Rising levels of chloride, aluminum in Halifax lakes a concern, study says

Levels of chloride, arsenic and aluminum in some Halifax lakes are a concern, according to a newly published Dalhousie University study.

The peer-reviewed study examined four decades of water quality data from 50 lakes.

It says that concentrations of aluminum in 29 per cent of the lakes, chloride in 20 per cent of the lakes and arsenic in one lake exceeded Canadian aquatic life protection guidelines.

The lead researcher said rising chloride levels have a "huge impact" on a lake ecosystem because aquatic life is used to a certain level of salinization.

"When you increase chloride levels," Rob Jamieson said, "you kind of disrupt that environment and you create an opportunity for organisms that are more tolerant of those chloride levels to become more dominant in the ecosystem." 

Jamieson also said higher chloride levels probably would not directly harm fish that live in the lakes, but it could affect organisms that they rely on for food.

He added that other researchers have found that blue-green algae, which produce toxins harmful to people and pets, are more tolerant of higher chloride levels and could become more of a problem.

The study identified urban development as a possible reason for rising concentrations of substances like chloride.

For example, clearing forests and paving surfaces for new subdivisions leads to more runoff, which carries pollutants into nearby lakes. 

New roads also need to be salted to keep roads safe in winter.

Environmental monitoring is important

The Halifax Regional Municipality supported the Dalhousie study by paying for a helicopter, allowing researchers to collect samples quickly.  

Emma Wattie, a manager in HRM's environment and climate change team, said it's important to monitor lake water so human impacts on ecosystems can be detected before it's too late to make changes.

"We can't do anything if we don't know what's happening in our lakes," Wattie said. 

She added that data can help the city make decisions, such as what products are used as fertilizers or where to build housing.

"Knowing the quality of certain lakes can help us kind of decide where we should be … investing in our communities," Wattie said.

There are over 1,000 lakes in the municipality, she said.

Despite the concerns raised by the study, Jamieson said that on the whole "water quality and lakes around the Halifax area [are] generally very good, and this water quality supports a number of recreational activities that people can partake in."

The study, which used samples that were gathered in 2021, is a continuation of a long-term monitoring program that began with the Department of Fisheries and Oceans in 1980. Sampling occurs roughly every 10 years.