Mystery of Nova Scotia river toxicity solved: Environment Canada report

Salmon attempt to leap up(Photo by Jeff J Mitchell/Getty Images)
Recent years have seen world-wide improvements in the acidity of lakes and rivers, due to cuts in emissions of sulphur dioxide and nitrogen oxide. However, according to an Environment Canada report, one region has not seen the same improvement — southern Nova Scotia.

"This is the only part of the world where acidity is not improving with major cuts in acid rain emissions," said Tom Clair, according to CBC News. Clair is an Environment Canada research scientist who studies the effects of air pollution on aquatic ecosystems.

The reason behind this region's lack of improvement? Toxic aluminum.

On its own, aluminum is fairly safe, although it is highly reactive. This high reactivity means that even though it is abundant in nature, it is only rarely found in its pure form. Reactions with acid rain, though, cause aluminum to be released from the soil and it builds up in the ground water, and in streams, rivers and lakes. These high levels of aluminum in the water are very toxic to fish.

Researchers have shown that dissolved organic carbon can reduce the toxicity of aluminum in the water. However, carbon is not a solution in this region. Clair tested the waters from 92 rivers in the Atlantic provinces and found that salmon populations in seven southern Nova Scotia rivers were suffering the greatest losses, due to aluminum released by acid rain.

[ Related: Salmon returned to eastern P.E.I. river ]

"We realized that carbon is not enough to protect the fish from aluminum in that part of the world. It was surprising," Clair said.

Clair's report has sparked a new effort to clean up the waters of those rivers, and this has started along Lunenburg County's Gold River. Dr Shannon Stirling and her team from Dalhousie University and students from New Germany Rural High School are testing a 'catchment liming' project, spreading 30 tonnes of crushed limestone along the banks of one of the river's tributaries.

"It's a long-term solution that doesn't need to be maintained. It's one application that lasts for 50 years," Stirling said.

According to the CBC News article, samples taken since the liming show improvements in the pH of the water, but results of the aluminum content have yet to come back.

"The results we are seeing are encouraging. There is hope for the Atlantic salmon." said Stirling.

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Clair supports the idea of liming the tributaries, since those are typically the habitat for breeding salmon, but sees liming large rivers as impractical.

"The chemistry in those rivers probably won't come back for another 100 years to the point where they were before acid rain started," he said. "The poor fish. They are in for a rough ride."

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