[Canada] Canadian prairie lakes prone to infections of blue-green algae could potentially benefit from a new treatment highlighted in a University of Alberta study.
The newly published research found the addition of iron to the lakes can inhibit the release of phosphorous from the sediment, halting the process that generates algal blooms.
“The relationship was what we call a dose-response relationship, meaning that when we added a little bit of iron, not much happened, but as we added more and more we saw a linear relationship,” said lead author Diane Orihel, who conducted the experiments for her PhD project. “The greatest amount of iron resulted in the greatest amount phosphorous sequestration in sediment.”
“Our research suggests that iron treatment is a potential remediation strategy.”
Many Alberta cottage owners are familiar with blue-green algae, which is a type of bacteria that tends to affect lakes in the summer. Water turns a sickly green colour, foul odours are produced and aquatic wildlife is compromised. Most concerning, the bug generates a toxin called microcystin that can cause serious liver damage to humans.
Central Alberta lakes are particularly susceptible to algal infections, in part because they tend to be shallow, but also because they are lined with sediment that is excessively rich in nutrients such as phosphorous and nitrogen. Some of these nutrients are naturally occurring, but much of it comes from human activity such as shoreline development and farming.
“We, through our activities, have produced more algal blooms because we release sewage to lakes, we apply fertilizers to agricultural fields and to our own lawns … and all this washes into lakes, increasing the nutrient supply,” said Orihel, a freshwater ecologist who is now a post-doctoral fellow at the University of Ottawa.
When conditions are right, the phosphorous gets released and stirred up in the lake, providing the fuel the bacteria needs to grow.
Orihel chose to use Nakamun Lake, 100 kilometres northwest of Edmonton, for her experiments because it has some of the highest microcystin concentrations of lakes across the country.
The idea to try iron as a remedy came from previous work she did at an experimental lake in Ontario known as Lake 227. Though phosphorous has been continually added to the lake since the 1960s, it has remained effectively sequestered in the sediment, possibly because the lake has a naturally high concentration of dissolved iron.
It has long been known that iron has properties that inhibit phosphorous from being released.
Orihel conducted her experiments by equipping the Nakamun Lake with 15 “mesocosms,” which are essentially large test tubes two metres in diameter and six metres deep.
Differing amounts of iron were added to each mesocosm through a liquid known as ferric chloride.
“It’s actually used in the treatment of sewage so this is an easily accessible and relatively inexpensive product to purchase,” Orihel said.
The results showed that the addition of iron at higher levels was most effective at controlling the release of phosphorous. She said the discovery may be particularly value for Canadian prairie lakes, since many of that type with high phosphorous loads can take decades to recover — even if external sources of phosphorous are reduced.
“This is not a silver-bullet solution. It needs to be used in conjunction with cleaning up sources of phosphorous in the watershed,” she said. “But the reason I did the study is to come up with a technique that will complement (that effort) so we see timely improvement in water quality.”
The research is published in this month’s edition of Ecological Applications.
Photo: University of Alberta conducts experiments on Nakamun Lake in central Alberta using mesocosms, which act as big test tubes in lakes. The experiments are on blue-green algae blooms.