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Aluminum concentrations in Nova Scotia rivers too high for fish health


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One of the rivers studied was West River - Sheet Harbour. For more than a decade this river has been part of an acid rain mitigation effort that has morphed into a complex set of research projects. Here the second lime doser to be installed stands beside one of the branches of this river. Lewis Hinks/ASF

Aluminum concentrations in Nova Scotia rivers are too high to sustain healthy aquatic life, according to a study published recently by a Dalhousie University professor and a team of researchers.

“Long-term, fossil-fuel burning, particularly coal, which is high in sulphur and the sulphur can be transported long distances to Nova Scotia,” Shannon Sterling, a professor in the Earth and Environmental Sciences department at Dalhousie and the lead author of the study, said of the catalyst for bringing out the aluminum concentrations.

Sterling said the aluminum is in the soil, but the acid rain or acid snow that has collected acidic particles from industrial pollution takes the good calcium nutrients out of the soil and allows the release of aluminum concentrations.

“It’s natural in the soil,” Sterling said. “With un-human impacted soils, the aluminum stays in the soil.”

The abstract of the study says elevated aluminium concentrations caused major environmental concern due to aluminium’s toxicity to aquatic life, a major factor that led to the extirpation of wild Atlantic salmon.

Click here to connect to the study web page

Legislation to reduce air pollution that began in the 1990s in North America and in Europe successfully reduced the deposits of acid and the aluminium problem was widely considered solved.

Not so fast, the study found, discovering that freshwater systems show delayed recovery from acidification.

Nova Scotia, one of the regions hardest hit by acid deposit, was originally not considered to have an aluminum problem because of its high soil concentrations of dissolved organic carbon (DOC) that were expected to reduce aluminum concentrations.

But the Sterling-led study shows “widespread and frequent occurrences of aluminum concentrations that exceed thresholds in all sampled rivers despite high DOC concentrations.”

Sterling said it could be that this wasn’t a problem in Nova Scotia years ago but “there is a climate change aspect to it.”

The study showed that the toxic aluminum is even more present where there are high concentrations of DOC.

The study surveyed 10 catchment areas in Nova Scotia — the Mersey River, West River, Moose Pit Brook, Pine Marten Brook, Maria Brook, Brandon Lake Brook, Upper Killag River, Little River, Keef Brook and Colwell Creek. The sampling was done between April 2015 and 2018. The areas studied are predominantly forested with a mix of coniferous and deciduous species and the soils have low acid-neutralizing capacity and relatively high DOC concentrations.

“The highest aluminum levels that our study found were actually in the Eastern Shore, around Sheet Harbour,” Sterling said of the West River drainage system. “They are also high around Keji (Mersey, Medway and Gold rivers) as well.”

Sterling said the aluminum concentrations are likely high across the province but next spring her group will start a larger snapshot survey of more than 70 sites in Nova Scotia.

“That’s (spring) really when it’s critical for the salmon, for the smolts … when the salmon are converting from freshwater to saltwater and they are really sensitive to aluminum. That’s going to tell us more.”

Sterling said the aluminum is toxic to all fish species with the gills providing a pathway inside the fish.

But it’s not all bad news, Sterling said, offering two solutions to the aluminum problem.

“One is to reduce pollution,” she said. “The soils will still take a long time to recover, even if you cut down the pollution. You have to put an antacid on the soils to mitigate the aluminum concentrations. To reduce aluminum you can do what’s called lining.”

Edmund Halfyard, one of the authors of the study, has had success with pouring special antacid rock into the West River, reducing the toxicity for the smolt and allowing them to bounce back.

The long-term solution is to treat the soils by helicopter applications, making the aluminum more solid and less toxic because it is less likely to get on the gills of the fish.

A federal fish restoration program is attempting to determine where aluminum is causing the most problems and treating the soils in those areas.

The cause of the increased aluminum concentrations is just as clear as the potential solution, Sterling said.

The Clean Air Act amended in 1990 in the United States wasn’t enough to clean the air in Nova Scotia, Sterling said.

“A lot of it (acid rain pollution) is from the coal-burning belt in the U.S. and Ontario as well,” Sterling said. “A study and Environment Canada modelling showed most of the pollution that’s causing acid rain in Canada is coming from the Great Lakes region. Since then, Ontario has limited its coal use.”