Quinte waters in the broader context of the Great Lakes
An examination of of some historical and contemporary aspects; shipping and the environment [*]
Example of eutrophication
[click image to enlarge]
Eutrophication is the scientific term for nutrient enrichment. The large amounts of phosphorus in the Bay lead to excessive algal production, of which the effects include; reduced oxygen levels, reduced water clarity and bad smelling/tasting drinking water 17. As a result of these changed conditions, foreign species begin to inhabit the area. Phosphorus pollution was noted as being serious in the 1930s 18.
[Review 2020] Eutrophication is a major stressor that may facilitate the establishment of some non-indigenous species, but the arrival of species is largely unrelated to eutrophication.
The main source of phosphorus pollution is discharge from sewage treatment plants 19. Sewage goes through a primary treatment, where it passes through screens and shredders into a settling tank, forming ‘sludge’. Sludge is mainly composed of human, industrial and household waste, though it may contain numerous chemicals dumped illegally into the sewer 20. Secondary treatment bacterially removes most of the solids and carbon, so the organic matter becomes inorganic. After the secondary treatment, sewage does not carry disease or offensive odour, but it still contains phosphorus 21. Originally, raw sewage was dumped into water and for most of the 20th C. sewage treatment plants only employed primary treatment. From 1940-1960, six sewage treatment plants were built around the Bay of Quinte area, and all of them dumped their treated sewage into the Bay. In 1965, 215 kg of phosphorus was entering the Bay of Quinte per day as a result of sewage 22. In 1970, the IJC blamed excessive phosphorus as the root cause of Great Lakes eutrophication 23.
Prince Edward County; areas affected by
sewage treatment [click image to enlarge]
Agricultural runoff can also be blamed for high phosphorus levels in the Bay of Quinte. Runoff is comprised of pesticides, fertilisers, manure and sediments, often containing high levels of phosphorus. Phosphorus from agricultural runoff can be a concern if it seeps into groundwater. Nitrogen is also capable of increasing eutrophication in large amounts, but it is vital in maintaining a balanced lake environment. An optimally balanced lake will have a ‘Nitrogen to Phosphorus’ ratio of 10:1 24.
[Review 2020] Pesticides and sediment are not major sources of phosphorus. They are components of runoff.
[Review 2020] Phosphorus is the limiting nutrient in freshwater (nitrogen is not) although both stimulate plant and algae growth. Nitrates and ammonia are toxic, and elevated nitrogen in aquatic systems stimulates cyanobacteria (blue-green algae) which can be toxic when it dies. The blue-green algae blooms are the basis of the water advisories in the Bay of Quinte region. But phosphorus is what we are typically concerned about when we talk about eutrophication.
Different aquatic species tend to overtake eutrophied areas, because they prefer the shade that extra algal growth can provide. In the 1950s, walleye became the new pre-eminent fish in the Bay of Quinte because they prefer the shaded areas with high algal density 25. But high algal density also limits macrophyte production, meaning the walleye’s food source was drastically reduced. As a result, walleye populations decreased. In 1955, piscivorous (fish-eating) lamprey overran the Bay of Quinte. The lamprey flourished and did serious damage to the Bay’s fish population, so the Great Lakes Fisheries Commission undertook a program to control sea lamprey in 1954. The program was successful and the lamprey population was reduced by 90% after the use of chemical lampricide 3-trifluoromethyl-4-nitrophenolin (TFM) in the 1970s 26. Soon after, non-native white perch replaced lampreys as the Bay of Quinte’s dominant piscivorous species. White perch consumed many of the Bay’s algae-grazing fish, which was counterproductive to the water’s eutrophication problem. In 1978, there was resurgence in walleye and a collapse of the white perch population, coinciding with a major reduction in phosphorus output from sewage treatment plants. Algal density has been declining in the Bay of Quinte as a result of the renewed Great Lakes Water Quality Agreement, but still not enough to promote species diversity 27.
[Review 2020] Walleye prefer turbid waters, but not necessarily high algae. Walleye are visual predators who feed in open water areas not in “weeds”. However, the food fish they eat seek refuge in the weeds.
[Review 2020] Sea lamprey is a parasite not a piscivore (fish-eating) fish.
[Review 2020] White perch were first reported in the Bay of Quinte in 1952 (not 1970s). A climatic window (mild winters) likely permitted their invasion and establishment; low predator (walleye) abundance allowed them to flourish. Severe winters of 1977 and 1978 resulted in a significant overwinter mortality event that greatly reduced white perch abundance and favoured recruitment of walleye. Higher walleye numbers suppressed white perch from again becoming abundant. Phosphorus reduction was not a major factor in the species change.
23 [back] The Great Lakes: An Environmental Atlas
26 [back] The Great Lakes: An Environmental Atlas
* [back] - This project was developed by Isabel Slone (one of the Society's 2007 "summer students") and was in part funded with a grant from Young Canada Works, in part with a grant from the Municipality of the County of Prince Edward, and in part with this Society's research funds.