As many Manitobans know, nothing spoils a trip to the lake like the algal blooms. New research has found the phosphorus that causes the problem can linger for years in the mud at the bottom lakes before being recirculated back into the water to further pollute the lake.
And researchers say Manitoba lakes are among the most susceptible to the problem.
"What our study was looking at was the process of recycling the phosphorus in the sediments back up into the water column so that phosphorus that we think should be locked away actually moves back up into the water column and can contribute to algal blooms," explains University of Winnipeg assistant professor Nora Casson, who co-authored the study published in the Canadian Journal of Fisheries and Aquatic Sciences Wednesday.
"This is a problem because it means that phosphorus that's coming in from the landscape isn't just going to cause algal blooms today or that summer, it could result in poor water quality for years or decades to come."
Algal blooms can have a negative effect on recreation activities, drinking water, property values and wildlife, and can put the health of both humans and animals at risk, says Casson.
Scientists have known since the 1970s that nutrient phosphorus causes the blue-green globs of muck. But even after regulations and improved sewage treatment went into effect to counteract the problem, the blooms continued to grow in lakes across the country.
That led scientists to look into whether phosphorus might be being recirculated back into the water, and the study released this week set out to better understand where, when, and why this process occurs in Canadian fresh waters.
For the study researchers reviewed data from 70 water bodies and found the recirculation of phosphorus — known as internal phosphorus loading — is a common phenomenon in Canadian fresh waters. But the rates of the process varied dramatically from lake to lake.
The researchers looked at data from Lake Simcoe, Lake Winnipeg, Lake of the Woods, Lake Erie, Lake Champlain, Cootes Paradise, and Lake Diefenbaker for the article.
The highest rates of internal phosphorus loading were found in small prairie lakes in Manitoba, Saskatchewan and Alberta, while the lowest rates were found in Canadian Shield lakes in Ontario and the Maritimes.
"There are a few different conditions that would make a lake susceptible to having higher rates of internal phosphorus loading, and the Manitoba lakes have all of them," said Casson.
Casson said lakes that are underlain with sedimentary rock — like those found in Manitoba — allow phosphorus to be released from the mud at the bottom much more easily than harder rock.
She said the pH levels of Manitoba's lakes are also perfectly suited for internal phosphorus loading, and the relatively small and shallow size of our lakes compounds the problem because it means they're more easily stirred up by winds, which further promotes the process.
Consequences for 'many, many years to come'
While the researchers say not much can be done to stop internal phosphorus loading or the algal blooms they cause — short of making sure phosphorus doesn't end up in our lakes in the first place — Cassons is hopeful the research will help us better manage the problem.
"The results of our study suggest two things: number one, if you have phosphorus going into a lake, we're going to see the consequences of that for many, many years to come and so we should think very carefully about what we do in the landscape to avoid polluting our lakes," she said.
"And the second thing is you can use the results of this study to predict how lakes are going to recover if you were to cut-off all the phosphorus pollution, and some lakes would recover much more quickly than other lakes."