Ecosystems
What Types of Freshwater Aquatic Ecosystem do we have in Canada?
Canada contains an abundance of freshwater ecosystems, including lakes, ponds, rivers, streams, prairie potholes, and wetlands.
A lake is a sizable water body surrounded by land and fed by rivers, springs, or local precipitation. The broad geographical distribution of lakes across Canada is primarily the result of extensive glaciation in the past.
Lakes can be classified on the basis of a variety of features, including their formation and their chemical or biological condition. One such classification identifies two types of lakes: Oligotrophic and eutrophic. Oligotrophic lakes are characterized by relatively low productivity and are dominated by cold-water bottom fish such as lake trout. Eutrophic lakes, which are shallower, are more productive and are dominated by warm-water fish such as bass. Great Slave Lake (Northwest Territories) and most prairie lakes represent the two types, respectively. Ponds are smaller bodies of still water located in natural hollows, such as limestone sinks, or that result from the building of dams, either by humans or beavers.
Ponds are found in most regions and may exist either seasonally or persist from year to year. Rivers and streams are bodies of fresh, flowing water. The water runs permanently or seasonally within a natural channel into another body of water such as a lake, sea, or ocean.
Rivers and streams are generally more oxygenated swiftly moving waters (e.g., black fly larva and darter fish.). Some of the larger rivers in Canada include the St. Lawrence, Mackenzie, Fraser, Athabasca, North and South Saskatchewan, and Saint John rivers.
Some rivers flow into oceans, the great saltwater bodies that cover 70% of the earth's surface. The tidal areas where saltwater and fresh water meet are called estuaries. These productive ecosystems, found on Canada's coasts, contain unique assemblages of organisms, including starfish and anemones.
How does an Ecosystem Work?
Energy from the sun is the driving force of an ecosystem. This light energy is captured by primary producers (mainly green plants and algae) and converted by a process called photosynthesis into chemical energy such as carbohydrates.
The chemical energy is then used by the plants to perform a variety of functions including the production of plant parts such as leaves, stems, and flowers. The raw materials used for this purpose are nutrients (e.g., nitrogen, phosphorus, oxygen, and calcium): substances necessary for the growth of all plants and animals.
Animals are incapable of photosynthesis. They therefore eat plants, other animals, or dead tissue to obtain their energy and required nutrients. In ecosystems, the transfer of energy and nutrients from plants to animals occurs along pathways called food chains. The first link in a food chain consists of primary producers: green plants and other organisms capable of photosynthesis.
Plant-eating organisms, known as primary consumers: carnivores (flesh eaters) or omnivores (plant and animal eaters). Decomposers such as bacteria and fungi make up the final link in the food chain. They break down dead tissues and cells, providing nutrients for a new generation of producers.
Most organisms in an ecosystem have more than one food source (e.g., fish feed on both insects and plants) and therefore belong to more than one food chain. The consequent overlapping food chains make up food webs: complex phenomena with links that are constantly changing.
The above information was provided courtesy of Environment Canada (Learn more by visiting their Aquatic Ecosystems pages at http://www.ec.gc.ca/water/en/nature/aqua/e_aqua.htm)
