[Note: The following was first published in the June 2013 Alberta Outdoorsmen.]
Copyright © 2013 Don H. Meredith; Photos courtesy of Dr. Ron Zurawell, All Rights Reserved.
For microscopic organisms, they create a lot of havoc in lakes and ponds. They mess-up beaches; foul boats, motors, ropes and nets; sicken and kill fish, wildlife, livestock and pets; and ruin a summer day at the lakeshore. They are the so-called “blue-green algae” that infect more and more Alberta lakes every summer.
As Dr. Ron Zurawell of Alberta Environment and Sustainable Resource Development (ESRD) explained, the name “algae” is a misnomer. They are actually a form of bacteria, cyanobacteria (cyan = blue-green) to be exact. Cyanobacteria contain chlorophyll and thus can make their own food like algae and other green plants. Dr. Zurawell recently made a presentation on the health effects of cyanobacteria at the University of Alberta for the Alberta Lake Management and the North Saskatchewan River Keeper societies, where he explained why and how these bacteria become problems in Alberta lakes.
Although microscopic, these bacteria species create large, visible colonies, many of which form mucilage mats on surface water. The bacteria prefer to stay near the surface so they can get as many nutrients and sunlight as possible for their photosynthetic processes. The nutrients they use include bicarbonate (HCO3-) which cyanobacteria are specifically efficient at taking up. Bicarbonate is prevalent in water bodies with high alkalinity (high pH) conditions.
Alberta’s prairie recreational lakes offer ideal conditions for cyanobacteria. First, they are situated in glacial basins rich in nutrients, such as phosphorous and bicarbonate. Second, they tend to be shallow where there is little temperature stratification from top to bottom. This increase in summer temperature at the bottom increases nutrient loading from bottom sediments. As well, there is intense development of the watersheds surrounding lakes, increasing nutrient loading into the lakes.
Another factor that favors the development of cyanobacteria in our lakes is the long retention time the water spends in the lakes. Many of these lakes hold water for 50 or more years. There is little flushing of the water from the lakes. The water that does leave does so through evaporation or occasionally through an intermittent outlet stream. Thus, the nutrients accumulate in the water.
Cyanobacteria are not the only organisms that benefit from these nutrients; most aquatic plants benefit. As well, the animals that feed on plants for food benefit. However, there are very few animals that eat cyanobacteria, most likely because of the toxins the bacteria contain. Indeed, toxicity is what is most concerning about this bacteria.
It turns out these bacteria produce many toxins, depending on the species. The toxins can be broken down into three groups based on how they affect animals: dermatotoxins that attack the skin, neurotoxins that attack the nervous system, and hepatotoxins that attack the liver.
Dermatotoxins can cause mild to severe reactions in humans, including irritations to eye, ear and throat; rashes and skin lesions. For example, late summer “swimmer’s itch” is most likely caused by a cyanobacteria dermatotoxin. Early season swimmer’s itch is caused by an allergic reaction to a misdirected duck parasite and is usually not an issue in Alberta lakes much after early July. However, if it is late summer and there is a bloom of cyanobacteria, the irritation is most likely caused by a dermatotoxin.
Skin irritation is one thing but attacking the nervous system is another. Cyanobacterial neurotoxins can cause paralysis, seizure and death, depending on the amount of toxin consumed. Many deaths of dogs, other pets and livestock along lakeshores in late summer can be attributed to the ingestion of cyanobacterial neurotoxins from lake water.
Hepatotoxins can also be quite deadly, as they attack an animal’s liver, whether that animal be fish, fowl or person. One such toxin, Microcystin is very persistent, having a very stable chemical structure, and will survive boiling or freezing. So, boiling lake water to drink does not remove the toxin as a threat. Dr. Zurawell, who has been sampling Alberta lakes for many years, showed that the occurrence of Microcystin in Alberta lakes has been increasing over the years.
Because the fish in a water body blooming with cyanobacteria are exposed to these chemicals steadily, they are one of the first animals to indicate the presence of toxins in the water. Sickly fish with skin lesions and deteriorating livers are some of the symptoms that can be observed. Cyanobacterial toxins can also be responsible for many late summer fish die-off’s, along with the loss of oxygen that occurs when these blooms die.
These toxins are not just threats to fish, wildlife and pets. We humans are also susceptible. All algal/bacterial blooms should be treated with caution. Affected lake water should not be used for domestic purposes, such as drinking, cooking or bathing/showering. Don’t swim in such water, keep pets and livestock away, and provide alternative drinking-water sources. Don’t eat fish from such water.
Although the eutrophication of our prairie lakes is a natural occurrence, it can be slowed if watershed development is controlled such that nutrient loading of the lake water is restricted. That would take some cooperation and willingness to act on the part of our governments. However, as I discussed last month in this column, once a lake has crossed the tipping point where cyanobacteria dominates the lake, it is very difficult to bring the lake back to a healthier condition. That hasn’t stopped the users of at least one lake to try.
In the early 1990s, users of Pine Lake, a small eutrophic lake southeast of Red Deer, complained to the government about what was happening to their lake with regard to increasing blooms of cyanobacteria. Alberta Environment decided to step up and use the lake as a pilot study for how lakes might be managed to return them to better health. An advisory committee, made up of members of the community, was formed and a diagnostic study was done in 1992 to determine the sources of the nutrients (mostly phosphorous) and possible mitigations. The study determined that approximately 61% of the phosphorous loading was from lake sediment and 36% from surface runoff (Sosiak and Trew, 1996, “Pine Lake Restoration Project: Diagnostic Study”, Alberta Environment). The advisory committee formed the Pine Lake Restoration Society which developed a work plan and raised funds.
In short, steps were taken to reduce nutrient loading into the streams that enter the lake and remove the phosphorous that was already in the lake. In the latter case, a system that was first tried in Europe called “hypolimnetic withdrawal” was adopted. The phosphorous-rich water at the bottom of the lake was removed by a gravity-fed, valve-controlled pipeline. To date, results have been mixed. Although cyanobacteria blooms still occur in the lake, they are not as severe. The water chemistry varies from year to year, most likely due to factors outside of the control of this program (such as increased precipitation and runoff in some years) (“Pine Lake 2006 Report,” Alberta Lake Management Society). So, the jury is still out on the effectiveness of the program.
One thing is certain: if steps aren’t taken to reduce nutrient loading occurring in our lakes, cyanobacterial blooms will be common in most. It just depends on which side of the tipping point you want to work from.