind-driven mixing. This is also true for Georgian Bay, but with one significant and interesting exception. Because rivers draining the Canadian Shield on the eastern coast flow into Georgian Bay within the large island archipelago, mixing of waters is much more variable and less complete. This results in water chemistry gradients within most of the larger bays and channels along the eastern coast.
An example of this is provided above. This is Cognashene Lake, actually a bay on the south-eastern coast of Georgian Bay. Typical of many inlets along this coast, it receives run-off waters from numerous acidic bogs within the watershed and has numerous narrow or shallow channels connecting it with the open lake. These tend to restrict the degree of water mixing in various parts of the bay, resulting in a water chemistry gradient throughout the bay. Closer to the mainland runoff sources, the chemistry of runoff waters prevails. These waters tend to have a light brown colouration, are less clear, are acidic and low in dissolved minerals.
Closer to the open lake waters, the water chemistry of Georgian Bay prevails. These waters are clear and colourless, less acidic (or basic), and higher in alkalinity and dissolved minerals. These influences come from the extensive areas of limestone bedrock on the western shores of the lake.
Those inlets which also receive the discharge of larger rivers, such as the French, Magnatewan, Moon or Musquash, will have an even greater area of inflow water chemistry influence, especially in the spring when river flows and general runoff volumes are greatest.
As runoff and river flows decline through the summer, eastward mixing of lake waters becomes more pronounced due to wind and seiche-related water movements,
In previous sections we have discussed the diversity of physical habitats throughout Georgian Bay, including topography, geology, bathymetry and hydrology. Here we can see that the eastern coast of Georgian Bay also provides a diversity of water chemistry within the aquatic environment, which can further influence biological systems and species diversity.
Water quality in Georgian Bay remains relatively pristine in most areas, but with some noteable exceptions. Severn Sound, in the southeast corner of Georgian Bay, has been the site of a water quality remediation program over the past two decades. This is one of the few areas of Georgian Bay with significant urban development on its shores (Midland, Penetanguishene, Victoria harbour, Port McNicol and Port Severn) and watersheds with agricultural runoff. These had the effect of increasing nutrient levels (eutrophication) in the waters of Severn Sound, which can result in excessive plankton blooms, aquatic plant growth and reduced dissolved oxygen levels. Water quality has improved in Severn Sound over the past 10 years.
The other area of concern involves some of the bays and inlets along the eastern Georgian Bay coast which have higher densities of lakeshore development but lower levels of water exchange with the open lake. Examples include Sturgeon Bay, near Pointe au Baril, where late summer blooms of blue-green alga have caused serious water quality issues in recent years. Ongoing water quality monitoring programs along this coast are important if future water quality problems are to be avoided, especially as lakeshore development continues to increase.
One of the important limnological features of freshwater lakes is the summer thermal regime. This has a major effect on the habitats for many species, especially fish.
As surface waters warm in the spring, a thermocline (zone of rapid water temperature change) develops in the water column, often beginning at 3 to 5 m below the water surface. Below the thermocline, waters remain cold all summer as the thermocline prevents mixing of warmer surface waters with these deeper cold waters. As the summer progresses, surface waters continue to warm, pushing the thermocline deeper. By late summer, the thermocline can be 25 to 30 m below the surface on Georgian Bay. As surface waters cool in the fall, the thermocline breaks down and the colder lake waters can again mix from top to bottom.
On the western coast of Georgian Bay, thermal stratification occurs very close to the coast because of the very deep waters close to shore .With the thermocline abuting this steep coast, the warm water littoral zone (shallow nearshore waters) is very narrow and small in area. As a result, warm water fish such as largemouth bass and northern pike are low in abundance compared to cold water fish species such as whitefish and lake trout.
On the eastern and northern coasts of Georgian Bay, the extensive areas of shallow waters between the islands and in most bays and inlets limits thermal As a result, there is a very wide littoral zone with warm waters from surface to bottom during the summer months. The shelter provided by the islands also allows for the growth of aquatic plants in many areas, including coastal wetlands. This provides excellent and extensive habitat for a wide range of warm water fish species, including largemouth and smallmouth bass, northern pike, muskellunge, walleye, yellow perch, and many others. The cold water fish species are further offshore along this coast, dependent on deeper, cold water habitats.
An important exception is the Big Sound of Parry Sound and adjacent waters. These are some of the deepest waters in all of Georgian Bay (see Section 2.2) and are thermally stratified all summer. As a result, they provide excellent cold water fish habitat which supports some of the highest quality native lake trout and whitefish populations.
As discussed in Section 1.0, the biological component of any ecosystem develops in response to the physical and chemical environments which are available, combined with climate. The topography, geology, soils, and other physical features of the landscape, combined with climatic influences, determine the types of plant communities and plant species (flora) which will thrive in any particular region. This then has a strong influence on the animal communities and animal species (fauna) which will occur in this ecosystem.
In aquatic ecosystems, the same hierarchy of physical, chemical and biological ecosystem components applies. Lake bathymetry and morphometry (basin shape), geology, hydrology, and other physical features, combined with water chemistry and climatic influences, determine the plant and animal species which will naturally exist in any aquatic ecosystem.
In freshwater aquatic systems, the abundance and quality of wetland habitats is especially important for many aquatic organisms, as is discussed in this section. The occurrence and extent of wetland habitats is also a response to many of the physical ecosystem components.
This general discussion of ecosystem structure and function relates to the native species of plants and animals which evolved to occupy specific habitats. Humans have become a major factor in modifying and altering these natural systems. Within the Georgian Bay ecosystem, anthropogenic (human-caused) changes in forest cover, river hydrology, water quality, exploitation and extermination of many native species, and the introduction of large numbers of non-native, invasive species have greatly altered these natural systems. This process is ongoing.